SoundIo, SoundIoDevice: unions instead of void *

for better cache locality

README.md

@@ -233,12 +233,16 @@ view `coverage/index.html` in a browser.
 ## Roadmap
 
  0. implement JACK backend, get examples working
+ 0. Steal PulseAudio's default channel maps per channel count
+ 0. Ability to parse PulseAudio's "front-left" "front-right" channel label strings
+ 0. When two soundio clients are talking to each other, use port names to
+    negotiate channel maps.
  0. why does pulseaudio microphone use up all the CPU?
  0. merge in/out stream structures and functions?
  0. implement CoreAudio (OSX) backend, get examples working
  0. implement WASAPI (Windows) backend, get examples working
  0. implement ASIO (Windows) backend, get examples working
- 0. Avoid calling `panic` in PulseAudio.
+ 0. Avoid calling `soundio_panic` in PulseAudio.
  0. Figure out a way to test prebuf. I suspect prebuf not working for ALSA
     which is why we have to pre-fill the ring buffer with silence for
     the microphone example.
@@ -257,6 +261,9 @@ view `coverage/index.html` in a browser.
  0. Allow calling functions from outside the callbacks as long as they first
     call lock and then unlock when done.
  0. Should pause/resume be callable from outside the callbacks?
+ 0. device.name -> device.id, device.description -> device.name
+ 0. PulseAudio: when opening a device start it corked that way we can get
+    accurate buffer readings
  0. clean up API and improve documentation
     - make sure every function which can return an error documents which errors
       it can return

src/alsa.cpp

@@ -7,8 +7,6 @@
 
 #include "alsa.hpp"
 #include "soundio.hpp"
-#include "os.hpp"
-#include "atomics.hpp"
 
 #include <alsa/asoundlib.h>
 #include <sys/inotify.h>
@@ -25,21 +23,6 @@ static snd_pcm_access_t prioritized_access_types[] = {
 };
 
 
-struct SoundIoAlsa {
-    SoundIoOsMutex *mutex;
-    SoundIoOsCond *cond;
-
-    struct SoundIoOsThread *thread;
-    atomic_flag abort_flag;
-    int notify_fd;
-    int notify_wd;
-    atomic_bool have_devices_flag;
-    int notify_pipe_fd[2];
-
-    // this one is ready to be read with flush_events. protected by mutex
-    struct SoundIoDevicesInfo *ready_devices_info;
-};
-
 struct SoundIoOutStreamAlsa {
     snd_pcm_t *handle;
     snd_pcm_chmap_t *chmap;
@@ -85,9 +68,7 @@ static void wakeup_device_poll(SoundIoAlsa *sia) {
 }
 
 static void destroy_alsa(SoundIoPrivate *si) {
-    SoundIoAlsa *sia = (SoundIoAlsa *)si->backend_data;
+    SoundIoAlsa *sia = &si->backend_data.alsa;
-    if (!sia)
-        return;
 
     if (sia->thread) {
         sia->abort_flag.clear();
@@ -108,9 +89,6 @@ static void destroy_alsa(SoundIoPrivate *si) {
     close(sia->notify_pipe_fd[0]);
     close(sia->notify_pipe_fd[1]);
     close(sia->notify_fd);
-
-    destroy(sia);
-    si->backend_data = nullptr;
 }
 
 static char * str_partition_on_char(char *str, char c) {
@@ -517,7 +495,7 @@ static inline bool str_has_prefix(const char *big_str, const char *prefix) {
 
 static int refresh_devices(SoundIoPrivate *si) {
     SoundIo *soundio = &si->pub;
-    SoundIoAlsa *sia = (SoundIoAlsa *)si->backend_data;
+    SoundIoAlsa *sia = &si->backend_data.alsa;
 
     SoundIoDevicesInfo *devices_info = create<SoundIoDevicesInfo>();
     if (!devices_info)
@@ -761,7 +739,7 @@ static int refresh_devices(SoundIoPrivate *si) {
 
 static void device_thread_run(void *arg) {
     SoundIoPrivate *si = (SoundIoPrivate *)arg;
-    SoundIoAlsa *sia = (SoundIoAlsa *)si->backend_data;
+    SoundIoAlsa *sia = &si->backend_data.alsa;
 
