SoundIoOutStream, SoundIoInStream: void * -> union

For better cache locality and lower mlock requirements.

README.md

@@ -280,8 +280,6 @@ view `coverage/index.html` in a browser.
  0. Support PulseAudio proplist properties for main context and streams
  0. custom allocator support
  0. mlock memory which is accessed in the real time path
- 0. instead of `void *backend_data` use a union for better cache locality
-    and smaller mlock requirements
  0. Consider testing on FreeBSD
  0. make rtprio warning a callback and have existing behavior be the default callback
  0. write detailed docs on buffer underflows explaining when they occur, what state

src/alsa.cpp

@@ -8,7 +8,6 @@
 #include "alsa.hpp"
 #include "soundio.hpp"
 
-#include <alsa/asoundlib.h>
 #include <sys/inotify.h>
 #include <math.h>
 
@@ -23,39 +22,6 @@ static snd_pcm_access_t prioritized_access_types[] = {
 };
 
 
-struct SoundIoOutStreamAlsa {
-    snd_pcm_t *handle;
-    snd_pcm_chmap_t *chmap;
-    int chmap_size;
-    snd_pcm_uframes_t offset;
-    snd_pcm_access_t access;
-    int sample_buffer_size;
-    char *sample_buffer;
-    int poll_fd_count;
-    struct pollfd *poll_fds;
-    SoundIoOsThread *thread;
-    atomic_flag thread_exit_flag;
-    int period_size;
-    SoundIoChannelArea areas[SOUNDIO_MAX_CHANNELS];
-};
-
-struct SoundIoInStreamAlsa {
-    snd_pcm_t *handle;
-    snd_pcm_chmap_t *chmap;
-    int chmap_size;
-    snd_pcm_uframes_t offset;
-    snd_pcm_access_t access;
-    int sample_buffer_size;
-    char *sample_buffer;
-    int poll_fd_count;
-    struct pollfd *poll_fds;
-    SoundIoOsThread *thread;
-    atomic_flag thread_exit_flag;
-    int period_size;
-    int read_frame_count;
-    SoundIoChannelArea areas[SOUNDIO_MAX_CHANNELS];
-};
-
 static void wakeup_device_poll(SoundIoAlsa *sia) {
     ssize_t amt = write(sia->notify_pipe_fd[1], "a", 1);
     if (amt == -1) {
@@ -881,9 +847,7 @@ static void wakeup(SoundIoPrivate *si) {
 }
 
 static void outstream_destroy_alsa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os) {
-    SoundIoOutStreamAlsa *osa = (SoundIoOutStreamAlsa *) os->backend_data;
+    SoundIoOutStreamAlsa *osa = &os->backend_data.alsa;
-    if (!osa)
-        return;
 
     if (osa->thread) {
         osa->thread_exit_flag.clear();
@@ -898,14 +862,11 @@ static void outstream_destroy_alsa(SoundIoPrivate *si, SoundIoOutStreamPrivate *
     deallocate(osa->chmap, osa->chmap_size);
 
     deallocate(osa->sample_buffer, osa->sample_buffer_size);
-
-    destroy(osa);
-    os->backend_data = nullptr;
 }
 
 static int xrun_recovery(SoundIoOutStreamPrivate *os, int err) {
     SoundIoOutStream *outstream = &os->pub;
-    SoundIoOutStreamAlsa *osa = (SoundIoOutStreamAlsa *)os->backend_data;
+    SoundIoOutStreamAlsa *osa = &os->backend_data.alsa;
     if (err == -EPIPE) {
         err = snd_pcm_prepare(osa->handle);
         if (err >= 0)
@@ -924,7 +885,7 @@ static int xrun_recovery(SoundIoOutStreamPrivate *os, int err) {
 }
 
 static int instream_xrun_recovery(SoundIoInStreamPrivate *is, int err) {
-    SoundIoInStreamAlsa *isa = (SoundIoInStreamAlsa *)is->backend_data;
+    SoundIoInStreamAlsa *isa = &is->backend_data.alsa;
     if (err == -EPIPE) {
         err = snd_pcm_prepare(isa->handle);
     } else if (err == -ESTRPIPE) {
@@ -977,7 +938,7 @@ static int instream_wait_for_poll(SoundIoInStreamAlsa *isa) {
 void outstream_thread_run(void *arg) {
     SoundIoOutStreamPrivate *os = (SoundIoOutStreamPrivate *) arg;
     SoundIoOutStream *outstream = &os->pub;
-    SoundIoOutStreamAlsa *osa = (SoundIoOutStreamAlsa *) os->backend_data;
+    SoundIoOutStreamAlsa *osa = &os->backend_data.alsa;
 
     int err;
 
