Implement RenderMeasurer

RenderMeasurer measures CPU load of given audio unit. It can be used for
user facing CPU meter, but also for automated performance testing.

Author: jcavar

Sources/AudioKitEX/Nodes/RenderMeasurer.swift

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+// Copyright AudioKit. All Rights Reserved. Revision History at http://github.com/AudioKit/AudioKit/
+
+import AVFAudio
+import CAudioKitEX
+
+/// A class to measure the proportion of buffer time
+/// audio unit is spending in its render block
+/// It can be used to measure CPU usage of the whole audio chain
+/// by attaching it to `AVAudioEngine.outputNode`,
+/// as well as any other audio unit.
+public class RenderMeasurer {
+    private let renderMeasurer = akRenderMeasurerCreate()
+    private let node: AUAudioUnit
+    private let token: Int
+    private let timebaseRatio: Double
+
+    public init(node: AUAudioUnit) {
+        self.node = node
+        var timebase = mach_timebase_info_data_t(numer: 0, denom: 0)
+        let status = mach_timebase_info(&timebase)
+        assert(status == 0)
+        timebaseRatio = Double(timebase.numer) / Double(timebase.denom)
+        let observer = akRenderMeasurerCreateObserver(renderMeasurer)
+        self.token = node.token(byAddingRenderObserver: observer!)
+    }
+
+    deinit {
+        node.removeRenderObserver(token)
+    }
+
+    /// Returns the proportion of buffer time
+    /// audio unit is spending in its render block
+    /// This is usually number between 0 - 1, but
+    /// it can be higher in case of dropouts
+    public func usage() -> Double {
+        let sampleRate = node.outputBusses[0].format.sampleRate
+        let currentUsage = akRenderMeasurerGetUsage(renderMeasurer)
+        return Double(currentUsage) * timebaseRatio * sampleRate / 1_000_000_000
+    }
+}

Sources/CAudioKitEX/Nodes/RenderMeasurerDSP.mm

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+// Copyright AudioKit. All Rights Reserved. Revision History at http://github.com/AudioKit/AudioKit/
+
+#include "DSPBase.h"
+#import "CAudioKit.h"
+#include <mach/mach_time.h>
+#include "RenderMeasurer.h"
+
+struct RenderMeasurer {
+
+public:
+    RenderMeasurer() {
+        usage = 0;
+    }
+
+    static RenderMeasurer *_Nonnull create() {
+        RenderMeasurer* measurer = new RenderMeasurer();
+        return measurer;
+    }
+
+    _Nonnull AURenderObserver createObserver() {
+        auto sharedThis = std::shared_ptr<RenderMeasurer>(this);
+        return ^void(AudioUnitRenderActionFlags actionFlags,
+                     const AudioTimeStamp *timestamp,
+                     AUAudioFrameCount frameCount,
+                     NSInteger outputBusNumber)
+        {
+            uint64 time = mach_absolute_time();
+            if (actionFlags == kAudioUnitRenderAction_PreRender) {
+                sharedThis->startTime = time;
+                return;
+            }
+            uint64 endTime = time;
+            sharedThis->usage.store((double)(endTime - sharedThis->startTime) / (double)frameCount);
+        };
+    }
+
+    double currentUsage() {
+        return usage.load();
+    }
+
+private:
+    std::atomic<double> usage;
+    uint64 startTime;
+};
+
+RenderMeasurerRef akRenderMeasurerCreate(void) {
+    return new RenderMeasurer();
+}
+
+AURenderObserver akRenderMeasurerCreateObserver(RenderMeasurerRef measurer) {
+    return measurer->createObserver();
+}
+
+double akRenderMeasurerGetUsage(RenderMeasurerRef measurer) {
+    return measurer->currentUsage();
+}

Sources/CAudioKitEX/include/RenderMeasurer.h

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+// Copyright AudioKit. All Rights Reserved. Revision History at http://github.com/AudioKit/AudioKit/
+
+#pragma once
+
+#include <AudioUnit/AudioUnit.h>
+
+typedef struct RenderMeasurer* RenderMeasurerRef;
+
+CF_EXTERN_C_BEGIN
+
+RenderMeasurerRef akRenderMeasurerCreate(void);
+AURenderObserver akRenderMeasurerCreateObserver(RenderMeasurerRef measurer);
+double akRenderMeasurerGetUsage(RenderMeasurerRef measurer);
+
+CF_EXTERN_C_END

Tests/AudioKitEXTests/RenderMeasurerTests.swift

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+// Copyright AudioKit. All Rights Reserved. Revision History at http://github.com/AudioKit/AudioKit/
+
+import AudioKit
+import AudioKitEX
+import XCTest
+import AVFAudio
+import CAudioKitEX
+
+class RenderMeasurerTests: XCTestCase {
+    let engine = AVAudioEngine()
+    var sleepProporition: Float = 1
+    lazy var source = AVAudioSourceNode { _, _, frameCount, _ -> OSStatus in
+        usleep(UInt32(Float(frameCount) / 44100 * 1000 * 1000 * self.sleepProporition))
+        return noErr
+    }
+
+    override func setUp() {
+        engine.attach(source)
+        engine.connect(source, to: engine.mainMixerNode, format: nil)
+        try! engine.start()
+    }
+
+    override func tearDown() {
+        engine.stop()
+    }
+
+    func testUsageHigherThen1() async throws {
+        self.sleepProporition = 1
+        let measurer = RenderMeasurer(node: source.auAudioUnit)
+        for _ in 1...10 {
+            try await Task.sleep(nanoseconds: 1_000_000_00)
+            XCTAssertGreaterThanOrEqual(measurer.usage(), 1)
+        }
+    }
+
+    func testUsageHigherThen05() async throws {
+        self.sleepProporition = 0.5
+        let measurer = RenderMeasurer(node: source.auAudioUnit)
+        for _ in 1...10 {
+            try await Task.sleep(nanoseconds: 1_000_000_00)
+            let usage = measurer.usage()
+            XCTAssertGreaterThanOrEqual(usage, 0.5)
+            XCTAssertLessThanOrEqual(usage, 1)
+        }
+    }
+}