APVTS: Use atomic floats for current parameter states

BREAKING-CHANGES.txt

@@ -4,11 +4,33 @@ JUCE breaking changes
 Develop
 =======
 
+Change
+------
+AudioProcessorValueTreeState::getRawParameterValue now returns a
+std::atomic<float>* instead of a float*.
+
+Possible Issues
+---------------
+Existing code which explicitly mentions the type of the returned value, or
+interacts with the dereferenced float in ways unsupported by the std::atomic
+wrapper, will fail to compile. Certain evaluation-reordering compiler
+optimisations may no longer be possible.
+
+Workaround
+----------
+Update your code to deal with a std::atomic<float>* instead of a float*.
+
+Rationale
+---------
+Returning a std::atomic<float>* allows the JUCE framework to have much stronger
+guarantees about thread safety.
+
+
 Change
 ------
 Removed a workaround from the ASIOAudioIODevice::getOutputLatencyInSamples()
-and ASIOAudioIODevice::getInputLatencyInSamples() methods which was adding
-an arbitrary amount to the reported latencies to compensate for dodgy, old
+and ASIOAudioIODevice::getInputLatencyInSamples() methods which was adding an
+arbitrary amount to the reported latencies to compensate for dodgy, old
 drivers.
 
 Possible Issues
@@ -17,8 +39,8 @@ Code which relied on these altered values may now behave differently.
 
 Workaround
 ----------
-Update your code to deal with the new, correct values reported from the
-drivers directly.
+Update your code to deal with the new, correct values reported from the drivers
+directly.
 
 Rationale
 ---------
@@ -37,8 +59,8 @@ Possible Issues
 AudioProcessor subclasses which have overridden the default implementations of
 get/setProgramStateInformation (which simply call through to
 get/setStateInformation) may be unable to load previously saved state; state
-previously saved via a call to getProgramStateInformation will be presented
-to setStateInformation.
+previously saved via a call to getProgramStateInformation will be presented to
+setStateInformation.
 
 Workaround
 ----------

modules/juce_audio_processors/utilities/juce_AudioProcessorValueTreeState.cpp

@@ -124,8 +124,8 @@ public:
         return parameter.getText (normalise (value), 0);
     }
 
-    float getDenormalisedValue() const   { return unnormalisedValue; }
-    float& getRawDenormalisedValue()     { return unnormalisedValue; }
+    float getDenormalisedValue() const                { return unnormalisedValue; }
+    std::atomic<float>& getRawDenormalisedValue()     { return unnormalisedValue; }
 
     bool flushToTree (const Identifier& key, UndoManager* um)
     {
@@ -139,12 +139,12 @@ public:
             if ((float) *valueProperty != unnormalisedValue)
             {
                 ScopedValueSetter<bool> svs (ignoreParameterChangedCallbacks, true);
-                tree.setProperty (key, unnormalisedValue, um);
+                tree.setProperty (key, unnormalisedValue.load(), um);
             }
         }
         else
         {
-            tree.setProperty (key, unnormalisedValue, nullptr);
+            tree.setProperty (key, unnormalisedValue.load(), nullptr);
         }
 
         return true;
@@ -188,7 +188,7 @@ private:
 
     RangedAudioParameter& parameter;
     ListenerList<Listener> listeners;
-    float unnormalisedValue{};
+    std::atomic<float> unnormalisedValue{};
     std::atomic<bool> needsUpdate { true };
     bool listenersNeedCalling { true }, ignoreParameterChangedCallbacks { false };
 };
@@ -355,7 +355,7 @@ RangedAudioParameter* AudioProcessorValueTreeState::getParameter (StringRef para
     return nullptr;
 }
 
-float* AudioProcessorValueTreeState::getRawParameterValue (StringRef paramID) const noexcept
+std::atomic<float>* AudioProcessorValueTreeState::getRawParameterValue (StringRef paramID) const noexcept
 {
     if (auto* p = getParameterAdapter (paramID))
         return &p->getRawDenormalisedValue();
@@ -791,7 +791,7 @@ struct ParameterAdapterTests  : public UnitTest
                 adapter.setDenormalisedValue (value);
 
                 expectEquals (adapter.getDenormalisedValue(), value);
-                expectEquals (adapter.getRawDenormalisedValue(), value);
+                expectEquals (adapter.getRawDenormalisedValue().load(), value);
             };
 
             test ({ -20, -10 }, -15);
@@ -1044,7 +1044,7 @@ public:
             const auto value = 0.5f;
             param->setValueNotifyingHost (value);
 
-            expectEquals (*proc.state.getRawParameterValue (key), value);
+            expectEquals (proc.state.getRawParameterValue (key)->load(), value);
         }
 
         beginTest ("After adding an APVTS::Parameter, its value is the default value");
@@ -1062,7 +1062,7 @@ public:
                 nullptr,
                 nullptr));
 
-            expectEquals (*proc.state.getRawParameterValue (key), value);
+            expectEquals (proc.state.getRawParameterValue (key)->load(), value);
         }
 
         beginTest ("Listeners receive notifications when parameters change");
@@ -1138,7 +1138,7 @@ public:
             value = newValue;
 
             expectEquals (param->getValue(), newValue);
-            expectEquals (*proc.state.getRawParameterValue (key), newValue);
+            expectEquals (proc.state.getRawParameterValue (key)->load(), newValue);
         }
 
         beginTest ("When the parameter value is changed, custom parameter values are updated");
@@ -1154,7 +1154,7 @@ public:
             value = newValue;
 
             expectEquals (paramPtr->getCurrentChoiceName(), choices[int (newValue)]);
-            expectEquals (*proc.state.getRawParameterValue (key), newValue);
+            expectEquals (proc.state.getRawParameterValue (key)->load(), newValue);
         }
 
         beginTest ("When the parameter value is changed, listeners are notified");

modules/juce_audio_processors/utilities/juce_AudioProcessorValueTreeState.h

@@ -285,7 +285,7 @@ public:
         Note that calling this method from within AudioProcessorValueTreeState::Listener::parameterChanged()
         is not guaranteed to return an up-to-date value for the parameter.
     */
-    float* getRawParameterValue (StringRef parameterID) const noexcept;
+    std::atomic<float>* getRawParameterValue (StringRef parameterID) const noexcept;
 
     //==============================================================================
     /** A listener class that can be attached to an AudioProcessorValueTreeState.