@@ -1046,37 +1007,37 @@ void outstream_thread_run(void *arg) {
 static void instream_thread_run(void *arg) {
     SoundIoInStreamPrivate *is = (SoundIoInStreamPrivate *) arg;
     SoundIoInStream *instream = &is->pub;
-    SoundIoInStreamAlsa *osa = (SoundIoInStreamAlsa *) is->backend_data;
+    SoundIoInStreamAlsa *isa = &is->backend_data.alsa;
 
     int err;
 
     for (;;) {
-        snd_pcm_state_t state = snd_pcm_state(osa->handle);
+        snd_pcm_state_t state = snd_pcm_state(isa->handle);
         switch (state) {
             case SND_PCM_STATE_SETUP:
-                if ((err = snd_pcm_prepare(osa->handle)) < 0) {
+                if ((err = snd_pcm_prepare(isa->handle)) < 0) {
                     instream->error_callback(instream, SoundIoErrorStreaming);
                     return;
                 }
                 continue;
             case SND_PCM_STATE_PREPARED:
-                if ((err = snd_pcm_start(osa->handle)) < 0) {
+                if ((err = snd_pcm_start(isa->handle)) < 0) {
                     instream->error_callback(instream, SoundIoErrorStreaming);
                     return;
                 }
                 continue;
             case SND_PCM_STATE_RUNNING:
             {
-                if ((err = instream_wait_for_poll(osa)) < 0) {
+                if ((err = instream_wait_for_poll(isa)) < 0) {
-                    if (!osa->thread_exit_flag.test_and_set())
+                    if (!isa->thread_exit_flag.test_and_set())
                         return;
                     instream->error_callback(instream, SoundIoErrorStreaming);
                     return;
                 }
-                if (!osa->thread_exit_flag.test_and_set())
+                if (!isa->thread_exit_flag.test_and_set())
                     return;
 
-                snd_pcm_sframes_t avail = snd_pcm_avail_update(osa->handle);
+                snd_pcm_sframes_t avail = snd_pcm_avail_update(isa->handle);
                 if (avail < 0) {
                     if ((err = instream_xrun_recovery(is, avail)) < 0) {
                         instream->error_callback(instream, SoundIoErrorStreaming);
@@ -1111,6 +1072,7 @@ static void instream_thread_run(void *arg) {
 }
 
 static int outstream_open_alsa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os) {
+    SoundIoOutStreamAlsa *osa = &os->backend_data.alsa;
     SoundIoOutStream *outstream = &os->pub;
     SoundIoDevice *device = outstream->device;
 
@@ -1123,13 +1085,6 @@ static int outstream_open_alsa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os)
     if (outstream->prebuf_duration == -1.0)
         outstream->prebuf_duration = outstream->buffer_duration;
 
-    SoundIoOutStreamAlsa *osa = create<SoundIoOutStreamAlsa>();
-    if (!osa) {
-        outstream_destroy_alsa(si, os);
-        return SoundIoErrorNoMem;
-    }
-    os->backend_data = osa;
-
     int ch_count = outstream->layout.channel_count;
 
     osa->chmap_size = sizeof(int) + sizeof(int) * ch_count;
@@ -1284,7 +1239,7 @@ static int outstream_open_alsa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os)
 }
 
 static int outstream_start_alsa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os) {
-    SoundIoOutStreamAlsa *osa = (SoundIoOutStreamAlsa *) os->backend_data;
+    SoundIoOutStreamAlsa *osa = &os->backend_data.alsa;
 
     assert(!osa->thread);
 
@@ -1302,7 +1257,7 @@ int outstream_begin_write_alsa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os,
         struct SoundIoChannelArea **out_areas, int *frame_count)
 {
     *out_areas = nullptr;
-    SoundIoOutStreamAlsa *osa = (SoundIoOutStreamAlsa *) os->backend_data;
+    SoundIoOutStreamAlsa *osa = &os->backend_data.alsa;
     SoundIoOutStream *outstream = &os->pub;
 
     if (osa->access == SND_PCM_ACCESS_RW_INTERLEAVED) {
@@ -1345,7 +1300,7 @@ int outstream_begin_write_alsa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os,
 }
 
 static int outstream_end_write_alsa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os, int frame_count) {
-    SoundIoOutStreamAlsa *osa = (SoundIoOutStreamAlsa *) os->backend_data;
+    SoundIoOutStreamAlsa *osa = &os->backend_data.alsa;
     SoundIoOutStream *outstream = &os->pub;
 
     snd_pcm_sframes_t commitres;
@@ -1373,7 +1328,7 @@ static int outstream_end_write_alsa(SoundIoPrivate *si, SoundIoOutStreamPrivate
 static int outstream_clear_buffer_alsa(SoundIoPrivate *si,
         SoundIoOutStreamPrivate *os)
 {
-    SoundIoOutStreamAlsa *osa = (SoundIoOutStreamAlsa *) os->backend_data;
+    SoundIoOutStreamAlsa *osa = &os->backend_data.alsa;
     int err;
     if ((err = snd_pcm_reset(osa->handle)) < 0)
         return SoundIoErrorStreaming;
@@ -1381,7 +1336,7 @@ static int outstream_clear_buffer_alsa(SoundIoPrivate *si,
 }
 
 static int outstream_pause_alsa(struct SoundIoPrivate *si, struct SoundIoOutStreamPrivate *os, bool pause) {
-    SoundIoOutStreamAlsa *osa = (SoundIoOutStreamAlsa *) os->backend_data;
+    SoundIoOutStreamAlsa *osa = &os->backend_data.alsa;
     int err;
     if ((err = snd_pcm_pause(osa->handle, pause)) < 0)
         return SoundIoErrorIncompatibleDevice;
@@ -1389,9 +1344,7 @@ static int outstream_pause_alsa(struct SoundIoPrivate *si, struct SoundIoOutStre
 }
 
 static void instream_destroy_alsa(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
-    SoundIoInStreamAlsa *isa = (SoundIoInStreamAlsa *) is->backend_data;
+    SoundIoInStreamAlsa *isa = &is->backend_data.alsa;
-    if (!isa)
-        return;
 
     if (isa->thread) {
         isa->thread_exit_flag.clear();
@@ -1404,12 +1357,10 @@ static void instream_destroy_alsa(SoundIoPrivate *si, SoundIoInStreamPrivate *is
     deallocate(isa->poll_fds, isa->poll_fd_count);
     deallocate(isa->chmap, isa->chmap_size);
     deallocate(isa->sample_buffer, isa->sample_buffer_size);
-
-    destroy(isa);
-    is->backend_data = nullptr;
 }
 
 static int instream_open_alsa(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
+    SoundIoInStreamAlsa *isa = &is->backend_data.alsa;
     SoundIoInStream *instream = &is->pub;
     SoundIoDevice *device = instream->device;
 
