Ticket #58551: dcb6c57df2fc.txt

# HG changeset patch
# User Ryan C. Gordon <icculus@icculus.org>
# Date 1553531078 14400
# Node ID dcb6c57df2fc8fbf5b82d04782322f64658a5e0b
# Parent  36ee991073903add82a71be51943e3b650558c5a
Backed out changeset ffd52bb02bcc

This was meant to migrate CoreAudio onto the same SDL_RunAudio() path that
most other audio drivers are on, but it introduced a bug because it doesn't
deal with dropped audio buffers...and fixing that properly just introduces
latency.

I might revisit this later, perhaps by reworking SDL_RunAudio to allow for
this sort of API better, or redesigning the whole subsystem or something, I
don't know. I'm not super-thrilled that this has to exist outside of the usual
codepaths, though.

Fixes Bugzilla #4481.

diff -r 36ee99107390 -r dcb6c57df2fc src/audio/SDL_audio.c
--- a/src/audio/SDL_audio.c     Thu Mar 21 10:39:49 2019 -0400
+++ b/src/audio/SDL_audio.c     Mon Mar 25 12:24:38 2019 -0400
@@ -896,8 +896,6 @@
         }
     }
 
-    current_audio.impl.PrepareToClose(device);
-
     current_audio.impl.FlushCapture(device);
 
     current_audio.impl.ThreadDeinit(device);
diff -r 36ee99107390 -r dcb6c57df2fc src/audio/coreaudio/SDL_coreaudio.h
--- a/src/audio/coreaudio/SDL_coreaudio.h       Thu Mar 21 10:39:49 2019 -0400
+++ b/src/audio/coreaudio/SDL_coreaudio.h       Mon Mar 25 12:24:38 2019 -0400
@@ -45,14 +45,16 @@
 
 struct SDL_PrivateAudioData
 {
+    SDL_Thread *thread;
     AudioQueueRef audioQueue;
-    int numAudioBuffers;
     AudioQueueBufferRef *audioBuffer;
     void *buffer;
+    UInt32 bufferOffset;
     UInt32 bufferSize;
     AudioStreamBasicDescription strdesc;
-    SDL_bool refill;
-    SDL_AudioStream *capturestream;
+    SDL_sem *ready_semaphore;
+    char *thread_error;
+    SDL_atomic_t shutdown;
 #if MACOSX_COREAUDIO
     AudioDeviceID deviceID;
 #else
diff -r 36ee99107390 -r dcb6c57df2fc src/audio/coreaudio/SDL_coreaudio.m
--- a/src/audio/coreaudio/SDL_coreaudio.m       Thu Mar 21 10:39:49 2019 -0400
+++ b/src/audio/coreaudio/SDL_coreaudio.m       Mon Mar 25 12:24:38 2019 -0400
@@ -26,7 +26,6 @@
 
