Thread: Introduce a new Thread backend

This is a breaking change - see BREAKING-CHANGES.txt

BREAKING-CHANGES.txt

@@ -1,9 +1,37 @@
 JUCE breaking changes
 =====================
 
-develop
+Develop
 =======
 
+Change
+------
+The Thread::startThread (int) and Thread::setPriority (int) methods have been
+removed. A new Thread priority API has been introduced.
+
+Possible Issues
+---------------
+Code will fail to compile.
+
+Workaround
+----------
+Rather than using an integer thread priority you must instead use a value from
+the Thread::Priority enum. Thread::setPriority and Thread::getPriority should
+only be called from the target thread. To start a Thread with a realtime
+performance profile you must call startRealtimeThread.
+
+Rationale
+---------
+Operating systems are moving away from a specific thread priority and towards
+more granular control over which types of cores can be used and things like
+power throttling options. In particular, it is no longer possible to map a 0-10
+integer to a meaningful performance range on macOS ARM using the pthread
+interface. Using a more modern interface grants us access to more runtime
+options, but also changes how we can work with threads. The two most
+significant changes are that we cannot mix operations using the new and old
+interfaces, and that changing a priority using the new interface can only be
+done on the currently running thread.
+
 Change
 ------
 The constructor of WebBrowserComponent now requires passing in an instance of
@@ -40,7 +68,6 @@ browser backend is more intuitive then requiring the user to derive from a
 special class, especially if additional browser backends are added in the
 future.
 
-
 Change
 ------
 The function AudioIODeviceCallback::audioDeviceIOCallback() was removed.

examples/Audio/AudioPlaybackDemo.h

@@ -325,7 +325,7 @@ public:
         // audio setup
         formatManager.registerBasicFormats();
 
-        thread.startThread (3);
+        thread.startThread (Thread::Priority::normal);
 
        #ifndef JUCE_DEMO_RUNNER
         RuntimePermissions::request (RuntimePermissions::recordAudio,

examples/GUI/ImagesDemo.h

@@ -57,7 +57,7 @@ public:
     {
         setOpaque (true);
         imageList.setDirectory (File::getSpecialLocation (File::userPicturesDirectory), true, true);
-        directoryThread.startThread (1);
+        directoryThread.startThread (Thread::Priority::background);
 
         fileTree.setTitle ("Files");
         fileTree.addListener (this);

examples/GUI/VideoDemo.h

@@ -154,7 +154,7 @@ public:
         setOpaque (true);
 
         movieList.setDirectory (File::getSpecialLocation (File::userMoviesDirectory), true, true);
-        directoryThread.startThread (1);
+        directoryThread.startThread (Thread::Priority::background);
 
         fileTree.setTitle ("Files");
         fileTree.addListener (this);

examples/Plugins/ARAPluginDemo.h

@@ -63,7 +63,7 @@ public:
     SharedTimeSliceThread()
         : TimeSliceThread (String (JucePlugin_Name) + " ARA Sample Reading Thread")
     {
-        startThread (7);  // Above default priority so playback is fluent, but below realtime
+        startThread (Priority::high);  // Above default priority so playback is fluent, but below realtime
     }
 };
 

examples/Utilities/MultithreadingDemo.h

@@ -148,9 +148,7 @@ public:
         : BouncingBall (containerComp),
           Thread ("JUCE Demo Thread")
     {
-        // give the threads a random priority, so some will move more
+        startThread();
-        // smoothly than others..
-        startThread (Random::getSystemRandom().nextInt (3) + 3);
     }
 
     ~DemoThread() override

extras/Projucer/Source/Application/jucer_AutoUpdater.cpp

@@ -44,7 +44,7 @@ void LatestVersionCheckerAndUpdater::checkForNewVersion (bool background)
     if (! isThreadRunning())
     {
         backgroundCheck = background;
-        startThread (3);
+        startThread (Priority::low);
     }
 }
 
@@ -373,7 +373,7 @@ public:
         : ThreadWithProgressWindow ("Downloading New Version", true, true),
           asset (a), targetFolder (t), completionCallback (std::move (cb))
     {
-        launchThread (3);
+        launchThread (Priority::low);
     }
 
 private:

modules/juce_audio_devices/midi_io/juce_MidiDevices.cpp

@@ -87,7 +87,7 @@ void MidiOutput::clearAllPendingMessages()
 
 void MidiOutput::startBackgroundThread()
 {
-    startThread (9);
+    startThread (Priority::high);
 }
 
 void MidiOutput::stopBackgroundThread()

modules/juce_audio_devices/native/juce_android_Audio.cpp

@@ -253,7 +253,7 @@ public:
             if (inputDevice != nullptr)
                 env->CallVoidMethod (inputDevice, AudioRecord.startRecording);
 
-            startThread (8);
+            startThread (Priority::high);
         }
         else
         {

modules/juce_audio_devices/native/juce_linux_ALSA.cpp

@@ -618,7 +618,7 @@ public:
         if (outputDevice != nullptr && JUCE_ALSA_FAILED (snd_pcm_prepare (outputDevice->handle)))
             return;
 
-        startThread (9);
+        startThread (Priority::high);
 
         int count = 1000;
 

modules/juce_audio_devices/native/juce_win32_DirectSound.cpp

@@ -1196,7 +1196,7 @@ String DSoundAudioIODevice::openDevice (const BigInteger& inputChannels,
         for (int i = 0; i < inChans.size(); ++i)
             inChans.getUnchecked(i)->synchronisePosition();
 
-        startThread (9);
+        startThread (Priority::highest);
         sleep (10);
 
         notify();

modules/juce_audio_devices/native/juce_win32_WASAPI.cpp

@@ -1387,7 +1387,7 @@ public:
         shouldShutdown = false;
         deviceSampleRateChanged = false;
 
-        startThread (8);
+        startThread (Priority::high);
         Thread::sleep (5);
 
         if (inputDevice != nullptr && inputDevice->client != nullptr)

modules/juce_audio_formats/format/juce_BufferingAudioFormatReader.cpp

@@ -254,7 +254,7 @@ public:
     void runTest() override
     {
         TimeSliceThread timeSlice ("TestBackgroundThread");
-        timeSlice.startThread (5);
+        timeSlice.startThread (Thread::Priority::normal);
 
         beginTest ("Timeout");
         {

modules/juce_audio_plugin_client/utility/juce_LinuxMessageThread.h

@@ -25,8 +25,6 @@
 
 #if JUCE_LINUX || JUCE_BSD
 
-#include <thread>
-
 namespace juce
 {
 
@@ -34,15 +32,15 @@ namespace juce
 bool dispatchNextMessageOnSystemQueue (bool returnIfNoPendingMessages);
 
 /** @internal */
-class MessageThread
+class MessageThread : public Thread
 {
 public:
-    MessageThread()
+    MessageThread() : Thread ("JUCE Plugin Message Thread")
     {
         start();
     }
 
-    ~MessageThread()
+    ~MessageThread() override
     {
         MessageManager::getInstance()->stopDispatchLoop();
         stop();
@@ -50,51 +48,37 @@ public:
 
     void start()
     {
-        if (isRunning())
+        startThread (Priority::high);
-            stop();
 
-        shouldExit = false;
+        // Wait for setCurrentThreadAsMessageThread() and getInstance to be executed
-
+        // before leaving this method
-        thread = std::thread { [this]
+        threadInitialised.wait (10000);
-        {
-            Thread::setCurrentThreadPriority (7);
-            Thread::setCurrentThreadName ("JUCE Plugin Message Thread");
-
-            MessageManager::getInstance()->setCurrentThreadAsMessageThread();
-            XWindowSystem::getInstance();
-
-            threadInitialised.signal();
-
-            for (;;)
-            {
-                if (! dispatchNextMessageOnSystemQueue (true))
-                    Thread::sleep (1);
-
-                if (shouldExit)
-                    break;
-            }
-        } };
-
-        threadInitialised.wait();
     }
 
     void stop()
     {
-        if (! isRunning())
+        signalThreadShouldExit();
-            return;
+        stopThread (-1);
-
-        shouldExit = true;
-        thread.join();
     }
 
-    bool isRunning() const noexcept  { return thread.joinable(); }
+    bool isRunning() const noexcept  { return isThreadRunning(); }
+
+    void run() override
+    {
+        MessageManager::getInstance()->setCurrentThreadAsMessageThread();
+        XWindowSystem::getInstance();
+
+        threadInitialised.signal();
+
+        while (! threadShouldExit())
+        {
+            if (! dispatchNextMessageOnSystemQueue (true))
+                Thread::sleep (1);
+        }
+    }
 
 private:
     WaitableEvent threadInitialised;
-    std::thread thread;
-
-    std::atomic<bool> shouldExit { false };
-
     JUCE_DECLARE_NON_MOVEABLE (MessageThread)
     JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (MessageThread)
 };

modules/juce_audio_utils/gui/juce_AudioThumbnailCache.cpp

@@ -64,7 +64,7 @@ AudioThumbnailCache::AudioThumbnailCache (const int maxNumThumbs)
       maxNumThumbsToStore (maxNumThumbs)
 {
     jassert (maxNumThumbsToStore > 0);
-    thread.startThread (2);
+    thread.startThread (Thread::Priority::low);
 }
 
