From d246cc280df7b5098bf87f0c627e95465d9b18d1 Mon Sep 17 00:00:00 2001
From: attila <attila@juce.com>
Date: Tue, 28 Jun 2022 16:48:08 +0200
Subject: [PATCH] MessageManager:  Add mutex to isThisTheMessageThread() and
 setCurrentThreadAsMessageThread()

---
 modules/juce_events/messages/juce_MessageManager.cpp | 8 +++++---
 modules/juce_events/messages/juce_MessageManager.h   | 1 +
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/modules/juce_events/messages/juce_MessageManager.cpp b/modules/juce_events/messages/juce_MessageManager.cpp
index 153ac62470..cca2d4925a 100644
--- a/modules/juce_events/messages/juce_MessageManager.cpp
+++ b/modules/juce_events/messages/juce_MessageManager.cpp
@@ -225,6 +225,8 @@ void MessageManager::deregisterBroadcastListener (ActionListener* const listener
 //==============================================================================
 bool MessageManager::isThisTheMessageThread() const noexcept
 {
+    const std::lock_guard<std::mutex> lock { messageThreadIdMutex };
+
     return Thread::getCurrentThreadId() == messageThreadId;
 }
 
@@ -232,10 +234,10 @@ void MessageManager::setCurrentThreadAsMessageThread()
 {
     auto thisThread = Thread::getCurrentThreadId();
 
-    if (messageThreadId != thisThread)
-    {
-        messageThreadId = thisThread;
+    const std::lock_guard<std::mutex> lock { messageThreadIdMutex };
 
+    if (std::exchange (messageThreadId, thisThread) != thisThread)
+    {
        #if JUCE_WINDOWS
         // This is needed on windows to make sure the message window is created by this thread
         doPlatformSpecificShutdown();
diff --git a/modules/juce_events/messages/juce_MessageManager.h b/modules/juce_events/messages/juce_MessageManager.h
index 9a5c26e697..8687a057cf 100644
--- a/modules/juce_events/messages/juce_MessageManager.h
+++ b/modules/juce_events/messages/juce_MessageManager.h
@@ -328,6 +328,7 @@ private:
     Atomic<int> quitMessagePosted { 0 }, quitMessageReceived { 0 };
     Thread::ThreadID messageThreadId;
     Atomic<Thread::ThreadID> threadWithLock;
+    mutable std::mutex messageThreadIdMutex;
 
     static bool postMessageToSystemQueue (MessageBase*);
     static void* exitModalLoopCallback (void*);