 #include "SDL_audio.h"
 #include "SDL_hints.h"
-#include "SDL_timer.h"
 #include "../SDL_audio_c.h"
 #include "../SDL_sysaudio.h"
 #include "SDL_coreaudio.h"
@@ -410,27 +409,43 @@
 outputCallback(void *inUserData, AudioQueueRef inAQ, AudioQueueBufferRef inBuffer)
 {
     SDL_AudioDevice *this = (SDL_AudioDevice *) inUserData;
-    SDL_assert(inBuffer->mAudioDataBytesCapacity == this->hidden->bufferSize);
-    SDL_memcpy(inBuffer->mAudioData, this->hidden->buffer, this->hidden->bufferSize);
-    SDL_memset(this->hidden->buffer, '\0', this->hidden->bufferSize);  /* zero out in case we have to fill again without new data. */
-    inBuffer->mAudioDataByteSize = this->hidden->bufferSize;
+    if (SDL_AtomicGet(&this->hidden->shutdown)) {
+        return;  /* don't do anything. */
+    }
+
+    if (!SDL_AtomicGet(&this->enabled) || SDL_AtomicGet(&this->paused)) {
+        /* Supply silence if audio is not enabled or paused */
+        SDL_memset(inBuffer->mAudioData, this->spec.silence, inBuffer->mAudioDataBytesCapacity);
+    } else {
+        UInt32 remaining = inBuffer->mAudioDataBytesCapacity;
+        Uint8 *ptr = (Uint8 *) inBuffer->mAudioData;
+
+        while (remaining > 0) {
+            UInt32 len;
+            if (this->hidden->bufferOffset >= this->hidden->bufferSize) {
+                /* Generate the data */
+                SDL_LockMutex(this->mixer_lock);
+                (*this->callbackspec.callback)(this->callbackspec.userdata,
+                            this->hidden->buffer, this->hidden->bufferSize);
+                SDL_UnlockMutex(this->mixer_lock);
+                this->hidden->bufferOffset = 0;
+            }
+
+            len = this->hidden->bufferSize - this->hidden->bufferOffset;
+            if (len > remaining) {
+                len = remaining;
+            }
+            SDL_memcpy(ptr, (char *)this->hidden->buffer +
+                       this->hidden->bufferOffset, len);
+            ptr = ptr + len;
+            remaining -= len;
+            this->hidden->bufferOffset += len;
+        }
+    }
+
     AudioQueueEnqueueBuffer(this->hidden->audioQueue, inBuffer, 0, NULL);
-    this->hidden->refill = SDL_TRUE;
-}
 
-static Uint8 *
-COREAUDIO_GetDeviceBuf(_THIS)
-{
-    return this->hidden->buffer;
-}
-
-static void
-COREAUDIO_WaitDevice(_THIS)
-{
-    while (SDL_AtomicGet(&this->enabled) && !this->hidden->refill) {
-        CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0.10, 1);
-    }
-    this->hidden->refill = SDL_FALSE;
+    inBuffer->mAudioDataByteSize = inBuffer->mAudioDataBytesCapacity;
 }
 
 static void
@@ -439,46 +454,36 @@
               const AudioStreamPacketDescription *inPacketDescs )
 {
     SDL_AudioDevice *this = (SDL_AudioDevice *) inUserData;
-    if (SDL_AtomicGet(&this->enabled)) {
-        SDL_AudioStream *stream = this->hidden->capturestream;
-        if (SDL_AudioStreamPut(stream, inBuffer->mAudioData, inBuffer->mAudioDataByteSize) == -1) {
-            /* yikes, out of memory or something. I guess drop the buffer. Our WASAPI target kills the device in this case, though */
-        }
-        AudioQueueEnqueueBuffer(this->hidden->audioQueue, inBuffer, 0, NULL);
-        this->hidden->refill = SDL_TRUE;
-    }
-}
 
-static int
-COREAUDIO_CaptureFromDevice(_THIS, void *buffer, int buflen)
-{
-    SDL_AudioStream *stream = this->hidden->capturestream;
-    while (SDL_AtomicGet(&this->enabled)) {
-        const int avail = SDL_AudioStreamAvailable(stream);
-        if (avail > 0) {
-            const int cpy = SDL_min(buflen, avail);
-            SDL_AudioStreamGet(stream, buffer, cpy);
-            return cpy;
-        }
-
-        /* wait for more data, try again. */
-        while (SDL_AtomicGet(&this->enabled) && !this->hidden->refill) {
-            CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0.10, 1);
-        }
-        this->hidden->refill = SDL_FALSE;
+    if (SDL_AtomicGet(&this->shutdown)) {
+        return;  /* don't do anything. */
     }
 
-    return 0;  /* not enabled, giving up. */
-}
+    /* ignore unless we're active. */
+    if (!SDL_AtomicGet(&this->paused) && SDL_AtomicGet(&this->enabled) && !SDL_AtomicGet(&this->paused)) {
+        const Uint8 *ptr = (const Uint8 *) inBuffer->mAudioData;
+        UInt32 remaining = inBuffer->mAudioDataByteSize;
+        while (remaining > 0) {
+            UInt32 len = this->hidden->bufferSize - this->hidden->bufferOffset;
+            if (len > remaining) {
+                len = remaining;
+            }
 