 AudioThumbnailCache::~AudioThumbnailCache()

modules/juce_core/juce_core.cpp

@@ -186,6 +186,7 @@
 #include "zip/juce_ZipFile.cpp"
 #include "files/juce_FileFilter.cpp"
 #include "files/juce_WildcardFileFilter.cpp"
+#include "native/juce_native_ThreadPriorities.h"
 
 //==============================================================================
 #if ! JUCE_WINDOWS

modules/juce_core/native/juce_BasicNativeHeaders.h

@@ -203,6 +203,7 @@
  #include <sys/ptrace.h>
  #include <sys/socket.h>
  #include <sys/stat.h>
+ #include <sys/syscall.h>
  #include <sys/sysinfo.h>
  #include <sys/time.h>
  #include <sys/types.h>

modules/juce_core/native/juce_android_Threads.cpp

@@ -344,36 +344,79 @@ LocalRef<jobject> getMainActivity() noexcept
 }
 
 //==============================================================================
-// sets the process to 0=low priority, 1=normal, 2=high, 3=realtime
+#if JUCE_ANDROID && JUCE_MODULE_AVAILABLE_juce_audio_devices && (JUCE_USE_ANDROID_OPENSLES || JUCE_USE_ANDROID_OBOE)
-JUCE_API void JUCE_CALLTYPE Process::setPriority (ProcessPriority prior)
+ #define JUCE_ANDROID_REALTIME_THREAD_AVAILABLE 1
+#endif
+
+#if JUCE_ANDROID_REALTIME_THREAD_AVAILABLE
+pthread_t juce_createRealtimeAudioThread (void* (*entry) (void*), void* userPtr);
+#endif
+
+extern JavaVM* androidJNIJavaVM;
+
+bool Thread::createNativeThread (Priority)
 {
-    // TODO
+    if (isRealtime())
+    {
+       #if JUCE_ANDROID_REALTIME_THREAD_AVAILABLE
+        threadHandle = (void*) juce_createRealtimeAudioThread (threadEntryProc, this);
+        threadId = (ThreadID) threadHandle.get();
+        return threadId != nullptr;
+       #else
+        jassertfalse;
+       #endif
+    }
 
-    struct sched_param param;
+    PosixThreadAttribute attr { threadStackSize };
-    int policy, maxp, minp;
+    threadId = threadHandle = makeThreadHandle (attr, this, [] (void* userData) -> void*
+    {
+        auto* myself = static_cast<Thread*> (userData);
 
-    const int p = (int) prior;
+        juce_threadEntryPoint (myself);
 
-    if (p <= 1)
+        if (androidJNIJavaVM != nullptr)
-        policy = SCHED_OTHER;
+        {
-    else
+            void* env = nullptr;
-        policy = SCHED_RR;
+            androidJNIJavaVM->GetEnv (&env, JNI_VERSION_1_2);
 
-    minp = sched_get_priority_min (policy);
+            // only detach if we have actually been attached
-    maxp = sched_get_priority_max (policy);
+            if (env != nullptr)
+                androidJNIJavaVM->DetachCurrentThread();
+        }
 
-    if (p < 2)
+        return nullptr;
-        param.sched_priority = 0;
+    });
-    else if (p == 2 )
-        // Set to middle of lower realtime priority range
-        param.sched_priority = minp + (maxp - minp) / 4;
-    else
-        // Set to middle of higher realtime priority range
-        param.sched_priority = minp + (3 * (maxp - minp) / 4);
 
-    pthread_setschedparam (pthread_self(), policy, &param);
+    return threadId != nullptr;
 }
 
+void Thread::killThread()
+{
+    if (threadHandle != nullptr)
+        jassertfalse; // pthread_cancel not available!
+}
+
+Thread::Priority Thread::getPriority() const
+{
+    jassert (Thread::getCurrentThreadId() == getThreadId());
+
+    const auto native = getpriority (PRIO_PROCESS, (id_t) gettid());
+    return ThreadPriorities::getJucePriority (native);
+}
+
+bool Thread::setPriority (Priority)
+{
+    jassert (Thread::getCurrentThreadId() == getThreadId());
+
+    if (isRealtime())
+        return false;
+
+    return setpriority (PRIO_PROCESS, (id_t) gettid(), ThreadPriorities::getNativePriority (priority)) == 0;
+}
+
+//==============================================================================
+JUCE_API void JUCE_CALLTYPE Process::setPriority (ProcessPriority) {}
+
 JUCE_API bool JUCE_CALLTYPE juce_isRunningUnderDebugger() noexcept
 {
     StringArray lines;

modules/juce_core/native/juce_linux_Threads.cpp

@@ -28,27 +28,49 @@ namespace juce
     live in juce_posix_SharedCode.h!
 */
 
-//==============================================================================
+bool Thread::createNativeThread (Priority)
-JUCE_API void JUCE_CALLTYPE Process::setPriority (const ProcessPriority prior)
 {
-    auto policy = (prior <= NormalPriority) ? SCHED_OTHER : SCHED_RR;
+    PosixThreadAttribute attr { threadStackSize };
-    auto minp = sched_get_priority_min (policy);
+    PosixSchedulerPriority::getNativeSchedulerAndPriority (realtimeOptions, {}).apply (attr);
-    auto maxp = sched_get_priority_max (policy);
 
-    struct sched_param param;
+    threadId = threadHandle = makeThreadHandle (attr, this, [] (void* userData) -> void*
-
-    switch (prior)
     {
-        case LowPriority:
+        auto* myself = static_cast<Thread*> (userData);
-        case NormalPriority:    param.sched_priority = 0; break;
-        case HighPriority:      param.sched_priority = minp + (maxp - minp) / 4; break;
-        case RealtimePriority:  param.sched_priority = minp + (3 * (maxp - minp) / 4); break;
-        default:                jassertfalse; break;
-    }
 
-    pthread_setschedparam (pthread_self(), policy, &param);
+        juce_threadEntryPoint (myself);
+
+        return nullptr;
+    });
+
+    return threadId != nullptr;
 }
 
+void Thread::killThread()
+{
+    if (threadHandle != nullptr)
+        pthread_cancel ((pthread_t) threadHandle.load());
+}
+
+// Until we implement Nice awareness, these don't do anything on Linux.
+Thread::Priority Thread::getPriority() const
+{
+    jassert (Thread::getCurrentThreadId() == getThreadId());
+
+    return priority;
+}
+
+bool Thread::setPriority (Priority newPriority)
+{
+    jassert (Thread::getCurrentThreadId() == getThreadId());
+
+    // Return true to make it compatible with other platforms.
+    priority = newPriority;
+    return true;
+}
+
+//==============================================================================
+JUCE_API void JUCE_CALLTYPE Process::setPriority (ProcessPriority) {}
+
 static bool swapUserAndEffectiveUser()
 {
     auto result1 = setreuid (geteuid(), getuid());