@@ -1420,13 +1371,6 @@ static int instream_open_alsa(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
                 instream->buffer_duration / 8.0, device->period_duration_max);
     }
 
-    SoundIoInStreamAlsa *isa = create<SoundIoInStreamAlsa>();
-    if (!isa) {
-        instream_destroy_alsa(si, is);
-        return SoundIoErrorNoMem;
-    }
-    is->backend_data = isa;
-
     int ch_count = instream->layout.channel_count;
 
     isa->chmap_size = sizeof(int) + sizeof(int) * ch_count;
@@ -1568,7 +1512,7 @@ static int instream_open_alsa(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
 }
 
 static int instream_start_alsa(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
-    SoundIoInStreamAlsa *isa = (SoundIoInStreamAlsa *) is->backend_data;
+    SoundIoInStreamAlsa *isa = &is->backend_data.alsa;
 
     assert(!isa->thread);
 
@@ -1586,7 +1530,7 @@ static int instream_begin_read_alsa(SoundIoPrivate *si,
         SoundIoInStreamPrivate *is, SoundIoChannelArea **out_areas, int *frame_count)
 {
     *out_areas = nullptr;
-    SoundIoInStreamAlsa *isa = (SoundIoInStreamAlsa *) is->backend_data;
+    SoundIoInStreamAlsa *isa = &is->backend_data.alsa;
     SoundIoInStream *instream = &is->pub;
 
     if (isa->access == SND_PCM_ACCESS_RW_INTERLEAVED) {
@@ -1646,7 +1590,7 @@ static int instream_begin_read_alsa(SoundIoPrivate *si,
 }
 
 static int instream_end_read_alsa(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
-    SoundIoInStreamAlsa *isa = (SoundIoInStreamAlsa *) is->backend_data;
+    SoundIoInStreamAlsa *isa = &is->backend_data.alsa;
 
     if (isa->access == SND_PCM_ACCESS_RW_INTERLEAVED) {
         return 0;
@@ -1665,7 +1609,7 @@ static int instream_end_read_alsa(SoundIoPrivate *si, SoundIoInStreamPrivate *is
 }
 
 static int instream_pause_alsa(struct SoundIoPrivate *si, struct SoundIoInStreamPrivate *is, bool pause) {
-    SoundIoInStreamAlsa *isa = (SoundIoInStreamAlsa *) is->backend_data;
+    SoundIoInStreamAlsa *isa = &is->backend_data.alsa;
     int err;
     if ((err = snd_pcm_pause(isa->handle, pause)) < 0)
         return SoundIoErrorIncompatibleDevice;

src/alsa.hpp

@@ -8,9 +8,12 @@
 #ifndef SOUNDIO_ALSA_HPP
 #define SOUNDIO_ALSA_HPP
 
+#include "soundio.h"
 #include "os.hpp"
 #include "atomics.hpp"
 
+#include <alsa/asoundlib.h>
+
 int soundio_alsa_init(struct SoundIoPrivate *si);
 
 struct SoundIoDeviceAlsa {
@@ -32,4 +35,37 @@ struct SoundIoAlsa {
     struct SoundIoDevicesInfo *ready_devices_info;
 };
 
+struct SoundIoOutStreamAlsa {
+    snd_pcm_t *handle;
+    snd_pcm_chmap_t *chmap;
+    int chmap_size;
+    snd_pcm_uframes_t offset;
+    snd_pcm_access_t access;
+    int sample_buffer_size;
+    char *sample_buffer;
+    int poll_fd_count;
+    struct pollfd *poll_fds;
+    SoundIoOsThread *thread;
+    atomic_flag thread_exit_flag;
+    int period_size;
+    SoundIoChannelArea areas[SOUNDIO_MAX_CHANNELS];
+};
+
+struct SoundIoInStreamAlsa {
+    snd_pcm_t *handle;
+    snd_pcm_chmap_t *chmap;
+    int chmap_size;
+    snd_pcm_uframes_t offset;
+    snd_pcm_access_t access;
+    int sample_buffer_size;
+    char *sample_buffer;
+    int poll_fd_count;
+    struct pollfd *poll_fds;
+    SoundIoOsThread *thread;
+    atomic_flag thread_exit_flag;
+    int period_size;
+    int read_frame_count;
+    SoundIoChannelArea areas[SOUNDIO_MAX_CHANNELS];
+};
+
 #endif

src/dummy.cpp

@@ -7,41 +7,15 @@
 
 #include "dummy.hpp"
 #include "soundio.hpp"
-#include "atomics.hpp"
-#include "ring_buffer.hpp"
 