-static void
-COREAUDIO_FlushCapture(_THIS)
-{
-    while (CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0, 1) == kCFRunLoopRunHandledSource) {
-        /* spin. */
+            SDL_memcpy((char *)this->hidden->buffer + this->hidden->bufferOffset, ptr, len);
+            ptr += len;
+            remaining -= len;
+            this->hidden->bufferOffset += len;
+
+            if (this->hidden->bufferOffset >= this->hidden->bufferSize) {
+                SDL_LockMutex(this->mixer_lock);
+                (*this->callbackspec.callback)(this->callbackspec.userdata, this->hidden->buffer, this->hidden->bufferSize);
+                SDL_UnlockMutex(this->mixer_lock);
+                this->hidden->bufferOffset = 0;
+            }
+        }
     }
-    this->hidden->refill = SDL_FALSE;
-    SDL_AudioStreamClear(this->hidden->capturestream);
+
+    AudioQueueEnqueueBuffer(this->hidden->audioQueue, inBuffer, 0, NULL);
 }
 
 
@@ -536,16 +541,25 @@
     update_audio_session(this, SDL_FALSE);
 #endif
 
+    /* if callback fires again, feed silence; don't call into the app. */
+    SDL_AtomicSet(&this->paused, 1);
+
     if (this->hidden->audioQueue) {
         AudioQueueDispose(this->hidden->audioQueue, 1);
     }
 
-    if (this->hidden->capturestream) {
-        SDL_FreeAudioStream(this->hidden->capturestream);
+    if (this->hidden->thread) {
+        SDL_AtomicSet(&this->hidden->shutdown, 1);
+        SDL_WaitThread(this->hidden->thread, NULL);
+    }
+
+    if (this->hidden->ready_semaphore) {
+        SDL_DestroySemaphore(this->hidden->ready_semaphore);
     }
 
     /* AudioQueueDispose() frees the actual buffer objects. */
     SDL_free(this->hidden->audioBuffer);
+    SDL_free(this->hidden->thread_error);
     SDL_free(this->hidden->buffer);
     SDL_free(this->hidden);
 
@@ -611,8 +625,6 @@
 }
 #endif
 
-
-/* this all happens in the audio thread, since it needs a separate runloop. */
 static int
 prepare_audioqueue(_THIS)
 {
@@ -652,6 +664,19 @@
 }
 #endif
 
+    /* Calculate the final parameters for this audio specification */
+    SDL_CalculateAudioSpec(&this->spec);
+
+    /* Allocate a sample buffer */
+    this->hidden->bufferSize = this->spec.size;
+    this->hidden->bufferOffset = iscapture ? 0 : this->hidden->bufferSize;
+
+    this->hidden->buffer = SDL_malloc(this->hidden->bufferSize);
+    if (this->hidden->buffer == NULL) {
+        SDL_OutOfMemory();
+        return 0;
+    }
+
     /* Make sure we can feed the device a minimum amount of time */
     double MINIMUM_AUDIO_BUFFER_TIME_MS = 15.0;
 #if defined(__IPHONEOS__)
@@ -666,7 +691,6 @@
         numAudioBuffers = ((int)SDL_ceil(MINIMUM_AUDIO_BUFFER_TIME_MS / msecs) * 2);
     }
 
-    this->hidden->numAudioBuffers = numAudioBuffers;
     this->hidden->audioBuffer = SDL_calloc(1, sizeof (AudioQueueBufferRef) * numAudioBuffers);
     if (this->hidden->audioBuffer == NULL) {
         SDL_OutOfMemory();
@@ -693,23 +717,29 @@
     return 1;
 }
 
-static void
-COREAUDIO_ThreadInit(_THIS)
+static int
+audioqueue_thread(void *arg)
 {
+    SDL_AudioDevice *this = (SDL_AudioDevice *) arg;
     const int rc = prepare_audioqueue(this);
     if (!rc) {
-        /* !!! FIXME: do this in RunAudio, and maybe block OpenDevice until ThreadInit finishes, too, to report an opening error */
-        SDL_OpenedAudioDeviceDisconnected(this);  /* oh well. */
+        this->hidden->thread_error = SDL_strdup(SDL_GetError());
+        SDL_SemPost(this->hidden->ready_semaphore);
+        return 0;
     }
-}
 