modules/juce_core/native/juce_mac_Threads.mm

@@ -29,9 +29,139 @@ namespace juce
 */
 
 #if JUCE_IOS
-bool isIOSAppActive = true;
+ bool isIOSAppActive = true;
 #endif
 
+API_AVAILABLE (macos (10.10))
+static auto getNativeQOS (Thread::Priority priority)
+{
+    switch (priority)
+    {
+        case Thread::Priority::highest:    return QOS_CLASS_USER_INTERACTIVE;
+        case Thread::Priority::high:       return QOS_CLASS_USER_INITIATED;
+        case Thread::Priority::low:        return QOS_CLASS_UTILITY;
+        case Thread::Priority::background: return QOS_CLASS_BACKGROUND;
+        case Thread::Priority::normal:     break;
+    }
+
+    return QOS_CLASS_DEFAULT;
+}
+
+API_AVAILABLE (macos (10.10))
+static auto getJucePriority (qos_class_t qos)
+{
+    switch (qos)
+    {
+        case QOS_CLASS_USER_INTERACTIVE:    return Thread::Priority::highest;
+        case QOS_CLASS_USER_INITIATED:      return Thread::Priority::high;
+        case QOS_CLASS_UTILITY:             return Thread::Priority::low;
+        case QOS_CLASS_BACKGROUND:          return Thread::Priority::background;
+
+        case QOS_CLASS_UNSPECIFIED:
+        case QOS_CLASS_DEFAULT:             break;
+    }
+
+    return Thread::Priority::normal;
+}
+
+bool Thread::createNativeThread (Priority priority)
+{
+    PosixThreadAttribute attr { threadStackSize };
+
+    if (@available (macos 10.10, *))
+        pthread_attr_set_qos_class_np (attr.get(), getNativeQOS (priority), 0);
+    else
+        PosixSchedulerPriority::getNativeSchedulerAndPriority (realtimeOptions, priority).apply (attr);
+
+    threadId = threadHandle = makeThreadHandle (attr, this, [] (void* userData) -> void*
+    {
+        auto* myself = static_cast<Thread*> (userData);
+
+        JUCE_AUTORELEASEPOOL
+        {
+            juce_threadEntryPoint (myself);
+        }
+
+        return nullptr;
+    });
+
+    return threadId != nullptr;
+}
+
+void Thread::killThread()
+{
+    if (threadHandle != nullptr)
+        pthread_cancel ((pthread_t) threadHandle.load());
+}
+
+Thread::Priority Thread::getPriority() const
+{
+    jassert (Thread::getCurrentThreadId() == getThreadId());
+
+    if (! isRealtime())
+    {
+        if (@available (macOS 10.10, *))
+            return getJucePriority (qos_class_self());
+
+        // fallback for older versions of macOS
+        const auto min = jmax (0, sched_get_priority_min (SCHED_OTHER));
+        const auto max = jmax (0, sched_get_priority_max (SCHED_OTHER));
+
+        if (min != 0 && max != 0)
+        {
+            const auto native = PosixSchedulerPriority::findCurrentSchedulerAndPriority().getPriority();
+            const auto mapped = jmap (native, min, max, 0, 4);
+            return ThreadPriorities::getJucePriority (mapped);
+        }
+    }
+
+    return {};
+}
+
+bool Thread::setPriority (Priority priority)
+{
+    jassert (Thread::getCurrentThreadId() == getThreadId());
+
+    if (isRealtime())
+    {
+        // macOS/iOS needs to know how much time you need!
+        jassert (realtimeOptions->workDurationMs > 0);
+
+        mach_timebase_info_data_t timebase;
+        mach_timebase_info (&timebase);
+
+        const auto periodMs = realtimeOptions->workDurationMs;
+        const auto ticksPerMs = ((double) timebase.denom * 1000000.0) / (double) timebase.numer;
+        const auto periodTicks = (uint32_t) jmin ((double) std::numeric_limits<uint32_t>::max(), periodMs * ticksPerMs);
+
+        thread_time_constraint_policy_data_t policy;
+        policy.period = periodTicks;
+        policy.computation = jmin ((uint32_t) 50000, policy.period);
+        policy.constraint = policy.period;
+        policy.preemptible = true;
+
+        return thread_policy_set (pthread_mach_thread_np (pthread_self()),
+                                  THREAD_TIME_CONSTRAINT_POLICY,
+                                  (thread_policy_t) &policy,
+                                  THREAD_TIME_CONSTRAINT_POLICY_COUNT) == KERN_SUCCESS;
+    }
+
+    if (@available (macOS 10.10, *))
+        return pthread_set_qos_class_self_np (getNativeQOS (priority), 0) == 0;
+
+   #if JUCE_ARM
+    // M1 platforms should never reach this code!!!!!!
+    jassertfalse;
+   #endif
+
+    // Just in case older versions of macOS support SCHED_OTHER priorities.
+    const auto psp = PosixSchedulerPriority::getNativeSchedulerAndPriority ({}, priority);
+
+    struct sched_param param;
+    param.sched_priority = psp.getPriority();
+    return pthread_setschedparam (pthread_self(), psp.getScheduler(), &param) == 0;
+}
+
 //==============================================================================
 JUCE_API bool JUCE_CALLTYPE Process::isForegroundProcess()
 {

modules/juce_core/native/juce_native_ThreadPriorities.h

@@ -0,0 +1,109 @@
+/*
+  ==============================================================================
+
+   This file is part of the JUCE library.
+   Copyright (c) 2022 - Raw Material Software Limited
+
+   JUCE is an open source library subject to commercial or open-source
+   licensing.
+
+   The code included in this file is provided under the terms of the ISC license
+   http://www.isc.org/downloads/software-support-policy/isc-license. Permission
+   To use, copy, modify, and/or distribute this software for any purpose with or
+   without fee is hereby granted provided that the above copyright notice and
+   this permission notice appear in all copies.
+
+   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
+   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
+   DISCLAIMED.
+
+  ==============================================================================
+*/
+
+namespace juce
+{
+
+struct ThreadPriorities
+{
+    struct Entry
+    {
+        Thread::Priority priority;
+        int native;
+    };
+
+   #if JUCE_ANDROID
+    enum AndroidThreadPriority
+    {
+        THREAD_PRIORITY_AUDIO          = -16,
+        THREAD_PRIORITY_FOREGROUND     = -2,
+        THREAD_PRIORITY_MORE_FAVORABLE = -1,
+        THREAD_PRIORITY_DEFAULT        = 0,
+        THREAD_PRIORITY_LESS_FAVORABLE = 1,
+        THREAD_PRIORITY_BACKGROUND     = 10,
+        THREAD_PRIORITY_LOWEST         = 19
+    };
+   #endif
+
+    inline static constexpr Entry table[]
+    {
+       #if JUCE_ANDROID
+        { Thread::Priority::highest,    AndroidThreadPriority::THREAD_PRIORITY_AUDIO },
+        { Thread::Priority::high,       AndroidThreadPriority::THREAD_PRIORITY_FOREGROUND },
+        { Thread::Priority::normal,     AndroidThreadPriority::THREAD_PRIORITY_DEFAULT },
+        { Thread::Priority::low,        AndroidThreadPriority::THREAD_PRIORITY_BACKGROUND - 5 },
+        { Thread::Priority::background, AndroidThreadPriority::THREAD_PRIORITY_BACKGROUND },
+       #endif
+
+       #if JUCE_LINUX || JUCE_BSD
+        { Thread::Priority::highest,    0 },
+        { Thread::Priority::high,       0 },
+        { Thread::Priority::normal,     0 },
+        { Thread::Priority::low,        0 },
+        { Thread::Priority::background, 0 },
+       #endif
+
+       #if JUCE_MAC | JUCE_IOS
+        { Thread::Priority::highest,    4 },
+        { Thread::Priority::high,       3 },
+        { Thread::Priority::normal,     2 },
+        { Thread::Priority::low,        1 },
+        { Thread::Priority::background, 0 },
+       #endif
+
+       #if JUCE_WINDOWS
+        { Thread::Priority::highest,    THREAD_PRIORITY_TIME_CRITICAL },
+        { Thread::Priority::high,       THREAD_PRIORITY_HIGHEST },
+        { Thread::Priority::normal,     THREAD_PRIORITY_NORMAL },
+        { Thread::Priority::low,        THREAD_PRIORITY_LOWEST },
+        { Thread::Priority::background, THREAD_PRIORITY_IDLE },
+       #endif
+    };
+
+    static_assert (std::size (table) == 5,
+                   "The platform may be unsupported or there may be a priority entry missing.");
+
+    static Thread::Priority getJucePriority (const int value)
+    {
+        const auto iter = std::min_element (std::begin (table),
+                                            std::end   (table),
+                                            [value] (const auto& a, const auto& b)
+                                            {
+                                                return std::abs (a.native - value) < std::abs (b.native - value);
+                                            });
+
+        jassert (iter != std::end (table));
+        return iter != std::end (table) ? iter->priority : Thread::Priority{};
+    }
+
+    static int getNativePriority (const Thread::Priority value)
+    {
+        const auto iter = std::find_if (std::begin (table),
+                                        std::end   (table),
+                                        [value] (const auto& entry) { return entry.priority == value; });
+
+        jassert (iter != std::end (table));
+        return iter != std::end (table) ? iter->native : 0;
+    }
+};
+
+} // namespace juce

modules/juce_core/native/juce_posix_SharedCode.h

@@ -851,98 +851,131 @@ void InterProcessLock::exit()
         pimpl.reset();
 }
 
-//==============================================================================
+class PosixThreadAttribute
-#if JUCE_ANDROID
-extern JavaVM* androidJNIJavaVM;
-#endif
-
-static void* threadEntryProc (void* userData)
 {
-    auto* myself = static_cast<Thread*> (userData);
+public:
-
+    explicit PosixThreadAttribute (size_t stackSize)
-    JUCE_AUTORELEASEPOOL
     {
-        juce_threadEntryPoint (myself);
+        if (valid)
+            pthread_attr_setstacksize (&attr, stackSize);
     }
 
-   #if JUCE_ANDROID
+    ~PosixThreadAttribute()
-    if (androidJNIJavaVM != nullptr)
     {
-        void* env = nullptr;
+        if (valid)
-        androidJNIJavaVM->GetEnv(&env, JNI_VERSION_1_2);
+            pthread_attr_destroy (&attr);
-
-        // only detach if we have actually been attached
-        if (env != nullptr)
-            androidJNIJavaVM->DetachCurrentThread();
     }
-   #endif
 