     // Some systems cannot read integer variables if they are not
     // properly aligned. On other systems, incorrect alignment may
@@ -864,7 +842,7 @@ static void block_until_have_devices(SoundIoAlsa *sia) {
 
 static void flush_events(SoundIoPrivate *si) {
     SoundIo *soundio = &si->pub;
-    SoundIoAlsa *sia = (SoundIoAlsa *)si->backend_data;
+    SoundIoAlsa *sia = &si->backend_data.alsa;
     block_until_have_devices(sia);
 
     bool change = false;
@@ -888,7 +866,7 @@ static void flush_events(SoundIoPrivate *si) {
 }
 
 static void wait_events(SoundIoPrivate *si) {
-    SoundIoAlsa *sia = (SoundIoAlsa *)si->backend_data;
+    SoundIoAlsa *sia = &si->backend_data.alsa;
     flush_events(si);
     soundio_os_mutex_lock(sia->mutex);
     soundio_os_cond_wait(sia->cond, sia->mutex);
@@ -896,7 +874,7 @@ static void wait_events(SoundIoPrivate *si) {
 }
 
 static void wakeup(SoundIoPrivate *si) {
-    SoundIoAlsa *sia = (SoundIoAlsa *)si->backend_data;
+    SoundIoAlsa *sia = &si->backend_data.alsa;
     soundio_os_mutex_lock(sia->mutex);
     soundio_os_cond_signal(sia->cond, sia->mutex);
     soundio_os_mutex_unlock(sia->mutex);
@@ -1695,15 +1673,9 @@ static int instream_pause_alsa(struct SoundIoPrivate *si, struct SoundIoInStream
 }
 
 int soundio_alsa_init(SoundIoPrivate *si) {
+    SoundIoAlsa *sia = &si->backend_data.alsa;
     int err;
 
-    assert(!si->backend_data);
-    SoundIoAlsa *sia = create<SoundIoAlsa>();
-    if (!sia) {
-        destroy_alsa(si);
-        return SoundIoErrorNoMem;
-    }
-    si->backend_data = sia;
     sia->notify_fd = -1;
     sia->notify_wd = -1;
     sia->have_devices_flag.store(false);

src/alsa.hpp

@@ -8,7 +8,28 @@
 #ifndef SOUNDIO_ALSA_HPP
 #define SOUNDIO_ALSA_HPP
 
+#include "os.hpp"
+#include "atomics.hpp"
+
 int soundio_alsa_init(struct SoundIoPrivate *si);
 
-#endif
+struct SoundIoDeviceAlsa {
 
+};
+
+struct SoundIoAlsa {
+    SoundIoOsMutex *mutex;
+    SoundIoOsCond *cond;
+
+    struct SoundIoOsThread *thread;
+    atomic_flag abort_flag;
+    int notify_fd;
+    int notify_wd;
+    atomic_bool have_devices_flag;
+    int notify_pipe_fd[2];
+
+    // this one is ready to be read with flush_events. protected by mutex
+    struct SoundIoDevicesInfo *ready_devices_info;
+};
+
+#endif

src/dummy.cpp

@@ -7,7 +7,6 @@
 
 #include "dummy.hpp"
 #include "soundio.hpp"
-#include "os.hpp"
 #include "atomics.hpp"
 #include "ring_buffer.hpp"
 
@@ -39,12 +38,6 @@ struct SoundIoInStreamDummy {
     SoundIoChannelArea areas[SOUNDIO_MAX_CHANNELS];
 };
 
-struct SoundIoDummy {
-    SoundIoOsMutex *mutex;
-    SoundIoOsCond *cond;
-    bool devices_emitted;
-};
-
 static void playback_thread_run(void *arg) {
     SoundIoOutStreamPrivate *os = (SoundIoOutStreamPrivate *)arg;
     SoundIoOutStream *outstream = &os->pub;
@@ -127,23 +120,18 @@ static void capture_thread_run(void *arg) {
 }
 
 static void destroy_dummy(SoundIoPrivate *si) {
-    SoundIoDummy *sid = (SoundIoDummy *)si->backend_data;
+    SoundIoDummy *sid = &si->backend_data.dummy;
-    if (!sid)
-        return;
 
     if (sid->cond)
         soundio_os_cond_destroy(sid->cond);
 
     if (sid->mutex)
         soundio_os_mutex_destroy(sid->mutex);
-
-    destroy(sid);
-    si->backend_data = nullptr;
 }
 