 #include <stdio.h>
 #include <string.h>
 #include <math.h>
 
-struct SoundIoOutStreamDummy {
-    struct SoundIoOsThread *thread;
-    struct SoundIoOsCond *cond;
-    atomic_flag abort_flag;
-    int buffer_frame_count;
-    struct SoundIoRingBuffer ring_buffer;
-    int prebuf_frame_count;
-    int prebuf_frames_left;
-    long frames_consumed;
-    double playback_start_time;
-    SoundIoChannelArea areas[SOUNDIO_MAX_CHANNELS];
-};
-
-struct SoundIoInStreamDummy {
-    struct SoundIoOsThread *thread;
-    struct SoundIoOsCond *cond;
-    atomic_flag abort_flag;
-    int read_frame_count;
-    int buffer_frame_count;
-    struct SoundIoRingBuffer ring_buffer;
-    int hole_size;
-    SoundIoChannelArea areas[SOUNDIO_MAX_CHANNELS];
-};
-
 static void playback_thread_run(void *arg) {
     SoundIoOutStreamPrivate *os = (SoundIoOutStreamPrivate *)arg;
     SoundIoOutStream *outstream = &os->pub;
-    SoundIoOutStreamDummy *osd = (SoundIoOutStreamDummy *)os->backend_data;
+    SoundIoOutStreamDummy *osd = &os->backend_data.dummy;
 
     double start_time = soundio_os_get_time();
     osd->playback_start_time = start_time;
@@ -90,7 +64,7 @@ static void playback_thread_run(void *arg) {
 static void capture_thread_run(void *arg) {
     SoundIoInStreamPrivate *is = (SoundIoInStreamPrivate *)arg;
     SoundIoInStream *instream = &is->pub;
-    SoundIoInStreamDummy *isd = (SoundIoInStreamDummy *)is->backend_data;
+    SoundIoInStreamDummy *isd = &is->backend_data.dummy;
 
     long frames_consumed = 0;
     double start_time = soundio_os_get_time();
@@ -150,9 +124,7 @@ static void wakeup(SoundIoPrivate *si) {
 }
 
 static void outstream_destroy_dummy(SoundIoPrivate *si, SoundIoOutStreamPrivate *os) {
-    SoundIoOutStreamDummy *osd = (SoundIoOutStreamDummy *)os->backend_data;
+    SoundIoOutStreamDummy *osd = &os->backend_data.dummy;
-    if (!osd)
-        return;
 
     if (osd->thread) {
         osd->abort_flag.clear();
@@ -164,12 +136,10 @@ static void outstream_destroy_dummy(SoundIoPrivate *si, SoundIoOutStreamPrivate
     osd->cond = nullptr;
 
     soundio_ring_buffer_deinit(&osd->ring_buffer);
-
-    destroy(osd);
-    os->backend_data = nullptr;
 }
 
 static int outstream_open_dummy(SoundIoPrivate *si, SoundIoOutStreamPrivate *os) {
+    SoundIoOutStreamDummy *osd = &os->backend_data.dummy;
     SoundIoOutStream *outstream = &os->pub;
     SoundIoDevice *device = outstream->device;
 
@@ -180,13 +150,6 @@ static int outstream_open_dummy(SoundIoPrivate *si, SoundIoOutStreamPrivate *os)
                 outstream->buffer_duration / 2.0, device->period_duration_max);
     }
 
-    SoundIoOutStreamDummy *osd = create<SoundIoOutStreamDummy>();
-    if (!osd) {
-        outstream_destroy_dummy(si, os);
-        return SoundIoErrorNoMem;
-    }
-    os->backend_data = osd;
-
     int err;
     int buffer_size = outstream->bytes_per_frame * outstream->sample_rate * outstream->buffer_duration;
     if ((err = soundio_ring_buffer_init(&osd->ring_buffer, buffer_size))) {
@@ -212,7 +175,7 @@ static int outstream_open_dummy(SoundIoPrivate *si, SoundIoOutStreamPrivate *os)
 }
 
 static int outstream_pause_dummy(struct SoundIoPrivate *si, struct SoundIoOutStreamPrivate *os, bool pause) {
-    SoundIoOutStreamDummy *osd = (SoundIoOutStreamDummy *)os->backend_data;
+    SoundIoOutStreamDummy *osd = &os->backend_data.dummy;
     if (pause) {
         if (osd->thread) {
             osd->abort_flag.clear();
@@ -242,7 +205,7 @@ static int outstream_begin_write_dummy(SoundIoPrivate *si,
     *out_areas = nullptr;
 
     SoundIoOutStream *outstream = &os->pub;
-    SoundIoOutStreamDummy *osd = (SoundIoOutStreamDummy *)os->backend_data;
+    SoundIoOutStreamDummy *osd = &os->backend_data.dummy;
 
     assert(*frame_count >= 0);
     assert(*frame_count <= osd->buffer_frame_count);
@@ -264,7 +227,7 @@ static int outstream_begin_write_dummy(SoundIoPrivate *si,
 }
 
 static int outstream_end_write_dummy(SoundIoPrivate *si, SoundIoOutStreamPrivate *os, int frame_count) {
-    SoundIoOutStreamDummy *osd = (SoundIoOutStreamDummy *)os->backend_data;
+    SoundIoOutStreamDummy *osd = &os->backend_data.dummy;
     SoundIoOutStream *outstream = &os->pub;
     int byte_count = frame_count * outstream->bytes_per_frame;
     soundio_ring_buffer_advance_write_ptr(&osd->ring_buffer, byte_count);
@@ -279,16 +242,14 @@ static int outstream_end_write_dummy(SoundIoPrivate *si, SoundIoOutStreamPrivate
 }
 