-    return nullptr;
+    auto* get() { return valid ? &attr : nullptr; }
-}
 
-#if JUCE_ANDROID && JUCE_MODULE_AVAILABLE_juce_audio_devices && (JUCE_USE_ANDROID_OPENSLES || JUCE_USE_ANDROID_OBOE)
+private:
- #define JUCE_ANDROID_REALTIME_THREAD_AVAILABLE 1
-#endif
-
-#if JUCE_ANDROID_REALTIME_THREAD_AVAILABLE
-extern pthread_t juce_createRealtimeAudioThread (void* (*entry) (void*), void* userPtr);
-#endif
-
-void Thread::launchThread()
-{
-   #if JUCE_ANDROID
-    if (isAndroidRealtimeThread)
-    {
-       #if JUCE_ANDROID_REALTIME_THREAD_AVAILABLE
-        threadHandle = (void*) juce_createRealtimeAudioThread (threadEntryProc, this);
-        threadId = (ThreadID) threadHandle.get();
-
-        return;
-       #else
-        jassertfalse;
-       #endif
-    }
-   #endif
-
-    threadHandle = {};
-    pthread_t handle = {};
     pthread_attr_t attr;
-    pthread_attr_t* attrPtr = nullptr;
+    bool valid { pthread_attr_init (&attr) == 0 };
+};
 
-    if (pthread_attr_init (&attr) == 0)
+class PosixSchedulerPriority
+{
+public:
+    static PosixSchedulerPriority findCurrentSchedulerAndPriority()
     {
-        attrPtr = &attr;
+        int scheduler{};
-        pthread_attr_setstacksize (attrPtr, threadStackSize);
+        sched_param param{};
+        pthread_getschedparam (pthread_self(), &scheduler, &param);
+        return { scheduler, param.sched_priority };
     }
 
-
+    static PosixSchedulerPriority getNativeSchedulerAndPriority (const Optional<Thread::RealtimeOptions>& rt,
-    if (pthread_create (&handle, attrPtr, threadEntryProc, this) == 0)
+                                                                 [[maybe_unused]] Thread::Priority prio)
     {
-        pthread_detach (handle);
+        const auto isRealtime = rt.hasValue();
-        threadHandle = (void*) handle;
+
-        threadId = (ThreadID) threadHandle.get();
+        const auto priority = [&]
+        {
+            if (isRealtime)
+            {
+                const auto min = jmax (0, sched_get_priority_min (SCHED_RR));
+                const auto max = jmax (1, sched_get_priority_max (SCHED_RR));
+
+                return jmap (rt->priority, 0, 10, min, max);
+            }
+
+            // We only use this helper if we're on an old macos/ios platform that might
+            // still respect legacy pthread priorities for SCHED_OTHER.
+            #if JUCE_MAC || JUCE_IOS
+             const auto min = jmax (0, sched_get_priority_min (SCHED_OTHER));
+             const auto max = jmax (0, sched_get_priority_max (SCHED_OTHER));
+
+             const auto p = [prio]
+             {
+                 switch (prio)
+                 {
+                     case Thread::Priority::highest:    return 4;
+                     case Thread::Priority::high:       return 3;
+                     case Thread::Priority::normal:     return 2;
+                     case Thread::Priority::low:        return 1;
+                     case Thread::Priority::background: return 0;
+                 }
+
+                 return 3;
+             }();
+
+             if (min != 0 && max != 0)
+                 return jmap (p, 0, 4, min, max);
+            #endif
+
+            return 0;
+        }();
+
+        #if JUCE_MAC || JUCE_IOS
+         const auto scheduler = SCHED_OTHER;
+        #elif JUCE_LINUX || JUCE_BSD
+         const auto backgroundSched = prio == Thread::Priority::background ? SCHED_IDLE
+                                                                           : SCHED_OTHER;
+         const auto scheduler = isRealtime ? SCHED_RR : backgroundSched;
+        #else
+         const auto scheduler = 0;
+        #endif
+
+         return { scheduler, priority };
     }
 
-    if (attrPtr != nullptr)
+    void apply ([[maybe_unused]] PosixThreadAttribute& attr) const
-        pthread_attr_destroy (attrPtr);
+    {
+        #if JUCE_LINUX || JUCE_BSD
+         const struct sched_param param { getPriority() };
+
+         pthread_attr_setinheritsched (attr.get(), PTHREAD_EXPLICIT_SCHED);
+         pthread_attr_setschedpolicy (attr.get(), getScheduler());
+         pthread_attr_setschedparam (attr.get(), &param);
+        #endif
+    }
+
+    constexpr int getScheduler() const { return scheduler; }
+    constexpr int  getPriority() const { return priority; }
+
+private:
+    constexpr PosixSchedulerPriority (int schedulerIn, int priorityIn)
+        : scheduler (schedulerIn), priority (priorityIn) {}
+
+    int scheduler;
+    int priority;
+};
+
+static void* makeThreadHandle (PosixThreadAttribute& attr, Thread* userData, void* (*threadEntryProc) (void*))
+{
+    pthread_t handle = {};
+
+    if (pthread_create (&handle, attr.get(), threadEntryProc, userData) != 0)
+        return nullptr;
+
+    pthread_detach (handle);
+    return (void*) handle;
 }
 
 void Thread::closeThreadHandle()
 {
     threadId = {};
-    threadHandle = {};
+    threadHandle = nullptr;
-}
-
-void Thread::killThread()
-{
-    if (threadHandle.get() != nullptr)
-    {
-       #if JUCE_ANDROID
-        jassertfalse; // pthread_cancel not available!
-       #else
-        pthread_cancel ((pthread_t) threadHandle.get());
-       #endif
-    }
 }
 
 void JUCE_CALLTYPE Thread::setCurrentThreadName (const String& name)
@@ -963,41 +996,6 @@ void JUCE_CALLTYPE Thread::setCurrentThreadName (const String& name)
    #endif
 }
 
-bool Thread::setThreadPriority (void* handle, int priority)
-{
-    constexpr auto maxInputPriority = 10;
-
-   #if JUCE_LINUX || JUCE_BSD
-    constexpr auto lowestRrPriority = 8;
-   #else
-    constexpr auto lowestRrPriority = 0;
-   #endif
-
-    struct sched_param param;
-    int policy;
-
-    if (handle == nullptr)
-        handle = (void*) pthread_self();
-
-    if (pthread_getschedparam ((pthread_t) handle, &policy, &param) != 0)
-        return false;
-
-    policy = priority < lowestRrPriority ? SCHED_OTHER : SCHED_RR;
-
-    const auto minPriority = sched_get_priority_min (policy);
-    const auto maxPriority = sched_get_priority_max (policy);
-
-    param.sched_priority = [&]
-    {
-        if (policy == SCHED_OTHER)
-            return 0;
-
-        return jmap (priority, lowestRrPriority, maxInputPriority, minPriority, maxPriority);
-    }();
-
-    return pthread_setschedparam ((pthread_t) handle, policy, &param) == 0;
-}
-
 Thread::ThreadID JUCE_CALLTYPE Thread::getCurrentThreadId()
 {
     return (ThreadID) pthread_self();
@@ -1262,145 +1260,4 @@ bool ChildProcess::start (const StringArray& args, int streamFlags)
 
