From ba2cd6cc34f934dd54b96687282a88a58ac675f3 Mon Sep 17 00:00:00 2001
From: reuk <reuk@users.noreply.github.com>
Date: Wed, 16 Jun 2021 18:12:24 +0100
Subject: [PATCH] IIRFilter:  Provide a new SingleThreadedIIRFilter which does
 not lock internally

---
 .../utilities/juce_IIRFilter.cpp              | 40 ++++++++-------
 .../utilities/juce_IIRFilter.h                | 51 ++++++++++++++++---
 2 files changed, 66 insertions(+), 25 deletions(-)

diff --git a/modules/juce_audio_basics/utilities/juce_IIRFilter.cpp b/modules/juce_audio_basics/utilities/juce_IIRFilter.cpp
index a1dc2526e2..fae0c9f961 100644
--- a/modules/juce_audio_basics/utilities/juce_IIRFilter.cpp
+++ b/modules/juce_audio_basics/utilities/juce_IIRFilter.cpp
@@ -258,42 +258,42 @@ IIRCoefficients IIRCoefficients::makePeakFilter (double sampleRate,
 }
 
 //==============================================================================
-IIRFilter::IIRFilter() noexcept
-{
-}
+template <typename Mutex>
+IIRFilterBase<Mutex>::IIRFilterBase() noexcept = default;
 
-IIRFilter::IIRFilter (const IIRFilter& other) noexcept  : active (other.active)
+template <typename Mutex>
+IIRFilterBase<Mutex>::IIRFilterBase (const IIRFilterBase& other) noexcept  : active (other.active)
 {
-    const SpinLock::ScopedLockType sl (other.processLock);
+    const typename Mutex::ScopedLockType sl (other.processLock);
     coefficients = other.coefficients;
 }
 
-IIRFilter::~IIRFilter() noexcept
-{
-}
-
 //==============================================================================
-void IIRFilter::makeInactive() noexcept
+template <typename Mutex>
+void IIRFilterBase<Mutex>::makeInactive() noexcept
 {
-    const SpinLock::ScopedLockType sl (processLock);
+    const typename Mutex::ScopedLockType sl (processLock);
     active = false;
 }
 
-void IIRFilter::setCoefficients (const IIRCoefficients& newCoefficients) noexcept
+template <typename Mutex>
+void IIRFilterBase<Mutex>::setCoefficients (const IIRCoefficients& newCoefficients) noexcept
 {
-    const SpinLock::ScopedLockType sl (processLock);
+    const typename Mutex::ScopedLockType sl (processLock);
     coefficients = newCoefficients;
     active = true;
 }
 
 //==============================================================================
-void IIRFilter::reset() noexcept
+template <typename Mutex>
+void IIRFilterBase<Mutex>::reset() noexcept
 {
-    const SpinLock::ScopedLockType sl (processLock);
+    const typename Mutex::ScopedLockType sl (processLock);
     v1 = v2 = 0.0;
 }
 
-float IIRFilter::processSingleSampleRaw (float in) noexcept
+template <typename Mutex>
+float IIRFilterBase<Mutex>::processSingleSampleRaw (float in) noexcept
 {
     auto out = coefficients.coefficients[0] * in + v1;
 
@@ -305,9 +305,10 @@ float IIRFilter::processSingleSampleRaw (float in) noexcept
     return out;
 }
 
-void IIRFilter::processSamples (float* const samples, const int numSamples) noexcept
+template <typename Mutex>
+void IIRFilterBase<Mutex>::processSamples (float* const samples, const int numSamples) noexcept
 {
-    const SpinLock::ScopedLockType sl (processLock);
+    const typename Mutex::ScopedLockType sl (processLock);
 
     if (active)
     {
@@ -333,4 +334,7 @@ void IIRFilter::processSamples (float* const samples, const int numSamples) noex
     }
 }
 
+template class IIRFilterBase<SpinLock>;
+template class IIRFilterBase<DummyCriticalSection>;
+
 } // namespace juce
diff --git a/modules/juce_audio_basics/utilities/juce_IIRFilter.h b/modules/juce_audio_basics/utilities/juce_IIRFilter.h
index 2246d87244..9f6dcc04c1 100644
--- a/modules/juce_audio_basics/utilities/juce_IIRFilter.h
+++ b/modules/juce_audio_basics/utilities/juce_IIRFilter.h
@@ -153,7 +153,8 @@ public:
 
     @tags{Audio}
 */
-class JUCE_API  IIRFilter
+template <typename Mutex>
+class JUCE_API  IIRFilterBase
 {
 public:
     //==============================================================================
@@ -163,13 +164,10 @@ public:
         you process with it. Use the setCoefficients() method to turn it into the
         type of filter needed.
     */
-    IIRFilter() noexcept;
+    IIRFilterBase() noexcept;
 
     /** Creates a copy of another filter. */
-    IIRFilter (const IIRFilter&) noexcept;
-
-    /** Destructor. */
-    ~IIRFilter() noexcept;
+    IIRFilterBase (const IIRFilterBase&) noexcept;
 
     //==============================================================================
     /** Clears the filter so that any incoming data passes through unchanged. */
@@ -202,7 +200,7 @@ public:
 
 protected:
     //==============================================================================
-    SpinLock processLock;
+    Mutex processLock;
     IIRCoefficients coefficients;
     float v1 = 0, v2 = 0;
     bool active = false;
@@ -214,4 +212,43 @@ protected:
     JUCE_LEAK_DETECTOR (IIRFilter)
 };
 
+/**
+    An IIR filter that can perform low, high, or band-pass filtering on an
+    audio signal, and which attempts to implement basic thread-safety.
+
+    This class synchronises calls to some of its member functions, making it
+    safe (although not necessarily real-time-safe) to reset the filter or
+    apply new coefficients while the filter is processing on another thread.
+    In most cases this style of internal locking should not be used, and you
+    should attempt to provide thread-safety at a higher level in your program.
+    If you can guarantee that calls to the filter will be synchronised externally,
+    you could consider switching to SingleThreadedIIRFilter instead.
+
+    @see SingleThreadedIIRFilter, IIRCoefficient, IIRFilterAudioSource
+
+    @tags{Audio}
+*/
+class IIRFilter : public IIRFilterBase<SpinLock>
+{
+public:
+    using IIRFilterBase::IIRFilterBase;
+};
+
+/**
+    An IIR filter that can perform low, high, or band-pass filtering on an
+    audio signal, with no thread-safety guarantees.
+
+    You should use this class if you need an IIR filter, and don't plan to
+    call its member functions from multiple threads at once.
+
+    @see IIRFilter, IIRCoefficient, IIRFilterAudioSource
+
+    @tags{Audio}
+*/
+class SingleThreadedIIRFilter : public IIRFilterBase<DummyCriticalSection>
+{
+public:
+    using IIRFilterBase::IIRFilterBase;
+};
+
 } // namespace juce