Allow canceling arbitrary active decoders

Sources/CSFBAudioEngine/Player/AudioPlayerNode.h

@@ -205,6 +205,7 @@ class AudioPlayerNode final {
 
 	Decoder _Nullable CurrentDecoder() const noexcept;
 	void CancelActiveDecoders(bool cancelAllActive) noexcept;
+	bool CancelActiveDecoder(Decoder _Nonnull decoder) noexcept;
 
 private:
 #pragma mark - Decoding

Sources/CSFBAudioEngine/Player/AudioPlayerNode.mm

@@ -657,6 +657,23 @@ bool PerformSeekIfRequired() noexcept
 	}
 }
 
+bool SFB::AudioPlayerNode::CancelActiveDecoder(Decoder _Nonnull decoder) noexcept
+{
+#if DEBUG
+	assert(decoder != nil);
+#endif /* DEBUG */
+
+	std::lock_guard<SFB::UnfairLock> lock(mDecoderLock);
+	const auto iter = std::find_if(mActiveDecoders.cbegin(), mActiveDecoders.cend(), [&decoder](const auto& decoderState){
+		return decoderState->mDecoder == decoder;
+	});
+	if(iter == mActiveDecoders.cend())
+		return false;
+	(*iter)->mFlags.fetch_or(DecoderState::eFlagCancelRequested, std::memory_order_acq_rel);
+	mDecodingSemaphore.Signal();
+	return true;
+}
+
 #pragma mark - Decoding
 
 void SFB::AudioPlayerNode::ProcessDecoders(std::stop_token stoken) noexcept

Sources/CSFBAudioEngine/Player/SFBAudioPlayerNode.mm

@@ -158,6 +158,12 @@ - (void)cancelActiveDecoders
 	_node->CancelActiveDecoders(true);
 }
 
+- (BOOL)cancelActiveDecoder:(id<SFBPCMDecoding>)decoder
+{
+	NSParameterAssert(decoder != nil);
+	return _node->CancelActiveDecoder(decoder);
+}
+
 // AVAudioNode override
 - (void)reset
 {

Sources/CSFBAudioEngine/include/SFBAudioEngine/SFBAudioPlayerNode.h

@@ -127,6 +127,10 @@ NS_SWIFT_NAME(AudioPlayerNode) @interface SFBAudioPlayerNode : AVAudioSourceNode
 /// A transition period occurs when decoder *A* has completed decoding but not yet completed rendering
 /// and decoder *B* has started decoding but not yet started rendering.
 - (void)cancelActiveDecoders;
+/// Cancels an active decoder
+/// - parameter decoder: The decoder to cancel
+/// - returns: `YES` if the decoder was canceled successfully
+- (BOOL)cancelActiveDecoder:(id<SFBPCMDecoding>)decoder;
 
 #pragma mark - Playback Control