 #endif
 
-//==============================================================================
-struct HighResolutionTimer::Pimpl
-{
-    explicit Pimpl (HighResolutionTimer& t)
-        : owner (t)
-    {}
-
-    ~Pimpl()
-    {
-        jassert (periodMs == 0);
-        stop();
-    }
-
-    void start (int newPeriod)
-    {
-        if (periodMs == newPeriod)
-            return;
-
-        if (thread.get_id() == std::this_thread::get_id())
-        {
-            periodMs = newPeriod;
-            return;
-        }
-
-        stop();
-
-        periodMs = newPeriod;
-
-        thread = std::thread ([this, newPeriod]
-        {
-            setThisThreadToRealtime ((uint64) newPeriod);
-
-            auto lastPeriod = periodMs.load();
-            Clock clock (lastPeriod);
-
-            std::unique_lock<std::mutex> unique_lock (timerMutex);
-
-            while (periodMs != 0)
-            {
-                clock.next();
-                while (periodMs != 0 && clock.wait (stopCond, unique_lock));
-
-                if (periodMs == 0)
-                    break;
-
-                owner.hiResTimerCallback();
-
-                auto nextPeriod = periodMs.load();
-
-                if (lastPeriod != nextPeriod)
-                {
-                    lastPeriod = nextPeriod;
-                    clock = Clock (lastPeriod);
-                }
-            }
-
-            periodMs = 0;
-        });
-    }
-
-    void stop()
-    {
-        periodMs = 0;
-
-        const auto thread_id = thread.get_id();
-
-        if (thread_id == std::thread::id() || thread_id == std::this_thread::get_id())
-            return;
-
-        {
-            std::unique_lock<std::mutex> unique_lock (timerMutex);
-            stopCond.notify_one();
-        }
-
-        thread.join();
-    }
-
-    HighResolutionTimer& owner;
-    std::atomic<int> periodMs { 0 };
-
-private:
-    std::thread thread;
-    std::condition_variable stopCond;
-    std::mutex timerMutex;
-
-    class Clock
-    {
-    public:
-        explicit Clock (std::chrono::steady_clock::rep millis) noexcept
-            : time (std::chrono::steady_clock::now()),
-              delta (std::chrono::milliseconds (millis))
-        {}
-
-        bool wait (std::condition_variable& cond, std::unique_lock<std::mutex>& lock) noexcept
-        {
-            return cond.wait_until (lock, time) != std::cv_status::timeout;
-        }
-
-        void next() noexcept
-        {
-            time += delta;
-        }
-
-    private:
-        std::chrono::time_point<std::chrono::steady_clock> time;
-        std::chrono::steady_clock::duration delta;
-    };
-
-    static bool setThisThreadToRealtime (uint64 periodMs)
-    {
-        const auto thread = pthread_self();
-
-       #if JUCE_MAC || JUCE_IOS
-        mach_timebase_info_data_t timebase;
-        mach_timebase_info (&timebase);
-
-        const auto ticksPerMs = ((double) timebase.denom * 1000000.0) / (double) timebase.numer;
-        const auto periodTicks = (uint32_t) jmin ((double) std::numeric_limits<uint32_t>::max(), periodMs * ticksPerMs);
-
-        thread_time_constraint_policy_data_t policy;
-        policy.period      = periodTicks;
-        policy.computation = jmin ((uint32_t) 50000, policy.period);
-        policy.constraint  = policy.period;
-        policy.preemptible = true;
-
-        return thread_policy_set (pthread_mach_thread_np (thread),
-                                  THREAD_TIME_CONSTRAINT_POLICY,
-                                  (thread_policy_t) &policy,
-                                  THREAD_TIME_CONSTRAINT_POLICY_COUNT) == KERN_SUCCESS;
-
-       #else
-        ignoreUnused (periodMs);
-        struct sched_param param;
-        param.sched_priority = sched_get_priority_max (SCHED_RR);
-        return pthread_setschedparam (thread, SCHED_RR, &param) == 0;
-       #endif
-    }
-
-    JUCE_DECLARE_NON_COPYABLE (Pimpl)
-};
-
 } // namespace juce

modules/juce_core/native/juce_win32_Threads.cpp

@@ -51,7 +51,6 @@ void CriticalSection::enter() const noexcept        { EnterCriticalSection ((CRI
 bool CriticalSection::tryEnter() const noexcept     { return TryEnterCriticalSection ((CRITICAL_SECTION*) &lock) != FALSE; }
 void CriticalSection::exit() const noexcept         { LeaveCriticalSection ((CRITICAL_SECTION*) &lock); }
 
-
 //==============================================================================
 static unsigned int STDMETHODCALLTYPE threadEntryProc (void* userData)
 {
@@ -65,31 +64,72 @@ static unsigned int STDMETHODCALLTYPE threadEntryProc (void* userData)
     return 0;
 }
 
-void Thread::launchThread()
+static bool setPriorityInternal (bool isRealtime, HANDLE handle, Thread::Priority priority)
+{
+    auto nativeThreadFlag = isRealtime ? THREAD_PRIORITY_TIME_CRITICAL
+                                       : ThreadPriorities::getNativePriority (priority);
+
+    if (isRealtime) // This should probably be a fail state too?
+        Process::setPriority (Process::ProcessPriority::RealtimePriority);
+
+    return SetThreadPriority (handle, nativeThreadFlag);
+}
+
+bool Thread::createNativeThread (Priority priority)
 {
     unsigned int newThreadId;
     threadHandle = (void*) _beginthreadex (nullptr, (unsigned int) threadStackSize,
-                                           &threadEntryProc, this, 0, &newThreadId);
+                                           &threadEntryProc, this, CREATE_SUSPENDED,
-    threadId = (ThreadID) (pointer_sized_int) newThreadId;
+                                           &newThreadId);
+
+    if (threadHandle != nullptr)
+    {
+        threadId = (ThreadID) (pointer_sized_int) newThreadId;
+
+        if (setPriorityInternal (isRealtime(), threadHandle, priority))
+        {
+            ResumeThread (threadHandle);
+            return true;
+        }
+
+        killThread();
+        closeThreadHandle();
+    }
+
+    return false;
+}
+
+Thread::Priority Thread::getPriority() const
+{
+    jassert (Thread::getCurrentThreadId() == getThreadId());
+
+    const auto native = GetThreadPriority (threadHandle);
+    return ThreadPriorities::getJucePriority (native);
+}
+
+bool Thread::setPriority (Priority priority)
+{
+    jassert (Thread::getCurrentThreadId() == getThreadId());
+    return setPriorityInternal (isRealtime(), this, priority);
 }
 
 void Thread::closeThreadHandle()
 {
-    CloseHandle ((HANDLE) threadHandle.get());
+    CloseHandle (threadHandle);
     threadId = nullptr;
     threadHandle = nullptr;
 }
 
 void Thread::killThread()
 {
-    if (threadHandle.get() != nullptr)
+    if (threadHandle != nullptr)
     {
        #if JUCE_DEBUG
         OutputDebugStringA ("** Warning - Forced thread termination **\n");
        #endif
 
         JUCE_BEGIN_IGNORE_WARNINGS_MSVC (6258)
-        TerminateThread (threadHandle.get(), 0);
+        TerminateThread (threadHandle, 0);
         JUCE_END_IGNORE_WARNINGS_MSVC
     }
 }
@@ -129,23 +169,6 @@ Thread::ThreadID JUCE_CALLTYPE Thread::getCurrentThreadId()
     return (ThreadID) (pointer_sized_int) GetCurrentThreadId();
 }
 
-bool Thread::setThreadPriority (void* handle, int priority)
-{
-    int pri = THREAD_PRIORITY_TIME_CRITICAL;
-
-    if (priority < 1)       pri = THREAD_PRIORITY_IDLE;
-    else if (priority < 2)  pri = THREAD_PRIORITY_LOWEST;
-    else if (priority < 5)  pri = THREAD_PRIORITY_BELOW_NORMAL;
-    else if (priority < 7)  pri = THREAD_PRIORITY_NORMAL;
-    else if (priority < 9)  pri = THREAD_PRIORITY_ABOVE_NORMAL;
-    else if (priority < 10) pri = THREAD_PRIORITY_HIGHEST;
-
-    if (handle == nullptr)
-        handle = GetCurrentThread();
-
-    return SetThreadPriority (handle, pri) != FALSE;
-}
-
 void JUCE_CALLTYPE Thread::setCurrentThreadAffinityMask (const uint32 affinityMask)
 {
     SetThreadAffinityMask (GetCurrentThread(), affinityMask);
@@ -217,11 +240,11 @@ void juce_repeatLastProcessPriority()
     }
 }
 
-void JUCE_CALLTYPE Process::setPriority (ProcessPriority prior)
+void JUCE_CALLTYPE Process::setPriority (ProcessPriority newPriority)
 {
-    if (lastProcessPriority != (int) prior)
+    if (lastProcessPriority != (int) newPriority)
     {
-        lastProcessPriority = (int) prior;
+        lastProcessPriority = (int) newPriority;
         juce_repeatLastProcessPriority();
     }
 }
@@ -527,56 +550,4 @@ bool ChildProcess::start (const StringArray& args, int streamFlags)
     return start (escaped.trim(), streamFlags);
 }
 
-//==============================================================================
-struct HighResolutionTimer::Pimpl
-{
-    Pimpl (HighResolutionTimer& t) noexcept  : owner (t)
-    {
-    }
-
-    ~Pimpl()
-    {
-        jassert (periodMs == 0);
-    }
-
-    void start (int newPeriod)
-    {
-        if (newPeriod != periodMs)
-        {
-            stop();
-            periodMs = newPeriod;
-
-            TIMECAPS tc;
-            if (timeGetDevCaps (&tc, sizeof (tc)) == TIMERR_NOERROR)
-            {
-                const int actualPeriod = jlimit ((int) tc.wPeriodMin, (int) tc.wPeriodMax, newPeriod);
-
-                timerID = timeSetEvent ((UINT) actualPeriod, tc.wPeriodMin, callbackFunction, (DWORD_PTR) this,
-                                        TIME_PERIODIC | TIME_CALLBACK_FUNCTION | 0x100 /*TIME_KILL_SYNCHRONOUS*/);
-            }
-        }
-    }
-
-    void stop()
-    {
-        periodMs = 0;
-        timeKillEvent (timerID);
-    }
-
-    HighResolutionTimer& owner;
-    int periodMs = 0;
-
-private:
-    unsigned int timerID;
-
-    static void STDMETHODCALLTYPE callbackFunction (UINT, UINT, DWORD_PTR userInfo, DWORD_PTR, DWORD_PTR)
-    {
-        if (Pimpl* const timer = reinterpret_cast<Pimpl*> (userInfo))
-            if (timer->periodMs != 0)
-                timer->owner.hiResTimerCallback();
-    }
-
-    JUCE_DECLARE_NON_COPYABLE (Pimpl)
-};
-
 } // namespace juce

modules/juce_core/system/juce_SystemStats.h

@@ -243,7 +243,6 @@ public:
     */
     static bool isRunningInAppExtensionSandbox() noexcept;
 