 static int outstream_clear_buffer_dummy(SoundIoPrivate *si, SoundIoOutStreamPrivate *os) {
-    SoundIoOutStreamDummy *osd = (SoundIoOutStreamDummy *)os->backend_data;
+    SoundIoOutStreamDummy *osd = &os->backend_data.dummy;
     soundio_ring_buffer_clear(&osd->ring_buffer);
     osd->prebuf_frames_left = osd->prebuf_frame_count;
     return 0;
 }
 
 static void instream_destroy_dummy(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
-    SoundIoInStreamDummy *isd = (SoundIoInStreamDummy *)is->backend_data;
+    SoundIoInStreamDummy *isd = &is->backend_data.dummy;
-    if (!isd)
-        return;
 
     if (isd->thread) {
         isd->abort_flag.clear();
@@ -300,12 +261,10 @@ static void instream_destroy_dummy(SoundIoPrivate *si, SoundIoInStreamPrivate *i
     isd->cond = nullptr;
 
     soundio_ring_buffer_deinit(&isd->ring_buffer);
-
-    destroy(isd);
-    is->backend_data = nullptr;
 }
 
 static int instream_open_dummy(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
+    SoundIoInStreamDummy *isd = &is->backend_data.dummy;
     SoundIoInStream *instream = &is->pub;
     SoundIoDevice *device = instream->device;
 
@@ -316,13 +275,6 @@ static int instream_open_dummy(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
                 instream->buffer_duration / 8.0, instream->device->period_duration_max);
     }
 
-    SoundIoInStreamDummy *isd = create<SoundIoInStreamDummy>();
-    if (!isd) {
-        instream_destroy_dummy(si, is);
-        return SoundIoErrorNoMem;
-    }
-    is->backend_data = isd;
-
     int err;
     int buffer_size = instream->bytes_per_frame * instream->sample_rate * instream->buffer_duration;
     if ((err = soundio_ring_buffer_init(&isd->ring_buffer, buffer_size))) {
@@ -344,7 +296,7 @@ static int instream_open_dummy(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
 }
 
 static int instream_pause_dummy(SoundIoPrivate *si, SoundIoInStreamPrivate *is, bool pause) {
-    SoundIoInStreamDummy *isd = (SoundIoInStreamDummy *)is->backend_data;
+    SoundIoInStreamDummy *isd = &is->backend_data.dummy;
     if (pause) {
         if (isd->thread) {
             isd->abort_flag.clear();
@@ -372,7 +324,7 @@ static int instream_begin_read_dummy(SoundIoPrivate *si,
         SoundIoInStreamPrivate *is, SoundIoChannelArea **out_areas, int *frame_count)
 {
     SoundIoInStream *instream = &is->pub;
-    SoundIoInStreamDummy *isd = (SoundIoInStreamDummy *)is->backend_data;
+    SoundIoInStreamDummy *isd = &is->backend_data.dummy;
 
     assert(*frame_count >= 0);
     assert(*frame_count <= isd->buffer_frame_count);
@@ -403,7 +355,7 @@ static int instream_begin_read_dummy(SoundIoPrivate *si,
 }
 
 static int instream_end_read_dummy(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
-    SoundIoInStreamDummy *isd = (SoundIoInStreamDummy *)is->backend_data;
+    SoundIoInStreamDummy *isd = &is->backend_data.dummy;
     SoundIoInStream *instream = &is->pub;
 
     if (isd->hole_size > 0) {

src/dummy.hpp

@@ -8,7 +8,10 @@
 #ifndef SOUNDIO_DUMMY_HPP
 #define SOUNDIO_DUMMY_HPP
 
+#include "soundio.h"
 #include "os.hpp"
+#include "atomics.hpp"
+#include "ring_buffer.hpp"
 
 int soundio_dummy_init(struct SoundIoPrivate *si);
 
@@ -22,4 +25,28 @@ struct SoundIoDeviceDummy {
 
 };
 
+struct SoundIoOutStreamDummy {
+    struct SoundIoOsThread *thread;
+    struct SoundIoOsCond *cond;
+    atomic_flag abort_flag;
+    int buffer_frame_count;
+    struct SoundIoRingBuffer ring_buffer;
+    int prebuf_frame_count;
+    int prebuf_frames_left;
+    long frames_consumed;
+    double playback_start_time;
+    SoundIoChannelArea areas[SOUNDIO_MAX_CHANNELS];
+};
+
+struct SoundIoInStreamDummy {
+    struct SoundIoOsThread *thread;
+    struct SoundIoOsCond *cond;
+    atomic_flag abort_flag;
+    int read_frame_count;
+    int buffer_frame_count;
+    struct SoundIoRingBuffer ring_buffer;
+    int hole_size;
+    SoundIoChannelArea areas[SOUNDIO_MAX_CHANNELS];
+};
+
 #endif

src/jack.cpp

@@ -14,11 +14,6 @@
 
 static atomic_flag global_msg_callback_flag = ATOMIC_FLAG_INIT;
 
