From 32b9b1e9db018a020c2a1e83d4592466e1078e8c Mon Sep 17 00:00:00 2001
From: ed <eddavies95@gmail.com>
Date: Fri, 23 Oct 2020 10:52:27 +0100
Subject: [PATCH] CoreAudio:  Prevent audio glitches before microphone
 permission granted

If input channels have been requested but no data is being sent from CoreAudio (usually due to permissions not being granted yet) then avoid waiting unnecessarily in AudioIODeviceCombiner::readInput() which could previously cause audio glitches. Also changed the wait time to use an exponential backoff.
---
 .../native/juce_mac_CoreAudio.cpp             | 30 ++++++++++++++-----
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/modules/juce_audio_devices/native/juce_mac_CoreAudio.cpp b/modules/juce_audio_devices/native/juce_mac_CoreAudio.cpp
index 646aae7c7e..8d6776411a 100644
--- a/modules/juce_audio_devices/native/juce_mac_CoreAudio.cpp
+++ b/modules/juce_audio_devices/native/juce_mac_CoreAudio.cpp
@@ -1663,11 +1663,16 @@ private:
     void readInput (AudioBuffer<float>& buffer, const int numSamples, const int blockSizeMs)
     {
         for (auto* d : devices)
-            d->done = (d->numInputChans == 0);
+            d->done = (d->numInputChans == 0 || d->isWaitingForInput);
 
-        for (int tries = 5;;)
+        float totalWaitTimeMs = blockSizeMs * 5.0f;
+        constexpr int numReadAttempts = 6;
+        auto sumPower2s = [] (int maxPower) { return (1 << (maxPower + 1)) - 1; };
+        float waitTime = totalWaitTimeMs / (float) sumPower2s (numReadAttempts - 2);
+
+        for (int numReadAttemptsRemaining = numReadAttempts;;)
         {
-            bool anyRemaining = false;
+            bool anySamplesRemaining = false;
 
             for (auto* d : devices)
             {
@@ -1679,17 +1684,20 @@ private:
                         d->done = true;
                     }
                     else
-                        anyRemaining = true;
+                    {
+                        anySamplesRemaining = true;
+                    }
                 }
             }
 
-            if (! anyRemaining)
+            if (! anySamplesRemaining)
                 return;
 
-            if (--tries == 0)
+            if (--numReadAttemptsRemaining == 0)
                 break;
 
-            wait (blockSizeMs);
+            wait (jmax (1, roundToInt (waitTime)));
+            waitTime *= 2.0f;
         }
 
         for (auto* d : devices)
@@ -1717,7 +1725,9 @@ private:
                         d->done = true;
                     }
                     else
+                    {
                         anyRemaining = true;
+                    }
                 }
             }
 
@@ -1808,6 +1818,8 @@ private:
             numInputChans  = useInputs  ? device->getActiveInputChannels().countNumberOfSetBits()  : 0;
             numOutputChans = useOutputs ? device->getActiveOutputChannels().countNumberOfSetBits() : 0;
 
+            isWaitingForInput = numInputChans > 0;
+
             inputIndex = channelIndex;
             outputIndex = channelIndex + numInputChans;
 
@@ -1892,6 +1904,8 @@ private:
         {
             if (numInputChannels > 0)
             {
+                isWaitingForInput = false;
+
                 int start1, size1, start2, size2;
                 inputFifo.prepareToWrite (numSamples, start1, size1, start2, size2);
 
@@ -1972,7 +1986,7 @@ private:
         AudioIODeviceCombiner& owner;
         std::unique_ptr<CoreAudioIODevice> device;
         int inputIndex = 0, numInputChans = 0, outputIndex = 0, numOutputChans = 0;
-        bool useInputs = false, useOutputs = false;
+        bool useInputs = false, useOutputs = false, isWaitingForInput = false;
         AbstractFifo inputFifo { 32 }, outputFifo { 32 };
         bool done = false;