-
     //==============================================================================
    #ifndef DOXYGEN
     [[deprecated ("This method was spelt wrong! Please change your code to use getCpuSpeedInMegahertz instead.")]]

modules/juce_core/threads/juce_HighResolutionTimer.cpp

@@ -23,13 +23,96 @@
 namespace juce
 {
 
-HighResolutionTimer::HighResolutionTimer() : pimpl (new Pimpl (*this)) {}
+class HighResolutionTimer::Pimpl : private Thread
-HighResolutionTimer::~HighResolutionTimer()                   { stopTimer(); }
+{
+    using steady_clock = std::chrono::steady_clock;
+    using milliseconds = std::chrono::milliseconds;
 
-void HighResolutionTimer::startTimer (int periodMs)           { pimpl->start (jmax (1, periodMs)); }
+public:
-void HighResolutionTimer::stopTimer()                         { pimpl->stop(); }
+    explicit Pimpl (HighResolutionTimer& ownerRef)
+        : Thread ("HighResolutionTimerThread"),
+          owner (ownerRef)
+    {
+    }
 
-bool HighResolutionTimer::isTimerRunning() const noexcept     { return pimpl->periodMs != 0; }
+    using Thread::isThreadRunning;
-int HighResolutionTimer::getTimerInterval() const noexcept    { return pimpl->periodMs; }
+
+    void start (int periodMs)
+    {
+        {
+            const std::scoped_lock lk { mutex };
+            periodMillis = periodMs;
+            nextTickTime = steady_clock::now() + milliseconds (periodMillis);
+        }
+
+        if (! isThreadRunning())
+            startThread (Thread::Priority::high);
+    }
+
+    void stop()
+    {
+        {
+            const std::scoped_lock lk { mutex };
+            periodMillis = 0;
+        }
+
+        waitEvent.notify_one();
+
+        if (Thread::getCurrentThreadId() != getThreadId())
+            stopThread (-1);
+    }
+
+    int getPeriod() const
+    {
+        return periodMillis;
+    }
+
+private:
+    void run() override
+    {
+        for (;;)
+        {
+            {
+                std::unique_lock lk { mutex };
+
+                if (waitEvent.wait_until (lk, nextTickTime, [this] { return periodMillis == 0; }))
+                    break;
+
+                nextTickTime = steady_clock::now() + milliseconds (periodMillis);
+            }
+
+            owner.hiResTimerCallback();
+        }
+    }
+
+    HighResolutionTimer& owner;
+    std::atomic<int> periodMillis { 0 };
+    steady_clock::time_point nextTickTime;
+    std::mutex mutex;
+    std::condition_variable waitEvent;
+};
+
+HighResolutionTimer::HighResolutionTimer()
+    : pimpl (new Pimpl (*this))
+{
+}
+
+HighResolutionTimer::~HighResolutionTimer()
+{
+    stopTimer();
+}
+
+void HighResolutionTimer::startTimer (int periodMs)
+{
+    pimpl->start (jmax (1, periodMs));
+}
+
+void HighResolutionTimer::stopTimer()
+{
+    pimpl->stop();
+}
+
+bool HighResolutionTimer::isTimerRunning() const noexcept     { return getTimerInterval() != 0; }
+int HighResolutionTimer::getTimerInterval() const noexcept    { return pimpl->getPeriod(); }
 
 } // namespace juce

modules/juce_core/threads/juce_HighResolutionTimer.h

@@ -93,7 +93,7 @@ public:
     int getTimerInterval() const noexcept;
 
 private:
-    struct Pimpl;
+    class Pimpl;
     std::unique_ptr<Pimpl> pimpl;
 
     JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (HighResolutionTimer)

modules/juce_core/threads/juce_Process.h

@@ -50,7 +50,7 @@ public:
         @param priority     the process priority, where
                             0=low, 1=normal, 2=high, 3=realtime
     */
-    static void JUCE_CALLTYPE setPriority (const ProcessPriority priority);
+    static void JUCE_CALLTYPE setPriority (ProcessPriority priority);
 
     /** Kills the current process immediately.
 

modules/juce_core/threads/juce_Thread.cpp

@@ -22,9 +22,9 @@
 
 namespace juce
 {
-
+//==============================================================================
-Thread::Thread (const String& name, size_t stackSize)
+Thread::Thread (const String& name, size_t stackSize) : threadName (name),
-   : threadName (name), threadStackSize (stackSize)
+                                                        threadStackSize (stackSize)
 {
 }
 
@@ -81,12 +81,18 @@ void Thread::threadEntryPoint()
     const CurrentThreadHolder::Ptr currentThreadHolder (getCurrentThreadHolder());
     currentThreadHolder->value = this;
 
+   #if JUCE_ANDROID
+    setPriority (priority);
+   #endif
+
     if (threadName.isNotEmpty())
         setCurrentThreadName (threadName);
 
+    // This 'startSuspensionEvent' protects 'threadId' which is initialised after the platform's native 'CreateThread' method.
+    // This ensures it has been initialised correctly before it reaches this point.
     if (startSuspensionEvent.wait (10000))
     {
-        jassert (getCurrentThreadId() == threadId.get());
+        jassert (getCurrentThreadId() == threadId);
 
         if (affinityMask != 0)
             setCurrentThreadAffinityMask (affinityMask);
@@ -119,42 +125,65 @@ void JUCE_API juce_threadEntryPoint (void* userData)
 }
 
 //==============================================================================
-void Thread::startThread()
+bool Thread::startThreadInternal (Priority threadPriority)
 {
-    const ScopedLock sl (startStopLock);
+    shouldExit = false;
 
-    shouldExit = 0;
+    // 'priority' is essentially useless on Linux as only realtime
+    // has any options but we need to set this here to satsify
+    // later queries, otherwise we get inconsistent results across
+    // platforms.
+   #if JUCE_LINUX || JUCE_BSD
+    priority = threadPriority;
+   #endif
 
-    if (threadHandle.get() == nullptr)
+    if (createNativeThread (threadPriority))
     {
-        launchThread();
-        setThreadPriority (threadHandle.get(), threadPriority);
         startSuspensionEvent.signal();
+        return true;
     }
+
+    return false;
 }
 
-void Thread::startThread (int priority)
+bool Thread::startThread()
+{
+    return startThread (Priority::normal);
+}
+
+bool Thread::startThread (Priority threadPriority)
 {
     const ScopedLock sl (startStopLock);
 
-    if (threadHandle.get() == nullptr)
+    if (threadHandle == nullptr)
     {
-       #if JUCE_ANDROID
+        realtimeOptions.reset();
-        isAndroidRealtimeThread = (priority == realtimeAudioPriority);
+        return startThreadInternal (threadPriority);
-       #endif
+    }
 
-        threadPriority = getAdjustedPriority (priority);
+    return false;
-        startThread();
+}
-    }
+
-    else
+bool Thread::startRealtimeThread (const RealtimeOptions& options)
+{
+    const ScopedLock sl (startStopLock);
+
+    if (threadHandle == nullptr)
     {
-        setPriority (priority);
+        realtimeOptions = makeOptional (options);
+
+        if (startThreadInternal (Priority::normal))
+            return true;
+
+        realtimeOptions.reset();
     }
+
+    return false;
 }
 
 bool Thread::isThreadRunning() const
 {
-    return threadHandle.get() != nullptr;
+    return threadHandle != nullptr;
 }
 
 Thread* JUCE_CALLTYPE Thread::getCurrentThread()
@@ -164,19 +193,19 @@ Thread* JUCE_CALLTYPE Thread::getCurrentThread()
 
 Thread::ThreadID Thread::getThreadId() const noexcept
 {
-    return threadId.get();
+    return threadId;
 }
 
 //==============================================================================
 void Thread::signalThreadShouldExit()
 {
-    shouldExit = 1;
+    shouldExit = true;
     listeners.call ([] (Listener& l) { l.exitSignalSent(); });
 }
 
 bool Thread::threadShouldExit() const
 {
-    return shouldExit.get() != 0;
+    return shouldExit;
 }
 
 bool Thread::currentThreadShouldExit()
@@ -249,40 +278,9 @@ void Thread::removeListener (Listener* listener)
     listeners.remove (listener);
 }
 