-struct SoundIoOutStreamJack {
-    jack_client_t *client;
-    jack_port_t *ports[SOUNDIO_MAX_CHANNELS];
-};
-
 struct SoundIoJackPort {
     const char *name;
     int name_len;
@@ -80,17 +75,13 @@ static int outstream_process_callback(jack_nframes_t nframes, void *arg) {
 }
 
 static void outstream_destroy_jack(struct SoundIoPrivate *is, struct SoundIoOutStreamPrivate *os) {
-    SoundIoOutStreamJack *osj = (SoundIoOutStreamJack *) os->backend_data;
+    SoundIoOutStreamJack *osj = &os->backend_data.jack;
-    if (!osj)
-        return;
 
     jack_client_close(osj->client);
-
-    destroy(osj);
-    os->backend_data = nullptr;
 }
 
 static int outstream_open_jack(struct SoundIoPrivate *si, struct SoundIoOutStreamPrivate *os) {
+    SoundIoOutStreamJack *osj = &os->backend_data.jack;
     SoundIoOutStream *outstream = &os->pub;
     //TODO SoundIoDevice *device = outstream->device;
 
@@ -98,13 +89,6 @@ static int outstream_open_jack(struct SoundIoPrivate *si, struct SoundIoOutStrea
     outstream->period_duration = 0.0; // TODO
     outstream->prebuf_duration = 0.0; // TODO
 
-    SoundIoOutStreamJack *osj = create<SoundIoOutStreamJack>();
-    if (!osj) {
-        outstream_destroy_jack(si, os);
-        return SoundIoErrorNoMem;
-    }
-    os->backend_data = osj;
-
     outstream->layout_error = SoundIoErrorIncompatibleBackend;
 
     jack_status_t status;
@@ -145,7 +129,7 @@ static int outstream_open_jack(struct SoundIoPrivate *si, struct SoundIoOutStrea
 }
 
 static int outstream_pause_jack(struct SoundIoPrivate *si, struct SoundIoOutStreamPrivate *os, bool pause) {
-    SoundIoOutStreamJack *osj = (SoundIoOutStreamJack *) os->backend_data;
+    SoundIoOutStreamJack *osj = &os->backend_data.jack;
     SoundIoOutStream *outstream = &os->pub;
     int err;
     if (pause) {

src/jack.hpp

@@ -8,6 +8,7 @@
 #ifndef SOUNDIO_JACK_HPP
 #define SOUNDIO_JACK_HPP
 
+#include "soundio.h"
 #include "os.hpp"
 
 #include <jack/jack.h>
@@ -29,5 +30,13 @@ struct SoundIoJack {
     int buffer_size;
 };
 
-#endif
+struct SoundIoOutStreamJack {
+    jack_client_t *client;
+    jack_port_t *ports[SOUNDIO_MAX_CHANNELS];
+};
 
+struct SoundIoInStreamJack {
+
+};
+
+#endif

src/pulseaudio.cpp

@@ -13,21 +13,6 @@
 #include <stdio.h>
 
 
-struct SoundIoOutStreamPulseAudio {
-    pa_stream *stream;
-    atomic_bool stream_ready;
-    pa_buffer_attr buffer_attr;
-    char *write_ptr;
-    SoundIoChannelArea areas[SOUNDIO_MAX_CHANNELS];
-};
-
-struct SoundIoInStreamPulseAudio {
-    pa_stream *stream;
-    atomic_bool stream_ready;
-    pa_buffer_attr buffer_attr;
-    SoundIoChannelArea areas[SOUNDIO_MAX_CHANNELS];
-};
-
 static void subscribe_callback(pa_context *context,
         pa_subscription_event_type_t event_bits, uint32_t index, void *userdata)
 {
@@ -570,7 +555,7 @@ static void playback_stream_state_callback(pa_stream *stream, void *userdata) {
     SoundIo *soundio = outstream->device->soundio;
     SoundIoPrivate *si = (SoundIoPrivate *)soundio;
     SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
-    SoundIoOutStreamPulseAudio *ospa = (SoundIoOutStreamPulseAudio *)os->backend_data;
+    SoundIoOutStreamPulseAudio *ospa = &os->backend_data.pulseaudio;
     switch (pa_stream_get_state(stream)) {
         case PA_STREAM_UNCONNECTED:
         case PA_STREAM_CREATING:
@@ -598,9 +583,7 @@ static void playback_stream_write_callback(pa_stream *stream, size_t nbytes, voi
 }
 
 static void outstream_destroy_pa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os) {
-    SoundIoOutStreamPulseAudio *ospa = (SoundIoOutStreamPulseAudio *)os->backend_data;
+    SoundIoOutStreamPulseAudio *ospa = &os->backend_data.pulseaudio;
-    if (!ospa)
-        return;
 
     SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     pa_stream *stream = ospa->stream;
@@ -618,21 +601,12 @@ static void outstream_destroy_pa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os
 
         ospa->stream = nullptr;
     }
-
-    destroy(ospa);
-    os->backend_data = nullptr;
 }
 
 static int outstream_open_pa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os) {
+    SoundIoOutStreamPulseAudio *ospa = &os->backend_data.pulseaudio;
     SoundIoOutStream *outstream = &os->pub;
 
-    SoundIoOutStreamPulseAudio *ospa = create<SoundIoOutStreamPulseAudio>();
-    if (!ospa) {
-        outstream_destroy_pa(si, os);
-        return SoundIoErrorNoMem;
-    }
-    os->backend_data = ospa;
-
     SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     ospa->stream_ready = false;
 
