AudioWorkgroups: Add os_workgroup_max_parallel_threads support

modules/juce_audio_basics/utilities/juce_AudioWorkgroup.cpp

@@ -204,6 +204,21 @@ void AudioWorkgroup::join (WorkgroupToken& token) const
     token.reset();
 }
 
+size_t AudioWorkgroup::getMaxParallelThreadCount() const
+{
+   #if JUCE_AUDIOWORKGROUP_TYPES_AVAILABLE
+
+    if (@available (macos 11.0, ios 14.0, *))
+    {
+        if (auto wg = WorkgroupProvider::getWorkgroup (*this))
+            return (size_t) os_workgroup_max_parallel_threads (wg, nullptr);
+    }
+
+   #endif
+
+   return 0;
+}
+
 AudioWorkgroup::operator bool() const { return WorkgroupProvider::getWorkgroup (*this) != nullptr; }
 
 #if JUCE_AUDIOWORKGROUP_TYPES_AVAILABLE

modules/juce_audio_basics/utilities/juce_AudioWorkgroup.h

@@ -203,6 +203,13 @@ public:
     */
     void reset() { erased = nullptr; }
 
+    /** Returns the recommended maximum number of parallel threads that should join this workgroup.
+
+        This recommendation is based on the workgroup attributes and current hardware, but not on
+        system load. On a very busy system, it may be more effective to use fewer parallel threads.
+    */
+    size_t getMaxParallelThreadCount() const;
+
 private:
     const WorkgroupProvider* getWorkgroupProvider() const { return erased != nullptr ? erased() : nullptr; }