-//==============================================================================
+bool Thread::isRealtime() const
-bool Thread::setPriority (int newPriority)
 {
-    newPriority = getAdjustedPriority (newPriority);
+    return realtimeOptions.hasValue();
-
-    // NB: deadlock possible if you try to set the thread prio from the thread itself,
-    // so using setCurrentThreadPriority instead in that case.
-    if (getCurrentThreadId() == getThreadId())
-        return setCurrentThreadPriority (newPriority);
-
-    const ScopedLock sl (startStopLock);
-
-   #if JUCE_ANDROID
-    bool isRealtime = (newPriority == realtimeAudioPriority);
-
-    // you cannot switch from or to an Android realtime thread once the
-    // thread is already running!
-    jassert (isThreadRunning() && (isRealtime == isAndroidRealtimeThread));
-
-    isAndroidRealtimeThread = isRealtime;
-   #endif
-
-    if ((! isThreadRunning()) || setThreadPriority (threadHandle.get(), newPriority))
-    {
-        threadPriority = newPriority;
-        return true;
-    }
-
-    return false;
-}
-
-bool Thread::setCurrentThreadPriority (const int newPriority)
-{
-    return setThreadPriority ({}, getAdjustedPriority (newPriority));
 }
 
 void Thread::setAffinityMask (const uint32 newAffinityMask)
@@ -290,11 +288,6 @@ void Thread::setAffinityMask (const uint32 newAffinityMask)
     affinityMask = newAffinityMask;
 }
 
-int Thread::getAdjustedPriority (int newPriority)
-{
-    return jlimit (0, 10, newPriority == realtimeAudioPriority ? 9 : newPriority);
-}
-
 //==============================================================================
 bool Thread::wait (const int timeOutMilliseconds) const
 {
@@ -349,7 +342,6 @@ bool JUCE_CALLTYPE Process::isRunningUnderDebugger() noexcept
     return juce_isRunningUnderDebugger();
 }
 
-
 //==============================================================================
 //==============================================================================
 #if JUCE_UNIT_TESTS

modules/juce_core/threads/juce_Thread.h

@@ -28,8 +28,8 @@ namespace juce
     Encapsulates a thread.
 
     Subclasses derive from Thread and implement the run() method, in which they
-    do their business. The thread can then be started with the startThread() method
+    do their business. The thread can then be started with the startThread() or
-    and controlled with various other methods.
+    startRealtimeThread() methods and controlled with various other methods.
 
     This class also contains some thread-related static methods, such
     as sleep(), yield(), getCurrentThreadId() etc.
@@ -42,6 +42,46 @@ namespace juce
 class JUCE_API  Thread
 {
 public:
+    //==============================================================================
+    /** The different runtime priorities of non-realtime threads.
+
+        @see startThread
+    */
+    enum class Priority
+    {
+        /** The highest possible priority that isn't a dedicated realtime thread. */
+        highest,
+
+        /** Makes use of performance cores and higher clocks. */
+        high,
+
+        /** The OS default. It will balance out across all cores. */
+        normal,
+
+        /** Uses efficiency cores when possible. */
+        low,
+
+        /** Restricted to efficiency cores on platforms that have them. */
+        background
+    };
+
+    //==============================================================================
+    /** A selection of options available when creating realtime threads.
+
+        @see startRealtimeThread
+    */
+    struct RealtimeOptions
+    {
+        /** Linux only: A value with a range of 0-10, where 10 is the highest priority. */
+        int priority = 5;
+
+        /* iOS/macOS only: A millisecond value representing the estimated time between each
+                           'Thread::run' call. Your thread may be penalised if you frequently
+                           overrun this.
+        */
+        uint32_t workDurationMs = 0;
+    };
+
     //==============================================================================
     /**
         Creates a thread.
@@ -78,23 +118,51 @@ public:
     virtual void run() = 0;
 
     //==============================================================================
-    /** Starts the thread running.
+    /** Attempts to start a new thread with default ('Priority::normal') priority.
 
         This will cause the thread's run() method to be called by a new thread.
         If this thread is already running, startThread() won't do anything.
 
+        If a thread cannot be created with the requested priority, this will return false
+        and Thread::run() will not be called. An exception to this is the Android platform,
+        which always starts a thread and attempts to upgrade the thread after creation.
+
+        @returns    true if the thread started successfully. false if it was unsuccesful.
+
         @see stopThread
     */
-    void startThread();
+    bool startThread();
 
-    /** Starts the thread with a given priority.
+    /** Attempts to start a new thread with a given priority.
 
-        Launches the thread with a given priority, where 0 = lowest, 10 = highest.
+        This will cause the thread's run() method to be called by a new thread.
-        If the thread is already running, its priority will be changed.
+        If this thread is already running, startThread() won't do anything.
 
-        @see startThread, setPriority, realtimeAudioPriority
+        If a thread cannot be created with the requested priority, this will return false
+        and Thread::run() will not be called. An exception to this is the Android platform,
+        which always starts a thread and attempts to upgrade the thread after creation.
+
+        @param newPriority    Priority the thread should be assigned. This parameter is ignored
+                              on Linux.
+
+        @returns    true if the thread started successfully, false if it was unsuccesful.
+
+        @see startThread, setPriority, startRealtimeThread
     */
-    void startThread (int priority);
+    bool startThread (Priority newPriority);
+
+    /** Starts the thread with realtime performance characteristics on platforms
+        that support it.
+
+        You cannot change the options of a running realtime thread, nor switch
+        a non-realtime thread to a realtime thread. To make these changes you must
+        first stop the thread and then restart with different options.
+
+        @param options    Realtime options the thread should be created with.
+
+        @see startThread, RealtimeOptions
+    */
+    bool startRealtimeThread (const RealtimeOptions& options);
 
     /** Attempts to stop the thread running.
 
@@ -198,50 +266,8 @@ public:
     /** Removes a listener added with addListener. */
     void removeListener (Listener*);
 
-    //==============================================================================
+    /** Returns true if this Thread represents a realtime thread. */
-    /** Special realtime audio thread priority
+    bool isRealtime() const;
-
-        This priority will create a high-priority thread which is best suited
-        for realtime audio processing.
-
-        Currently, this priority is identical to priority 9, except when building
-        for Android with OpenSL/Oboe support.
-
-        In this case, JUCE will ask OpenSL/Oboe to construct a super high priority thread
-        specifically for realtime audio processing.
-
-        Note that this priority can only be set **before** the thread has
-        started. Switching to this priority, or from this priority to a different
-        priority, is not supported under Android and will assert.
-
-        For best performance this thread should yield at regular intervals
-        and not call any blocking APIs.
-
-        @see startThread, setPriority, sleep, WaitableEvent
-     */
-    enum
-    {
-        realtimeAudioPriority = -1
-    };
-
-    /** Changes the thread's priority.
-
-        May return false if for some reason the priority can't be changed.
-
-        @param priority     the new priority, in the range 0 (lowest) to 10 (highest). A priority
-                            of 5 is normal.
-        @see realtimeAudioPriority
-    */
-    bool setPriority (int priority);
-
-    /** Changes the priority of the caller thread.
-
-        Similar to setPriority(), but this static method acts on the caller thread.
-        May return false if for some reason the priority can't be changed.
-
-        @see setPriority
-    */
-    static bool setCurrentThreadPriority (int priority);
 
     //==============================================================================
     /** Sets the affinity mask for the thread.
@@ -380,34 +406,58 @@ public:
     static void initialiseJUCE (void* jniEnv, void* jContext);
    #endif
 
+protected:
+    //==============================================================================
+    /** Returns the current priority of this thread.
+
+        This can only be called from the target thread. Doing so from another thread
+        will cause an assert.
+
+        @see setPriority
+    */
+    Priority getPriority() const;
+
+    /** Attempts to set the priority for this thread. Returns true if the new priority
+        was set successfully, false if not.
+
+        This can only be called from the target thread. Doing so from another thread
+        will cause an assert.
+
+        @param newPriority The new priority to be applied to the thread. Note: This
+                           has no effect on Linux platforms, subsequent calls to
+                           'getPriority' will return this value.
+
+        @see Priority
+    */
+    bool setPriority (Priority newPriority);
+
 private:
     //==============================================================================
     const String threadName;
-    Atomic<void*> threadHandle { nullptr };
+    std::atomic<void*> threadHandle { nullptr };
-    Atomic<ThreadID> threadId = {};
+    std::atomic<ThreadID> threadId { nullptr };
+    Optional<RealtimeOptions> realtimeOptions = {};
     CriticalSection startStopLock;
     WaitableEvent startSuspensionEvent, defaultEvent;
-    int threadPriority = 5;
     size_t threadStackSize;
     uint32 affinityMask = 0;
     bool deleteOnThreadEnd = false;
-    Atomic<int32> shouldExit { 0 };
+    std::atomic<bool> shouldExit { false };
     ListenerList<Listener, Array<Listener*, CriticalSection>> listeners;
 
-   #if JUCE_ANDROID
+   #if JUCE_ANDROID || JUCE_LINUX || JUCE_BSD
-    bool isAndroidRealtimeThread = false;
+    std::atomic<Priority> priority;
    #endif
 
    #ifndef DOXYGEN
     friend void JUCE_API juce_threadEntryPoint (void*);
    #endif
 
-    void launchThread();
+    bool startThreadInternal (Priority);
+    bool createNativeThread (Priority);
     void closeThreadHandle();
     void killThread();
     void threadEntryPoint();
-    static bool setThreadPriority (void*, int);
-    static int getAdjustedPriority (int);
 
     JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (Thread)
 };

modules/juce_core/threads/juce_ThreadPool.cpp

@@ -33,11 +33,14 @@ struct ThreadPool::ThreadPoolThread  : public Thread
     void run() override
     {
         while (! threadShouldExit())
+        {
             if (! pool.runNextJob (*this))
                 wait (500);
+        }
     }
 
     std::atomic<ThreadPoolJob*> currentJob { nullptr };
+
     ThreadPool& pool;
 
     JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (ThreadPoolThread)
@@ -90,16 +93,19 @@ ThreadPoolJob* ThreadPoolJob::getCurrentThreadPoolJob()
 }
 
 //==============================================================================
-ThreadPool::ThreadPool (int numThreads, size_t threadStackSize)
+ThreadPool::ThreadPool (int numThreads, size_t threadStackSize, Thread::Priority priority)
 {
     jassert (numThreads > 0); // not much point having a pool without any threads!
 