@@ -686,7 +660,7 @@ static int outstream_open_pa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os) {
 static int outstream_start_pa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os) {
     SoundIoOutStream *outstream = &os->pub;
     SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
-    SoundIoOutStreamPulseAudio *ospa = (SoundIoOutStreamPulseAudio *)os->backend_data;
+    SoundIoOutStreamPulseAudio *ospa = &os->backend_data.pulseaudio;
 
     pa_threaded_mainloop_lock(sipa->main_loop);
 
@@ -720,7 +694,7 @@ static int outstream_begin_write_pa(SoundIoPrivate *si,
     *out_areas = nullptr;
 
     SoundIoOutStream *outstream = &os->pub;
-    SoundIoOutStreamPulseAudio *ospa = (SoundIoOutStreamPulseAudio *)os->backend_data;
+    SoundIoOutStreamPulseAudio *ospa = &os->backend_data.pulseaudio;
     pa_stream *stream = ospa->stream;
     size_t byte_count = *frame_count * outstream->bytes_per_frame;
     if (pa_stream_begin_write(stream, (void**)&ospa->write_ptr, &byte_count))
@@ -739,7 +713,7 @@ static int outstream_begin_write_pa(SoundIoPrivate *si,
 
 static int outstream_end_write_pa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os, int frame_count) {
     SoundIoOutStream *outstream = &os->pub;
-    SoundIoOutStreamPulseAudio *ospa = (SoundIoOutStreamPulseAudio *)os->backend_data;
+    SoundIoOutStreamPulseAudio *ospa = &os->backend_data.pulseaudio;
     pa_stream *stream = ospa->stream;
     assert(frame_count > 0);
     size_t byte_count = frame_count * outstream->bytes_per_frame;
@@ -752,7 +726,7 @@ static int outstream_end_write_pa(SoundIoPrivate *si, SoundIoOutStreamPrivate *o
 static int outstream_clear_buffer_pa(SoundIoPrivate *si,
         SoundIoOutStreamPrivate *os)
 {
-    SoundIoOutStreamPulseAudio *ospa = (SoundIoOutStreamPulseAudio *)os->backend_data;
+    SoundIoOutStreamPulseAudio *ospa = &os->backend_data.pulseaudio;
     SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     pa_stream *stream = ospa->stream;
     pa_threaded_mainloop_lock(sipa->main_loop);
@@ -765,7 +739,7 @@ static int outstream_clear_buffer_pa(SoundIoPrivate *si,
 }
 
 static int outstream_pause_pa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os, bool pause) {
-    SoundIoOutStreamPulseAudio *ospa = (SoundIoOutStreamPulseAudio *)os->backend_data;
+    SoundIoOutStreamPulseAudio *ospa = &os->backend_data.pulseaudio;
     SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
 
     pa_threaded_mainloop_lock(sipa->main_loop);
@@ -784,7 +758,7 @@ static int outstream_pause_pa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os, b
 
 static void recording_stream_state_callback(pa_stream *stream, void *userdata) {
     SoundIoInStreamPrivate *is = (SoundIoInStreamPrivate*)userdata;
-    SoundIoInStreamPulseAudio *ispa = (SoundIoInStreamPulseAudio *)is->backend_data;
+    SoundIoInStreamPulseAudio *ispa = &is->backend_data.pulseaudio;
     SoundIoInStream *instream = &is->pub;
     SoundIo *soundio = instream->device->soundio;
     SoundIoPrivate *si = (SoundIoPrivate *)soundio;
@@ -814,11 +788,8 @@ static void recording_stream_read_callback(pa_stream *stream, size_t nbytes, voi
     instream->read_callback(instream, available_frame_count);
 }
 
-static void instream_destroy_pa(SoundIoPrivate *si, SoundIoInStreamPrivate *instream) {
+static void instream_destroy_pa(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
-    SoundIoInStreamPulseAudio *ispa = (SoundIoInStreamPulseAudio *)instream->backend_data;
+    SoundIoInStreamPulseAudio *ispa = &is->backend_data.pulseaudio;
-    if (!ispa)
-        return;
-
     SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     pa_stream *stream = ispa->stream;
     if (stream) {
@@ -836,15 +807,9 @@ static void instream_destroy_pa(SoundIoPrivate *si, SoundIoInStreamPrivate *inst
 }
 
 static int instream_open_pa(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
+    SoundIoInStreamPulseAudio *ispa = &is->backend_data.pulseaudio;
     SoundIoInStream *instream = &is->pub;
 
-    SoundIoInStreamPulseAudio *ispa = create<SoundIoInStreamPulseAudio>();
-    if (!ispa) {
-        instream_destroy_pa(si, is);
-        return SoundIoErrorNoMem;
-    }
-    is->backend_data = ispa;
-
     SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     ispa->stream_ready = false;
 
@@ -889,7 +854,7 @@ static int instream_open_pa(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
 
 static int instream_start_pa(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
     SoundIoInStream *instream = &is->pub;
-    SoundIoInStreamPulseAudio *ispa = (SoundIoInStreamPulseAudio *)is->backend_data;
+    SoundIoInStreamPulseAudio *ispa = &is->backend_data.pulseaudio;
     SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     pa_threaded_mainloop_lock(sipa->main_loop);
 
