Fixed a bug where ThreadLocalValue would inadvertently share its value between different instances of the same Type

modules/juce_core/system/juce_CompilerSupport.h

@@ -44,6 +44,7 @@
 
  #if (__GNUC__ * 100 + __GNUC_MINOR__) >= 406
   #define JUCE_STDLIB_HAS_STD_FUNCTION_SUPPORT 1
+  #define JUCE_COMPILER_SUPPORTS_THREAD_LOCAL 1
  #endif
 
  #ifndef JUCE_EXCEPTIONS_DISABLED
@@ -67,6 +68,7 @@
 
  #if (defined (_LIBCPP_VERSION) || ! (JUCE_MAC || JUCE_IOS))
   #define JUCE_STDLIB_HAS_STD_FUNCTION_SUPPORT 1
+  #define JUCE_COMPILER_SUPPORTS_THREAD_LOCAL 1
  #endif
 
  #if __has_feature (cxx_generalized_initializers) && (defined (_LIBCPP_VERSION) || ! (JUCE_MAC || JUCE_IOS))
@@ -106,6 +108,7 @@
   #define JUCE_COMPILER_SUPPORTS_VARIADIC_TEMPLATES 1
   #define JUCE_DELETED_FUNCTION = delete
   #define JUCE_STDLIB_HAS_STD_FUNCTION_SUPPORT 1
+  #define JUCE_COMPILER_SUPPORTS_THREAD_LOCAL 1
  #endif
 
  #if _MSC_VER >= 1900

modules/juce_core/threads/juce_Thread.cpp

@@ -277,9 +277,9 @@ bool JUCE_CALLTYPE Process::isRunningUnderDebugger() noexcept
     return juce_isRunningUnderDebugger();
 }
 
-//==============================================================================
 #if JUCE_UNIT_TESTS
 
+//==============================================================================
 class AtomicTests  : public UnitTest
 {
 public:
@@ -401,4 +401,60 @@ public:
 
 static AtomicTests atomicUnitTests;
 
+//==============================================================================
+class ThreadLocalValueUnitTest : public UnitTest, private Thread
+{
+public:
+    ThreadLocalValueUnitTest()
+        : UnitTest ("ThreadLocalValue"),
+          Thread ("ThreadLocalValue Thread")
+    {}
+
+    void runTest() override
+    {
+        beginTest ("values are thread local");
+
+        {
+            ThreadLocalValue<int> threadLocal;
+
+            sharedThreadLocal = &threadLocal;
+
+            sharedThreadLocal.get()->get() = 1;
+
+            startThread();
+            signalThreadShouldExit();
+            waitForThreadToExit (-1);
+
+            mainThreadResult = sharedThreadLocal.get()->get();
+
+            expectEquals (mainThreadResult.get(), 1);
+            expectEquals (auxThreadResult.get(), 2);
+        }
+
+        beginTest ("values are per-instance");
+
+        {
+            ThreadLocalValue<int> a, b;
+
+            a.get() = 1;
+            b.get() = 2;
+
+            expectEquals (a.get(), 1);
+            expectEquals (b.get(), 2);
+        }
+    }
+
+private:
+    Atomic<int> mainThreadResult, auxThreadResult;
+    Atomic<ThreadLocalValue<int>*> sharedThreadLocal;
+
+    void run() override
+    {
+        sharedThreadLocal.get()->get() = 2;
+        auxThreadResult = sharedThreadLocal.get()->get();
+    }
+};
+
+ThreadLocalValueUnitTest threadLocalValueUnitTest;
+
 #endif

modules/juce_core/threads/juce_ThreadLocalValue.h

@@ -22,13 +22,6 @@
 
 #pragma once
 
-// (NB: on win32, native thread-locals aren't possible in a dynamically loaded DLL in XP).
-#if ! ((JUCE_MSVC && (JUCE_64BIT || ! defined (JucePlugin_PluginCode))) \
-       || (JUCE_MAC && JUCE_CLANG && defined (MAC_OS_X_VERSION_10_7) \
-             && MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_7))
- #define JUCE_NO_COMPILER_THREAD_LOCAL 1
-#endif
-
 //==============================================================================
 /**
     Provides cross-platform support for thread-local objects.
@@ -61,7 +54,7 @@ public:
     */
     ~ThreadLocalValue()
     {
-       #if JUCE_NO_COMPILER_THREAD_LOCAL
+       #if ! JUCE_COMPILER_SUPPORTS_THREAD_LOCAL
         for (ObjectHolder* o = first.value; o != nullptr;)
         {
             ObjectHolder* const next = o->next;
@@ -102,7 +95,10 @@ public:
     */
     Type& get() const noexcept
     {
-       #if JUCE_NO_COMPILER_THREAD_LOCAL
+       #if JUCE_COMPILER_SUPPORTS_THREAD_LOCAL
+        static thread_local HashMap<const void*, Type> holder;
+        return holder.getReference (this);
+       #else
         const Thread::ThreadID threadId = Thread::getCurrentThreadId();
 
         for (ObjectHolder* o = first.get(); o != nullptr; o = o->next)
@@ -136,12 +132,6 @@ public:
         while (! first.compareAndSetBool (newObject, newObject->next));
 
         return newObject->object;
-       #elif JUCE_MAC
-        static __thread Type object;
-        return object;
-       #elif JUCE_MSVC
-        static __declspec(thread) Type object;
-        return object;
        #endif
     }
 
@@ -150,7 +140,7 @@ public:
     */
     void releaseCurrentThreadStorage()
     {
-       #if JUCE_NO_COMPILER_THREAD_LOCAL
+       #if ! JUCE_COMPILER_SUPPORTS_THREAD_LOCAL
         const Thread::ThreadID threadId = Thread::getCurrentThreadId();
 
         for (ObjectHolder* o = first.get(); o != nullptr; o = o->next)
@@ -166,7 +156,7 @@ public:
 
 private:
     //==============================================================================
-   #if JUCE_NO_COMPILER_THREAD_LOCAL
+   #if ! JUCE_COMPILER_SUPPORTS_THREAD_LOCAL
     struct ObjectHolder
     {
         ObjectHolder (const Thread::ThreadID& tid)