-static void
-COREAUDIO_PrepareToClose(_THIS)
-{
-    /* run long enough to queue some silence, so we know our actual audio
-       has been played */
-    CFRunLoopRunInMode(kCFRunLoopDefaultMode, (((this->spec.samples * 1000) / this->spec.freq) * 2) / 1000.0f, 0);
-    AudioQueueStop(this->hidden->audioQueue, 1);
+    /* init was successful, alert parent thread and start running... */
+    SDL_SemPost(this->hidden->ready_semaphore);
+    while (!SDL_AtomicGet(&this->hidden->shutdown)) {
+        CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0.10, 1);
+    }
+
+    if (!this->iscapture) {  /* Drain off any pending playback. */
+        const CFTimeInterval secs = (((this->spec.size / (SDL_AUDIO_BITSIZE(this->spec.format) / 8)) / this->spec.channels) / ((CFTimeInterval) this->spec.freq)) * 2.0;
+        CFRunLoopRunInMode(kCFRunLoopDefaultMode, secs, 0);
+    }
+
+    return 0;
 }
 
 static int
@@ -796,23 +826,28 @@
     }
 #endif
 
-    /* Calculate the final parameters for this audio specification */
-    SDL_CalculateAudioSpec(&this->spec);
-
-    if (iscapture) {
-        this->hidden->capturestream = SDL_NewAudioStream(this->spec.format, this->spec.channels, this->spec.freq, this->spec.format, this->spec.channels, this->spec.freq);
-        if (!this->hidden->capturestream) {
-            return -1;  /* already set SDL_Error */
-        }
-    } else {
-        this->hidden->bufferSize = this->spec.size;
-        this->hidden->buffer = SDL_malloc(this->hidden->bufferSize);
-        if (this->hidden->buffer == NULL) {
-            return SDL_OutOfMemory();
-        }
+    /* This has to init in a new thread so it can get its own CFRunLoop. :/ */
+    SDL_AtomicSet(&this->hidden->shutdown, 0);
+    this->hidden->ready_semaphore = SDL_CreateSemaphore(0);
+    if (!this->hidden->ready_semaphore) {
+        return -1;  /* oh well. */
     }
 
-    return 0;
+    this->hidden->thread = SDL_CreateThreadInternal(audioqueue_thread, "AudioQueue thread", 512 * 1024, this);
+    if (!this->hidden->thread) {
+        return -1;
+    }
+
+    SDL_SemWait(this->hidden->ready_semaphore);
+    SDL_DestroySemaphore(this->hidden->ready_semaphore);
+    this->hidden->ready_semaphore = NULL;
+
+    if ((this->hidden->thread != NULL) && (this->hidden->thread_error != NULL)) {
+        SDL_SetError("%s", this->hidden->thread_error);
+        return -1;
+    }
+
+    return (this->hidden->thread != NULL) ? 0 : -1;
 }
 
 static void
@@ -832,12 +867,6 @@
     impl->OpenDevice = COREAUDIO_OpenDevice;
     impl->CloseDevice = COREAUDIO_CloseDevice;
     impl->Deinitialize = COREAUDIO_Deinitialize;
-    impl->ThreadInit = COREAUDIO_ThreadInit;
-    impl->WaitDevice = COREAUDIO_WaitDevice;
-    impl->GetDeviceBuf = COREAUDIO_GetDeviceBuf;
-    impl->PrepareToClose = COREAUDIO_PrepareToClose;
-    impl->CaptureFromDevice = COREAUDIO_CaptureFromDevice;
-    impl->FlushCapture = COREAUDIO_FlushCapture;
 
 #if MACOSX_COREAUDIO
     impl->DetectDevices = COREAUDIO_DetectDevices;
@@ -847,6 +876,7 @@
     impl->OnlyHasDefaultCaptureDevice = 1;
 #endif
 
+    impl->ProvidesOwnCallbackThread = 1;
     impl->HasCaptureSupport = 1;
 
     return 1;   /* this audio target is available. */