@@ -918,7 +883,7 @@ static int instream_begin_read_pa(SoundIoPrivate *si,
         SoundIoInStreamPrivate *is, SoundIoChannelArea **out_areas, int *frame_count)
 {
     SoundIoInStream *instream = &is->pub;
-    SoundIoInStreamPulseAudio *ispa = (SoundIoInStreamPulseAudio *)is->backend_data;
+    SoundIoInStreamPulseAudio *ispa = &is->backend_data.pulseaudio;
     pa_stream *stream = ispa->stream;
 
     assert(ispa->stream_ready);
@@ -948,7 +913,7 @@ static int instream_begin_read_pa(SoundIoPrivate *si,
 }
 
 static int instream_end_read_pa(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
-    SoundIoInStreamPulseAudio *ispa = (SoundIoInStreamPulseAudio *)is->backend_data;
+    SoundIoInStreamPulseAudio *ispa = &is->backend_data.pulseaudio;
     pa_stream *stream = ispa->stream;
     if (pa_stream_drop(stream))
         return SoundIoErrorStreaming;
@@ -957,7 +922,7 @@ static int instream_end_read_pa(SoundIoPrivate *si, SoundIoInStreamPrivate *is)
 }
 
 static int instream_pause_pa(SoundIoPrivate *si, SoundIoInStreamPrivate *is, bool pause) {
-    SoundIoInStreamPulseAudio *ispa = (SoundIoInStreamPulseAudio *)is->backend_data;
+    SoundIoInStreamPulseAudio *ispa = &is->backend_data.pulseaudio;
     SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
 
     pa_threaded_mainloop_lock(sipa->main_loop);

src/pulseaudio.hpp

@@ -8,6 +8,7 @@
 #ifndef SOUNDIO_PULSEAUDIO_HPP
 #define SOUNDIO_PULSEAUDIO_HPP
 
+#include "soundio.h"
 #include "atomics.hpp"
 
 #include <pulse/pulseaudio.h>
@@ -43,4 +44,19 @@ struct SoundIoPulseAudio {
     pa_proplist *props;
 };
 
+struct SoundIoOutStreamPulseAudio {
+    pa_stream *stream;
+    atomic_bool stream_ready;
+    pa_buffer_attr buffer_attr;
+    char *write_ptr;
+    SoundIoChannelArea areas[SOUNDIO_MAX_CHANNELS];
+};
+
+struct SoundIoInStreamPulseAudio {
+    pa_stream *stream;
+    atomic_bool stream_ready;
+    pa_buffer_attr buffer_attr;
+    SoundIoChannelArea areas[SOUNDIO_MAX_CHANNELS];
+};
+
 #endif

src/soundio.cpp

@@ -186,8 +186,6 @@ int soundio_connect_backend(SoundIo *soundio, SoundIoBackend backend) {
     if (!fn)
         return SoundIoErrorBackendUnavailable;
 
-    memset(&si->backend_data, 0, sizeof(SoundIoBackendData));
-
     int err;
     if ((err = backend_init_fns[backend](si))) {
         soundio_disconnect(soundio);
@@ -201,10 +199,12 @@ void soundio_disconnect(struct SoundIo *soundio) {
 
     if (si->destroy)
         si->destroy(si);
+    memset(&si->backend_data, 0, sizeof(SoundIoBackendData));
 
     soundio->current_backend = SoundIoBackendNone;
 
     soundio_destroy_devices_info(si->safe_devices_info);
+
     si->safe_devices_info = nullptr;
 
     si->destroy = nullptr;

src/soundio.hpp

@@ -51,6 +51,32 @@ union SoundIoDeviceBackendData {
     SoundIoDeviceDummy dummy;
 };
 
+union SoundIoOutStreamBackendData {
+#ifdef SOUNDIO_HAVE_JACK
+    SoundIoOutStreamJack jack;
+#endif
+#ifdef SOUNDIO_HAVE_PULSEAUDIO
+    SoundIoOutStreamPulseAudio pulseaudio;
+#endif
+#ifdef SOUNDIO_HAVE_ALSA
+    SoundIoOutStreamAlsa alsa;
+#endif
+    SoundIoOutStreamDummy dummy;
+};
+
+union SoundIoInStreamBackendData {
+#ifdef SOUNDIO_HAVE_JACK
+    SoundIoInStreamJack jack;
+#endif
+#ifdef SOUNDIO_HAVE_PULSEAUDIO
+    SoundIoInStreamPulseAudio pulseaudio;
+#endif
+#ifdef SOUNDIO_HAVE_ALSA
+    SoundIoInStreamAlsa alsa;
+#endif
+    SoundIoInStreamDummy dummy;
+};
+
 struct SoundIoDevicesInfo {
     SoundIoList<SoundIoDevice *> input_devices;
     SoundIoList<SoundIoDevice *> output_devices;
@@ -60,13 +86,13 @@ struct SoundIoDevicesInfo {
 };
 
 struct SoundIoOutStreamPrivate {
-    struct SoundIoOutStream pub;
+    SoundIoOutStream pub;
-    void *backend_data;
+    SoundIoOutStreamBackendData backend_data;
 };
 
 struct SoundIoInStreamPrivate {
-    struct SoundIoInStream pub;
+    SoundIoInStream pub;
-    void *backend_data;
+    SoundIoInStreamBackendData backend_data;
 };
 
 struct SoundIoPrivate {