-    createThreads (numThreads, threadStackSize);
+    for (int i = jmax (1, numThreads); --i >= 0;)
+        threads.add (new ThreadPoolThread (*this, threadStackSize));
+
+    for (auto* t : threads)
+        t->startThread (priority);
 }
 
-ThreadPool::ThreadPool()
+ThreadPool::ThreadPool() : ThreadPool (SystemStats::getNumCpus(), 0, Thread::Priority::normal)
 {
-    createThreads (SystemStats::getNumCpus());
 }
 
 ThreadPool::~ThreadPool()
@@ -108,15 +114,6 @@ ThreadPool::~ThreadPool()
     stopThreads();
 }
 
-void ThreadPool::createThreads (int numThreads, size_t threadStackSize)
-{
-    for (int i = jmax (1, numThreads); --i >= 0;)
-        threads.add (new ThreadPoolThread (*this, threadStackSize));
-
-    for (auto* t : threads)
-        t->startThread();
-}
-
 void ThreadPool::stopThreads()
 {
     for (auto* t : threads)
@@ -330,17 +327,6 @@ StringArray ThreadPool::getNamesOfAllJobs (bool onlyReturnActiveJobs) const
     return s;
 }
 
-bool ThreadPool::setThreadPriorities (int newPriority)
-{
-    bool ok = true;
-
-    for (auto* t : threads)
-        if (! t->setPriority (newPriority))
-            ok = false;
-
-    return ok;
-}
-
 ThreadPoolJob* ThreadPool::pickNextJobToRun()
 {
     OwnedArray<ThreadPoolJob> deletionList;

modules/juce_core/threads/juce_ThreadPool.h

@@ -164,8 +164,9 @@ public:
         @param threadStackSize  the size of the stack of each thread. If this value
                                 is zero then the default stack size of the OS will
                                 be used.
+        @param priority         the desired priority of each thread in the pool.
     */
-    ThreadPool (int numberOfThreads, size_t threadStackSize = 0);
+    ThreadPool (int numberOfThreads, size_t threadStackSize = 0, Thread::Priority priority = Thread::Priority::normal);
 
     /** Creates a thread pool with one thread per CPU core.
         Once you've created a pool, you can give it some jobs by calling addJob().
@@ -309,13 +310,6 @@ public:
     */
     StringArray getNamesOfAllJobs (bool onlyReturnActiveJobs) const;
 
-    /** Changes the priority of all the threads.
-        This will call Thread::setPriority() for each thread in the pool.
-        May return false if for some reason the priority can't be changed.
-    */
-    bool setThreadPriorities (int newPriority);
-
-
 private:
     //==============================================================================
     Array<ThreadPoolJob*> jobs;
@@ -330,7 +324,6 @@ private:
     bool runNextJob (ThreadPoolThread&);
     ThreadPoolJob* pickNextJobToRun();
     void addToDeleteList (OwnedArray<ThreadPoolJob>&, ThreadPoolJob*) const;
-    void createThreads (int numThreads, size_t threadStackSize = 0);
     void stopThreads();
 
     // Note that this method has changed, and no longer has a parameter to indicate

modules/juce_events/interprocess/juce_ConnectedChildProcess.cpp

@@ -51,7 +51,7 @@ struct ChildProcessPingThread  : public Thread,
         pingReceived();
     }
 
-    void startPinging()                     { startThread (4); }
+    void startPinging()                     { startThread (Priority::low); }
 
     void pingReceived() noexcept            { countdown = timeoutMs / 1000 + 1; }
     void triggerConnectionLostMessage()     { triggerAsyncUpdate(); }

modules/juce_events/interprocess/juce_NetworkServiceDiscovery.cpp

@@ -41,7 +41,7 @@ NetworkServiceDiscovery::Advertiser::Advertiser (const String& serviceTypeUID,
     message.setAttribute ("address", String());
     message.setAttribute ("port", connectionPort);
 
-    startThread (2);
+    startThread (Priority::background);
 }
 
 NetworkServiceDiscovery::Advertiser::~Advertiser()
@@ -92,7 +92,7 @@ NetworkServiceDiscovery::AvailableServiceList::AvailableServiceList (const Strin
    #endif
 
     socket.bindToPort (broadcastPort);
-    startThread (2);
+    startThread (Priority::background);
 }
 
 NetworkServiceDiscovery::AvailableServiceList::~AvailableServiceList()

modules/juce_events/timers/juce_Timer.cpp

@@ -303,7 +303,7 @@ private:
 
     void handleAsyncUpdate() override
     {
-        startThread (7);
+        startThread (Priority::high);
     }
 
     JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (TimerThread)

modules/juce_gui_basics/filebrowser/juce_FileBrowserComponent.cpp

@@ -64,7 +64,7 @@ FileBrowserComponent::FileBrowserComponent (int flags_,
     }
 
     // The thread must be started before the DirectoryContentsList attempts to scan any file
-    thread.startThread (4);
+    thread.startThread (Thread::Priority::low);
 
     fileList.reset (new DirectoryContentsList (this, thread));
     fileList->setDirectory (currentRoot, true, true);

modules/juce_gui_basics/native/juce_win32_Windowing.cpp

@@ -1403,7 +1403,7 @@ public:
           monitor (mon)
     {
         listeners.push_back (listener);
-        startThread (10);
+        startThread (Priority::highest);
     }
 
     ~VSyncThread() override

modules/juce_gui_basics/windows/juce_ThreadWithProgressWindow.cpp

@@ -56,11 +56,11 @@ ThreadWithProgressWindow::~ThreadWithProgressWindow()
     stopThread (timeOutMsWhenCancelling);
 }
 
-void ThreadWithProgressWindow::launchThread (int priority)
+void ThreadWithProgressWindow::launchThread (Priority threadPriority)
 {
     JUCE_ASSERT_MESSAGE_THREAD
 
-    startThread (priority);
+    startThread (threadPriority);
     startTimer (100);
 
     {
@@ -105,9 +105,9 @@ void ThreadWithProgressWindow::timerCallback()
 void ThreadWithProgressWindow::threadComplete (bool) {}
 
 #if JUCE_MODAL_LOOPS_PERMITTED
-bool ThreadWithProgressWindow::runThread (const int priority)
+bool ThreadWithProgressWindow::runThread (Priority threadPriority)
 {
-    launchThread (priority);
+    launchThread (threadPriority);
 
     while (isTimerRunning())
         MessageManager::getInstance()->runDispatchLoopUntil (5);

modules/juce_gui_basics/windows/juce_ThreadWithProgressWindow.h

@@ -122,10 +122,10 @@ public:
         Before returning, the dialog box will be hidden.
 
         @param priority   the priority to use when starting the thread - see
-                          Thread::startThread() for values
+                          Thread::Priority for values
         @returns true if the thread finished normally; false if the user pressed cancel
     */
-    bool runThread (int priority = 5);
+    bool runThread (Priority Priority = Priority::normal);
    #endif
 
     /** Starts the thread and returns.
@@ -135,9 +135,9 @@ public:
         hidden and the threadComplete() method will be called.
 
         @param priority   the priority to use when starting the thread - see
-                          Thread::startThread() for values
+                          Thread::Priority for values
     */
-    void launchThread (int priority = 5);
+    void launchThread (Priority priority = Priority::normal);
 
     /** The thread should call this periodically to update the position of the progress bar.
 

modules/juce_product_unlocking/marketplace/juce_OnlineUnlockForm.cpp

@@ -58,7 +58,7 @@ struct OnlineUnlockForm::OverlayComp  : public Component,
             cancelButton->addListener (this);
         }
 
-        startThread (4);
+        startThread (Priority::normal);
     }
 
     ~OverlayComp() override