 static void flush_events(SoundIoPrivate *si) {
     SoundIo *soundio = &si->pub;
-    SoundIoDummy *sid = (SoundIoDummy *)si->backend_data;
+    SoundIoDummy *sid = &si->backend_data.dummy;
     if (sid->devices_emitted)
         return;
     sid->devices_emitted = true;
@@ -151,13 +139,13 @@ static void flush_events(SoundIoPrivate *si) {
 }
 
 static void wait_events(SoundIoPrivate *si) {
-    SoundIoDummy *sid = (SoundIoDummy *)si->backend_data;
+    SoundIoDummy *sid = &si->backend_data.dummy;
     flush_events(si);
     soundio_os_cond_wait(sid->cond, nullptr);
 }
 
 static void wakeup(SoundIoPrivate *si) {
-    SoundIoDummy *sid = (SoundIoDummy *)si->backend_data;
+    SoundIoDummy *sid = &si->backend_data.dummy;
     soundio_os_cond_signal(sid->cond, nullptr);
 }
 
@@ -468,13 +456,7 @@ static int set_all_device_channel_layouts(SoundIoDevice *device) {
 
 int soundio_dummy_init(SoundIoPrivate *si) {
     SoundIo *soundio = &si->pub;
-    assert(!si->backend_data);
+    SoundIoDummy *sid = &si->backend_data.dummy;
-    SoundIoDummy *sid = create<SoundIoDummy>();
-    if (!sid) {
-        destroy_dummy(si);
-        return SoundIoErrorNoMem;
-    }
-    si->backend_data = sid;
 
     sid->mutex = soundio_os_mutex_create();
     if (!sid->mutex) {

src/dummy.hpp

@@ -8,6 +8,18 @@
 #ifndef SOUNDIO_DUMMY_HPP
 #define SOUNDIO_DUMMY_HPP
 
+#include "os.hpp"
+
 int soundio_dummy_init(struct SoundIoPrivate *si);
 
+struct SoundIoDummy {
+    SoundIoOsMutex *mutex;
+    SoundIoOsCond *cond;
+    bool devices_emitted;
+};
+
+struct SoundIoDeviceDummy {
+
+};
+
 #endif

src/jack.cpp

@@ -8,23 +8,15 @@
 #include "jack.hpp"
 #include "soundio.hpp"
 #include "atomics.hpp"
-#include "os.hpp"
 #include "list.hpp"
 
-#include <jack/jack.h>
 #include <stdio.h>
 
 static atomic_flag global_msg_callback_flag = ATOMIC_FLAG_INIT;
 
-struct SoundIoJack {
+struct SoundIoOutStreamJack {
     jack_client_t *client;
-    SoundIoOsMutex *mutex;
+    jack_port_t *ports[SOUNDIO_MAX_CHANNELS];
-    SoundIoOsCond *cond;
-    // this one is ready to be read with flush_events. protected by mutex
-    struct SoundIoDevicesInfo *ready_devices_info;
-    bool initialized;
-    int sample_rate;
-    int buffer_size;
 };
 
 struct SoundIoJackPort {
@@ -37,12 +29,13 @@ struct SoundIoJackClient {
     int name_len;
     bool is_physical;
     SoundIoDevicePurpose purpose;
-    SoundIoList<SoundIoJackPort> ports;
+    SoundIoJackPort ports[SOUNDIO_MAX_CHANNELS];
+    int port_count;
 };
 
 static void flush_events_jack(struct SoundIoPrivate *si) {
     SoundIo *soundio = &si->pub;
-    SoundIoJack *sij = (SoundIoJack *)si->backend_data;
+    SoundIoJack *sij = &si->backend_data.jack;
 
     bool change = false;
     SoundIoDevicesInfo *old_devices_info = nullptr;
@@ -65,7 +58,7 @@ static void flush_events_jack(struct SoundIoPrivate *si) {
 }
 
 static void wait_events_jack(struct SoundIoPrivate *si) {
-    SoundIoJack *sij = (SoundIoJack *)si->backend_data;
+    SoundIoJack *sij = &si->backend_data.jack;
     flush_events_jack(si);
     soundio_os_mutex_lock(sij->mutex);
     soundio_os_cond_wait(sij->cond, sij->mutex);
@@ -73,69 +66,150 @@ static void wait_events_jack(struct SoundIoPrivate *si) {
 }
 
 static void wakeup_jack(struct SoundIoPrivate *si) {
-    SoundIoJack *sij = (SoundIoJack *)si->backend_data;
+    SoundIoJack *sij = &si->backend_data.jack;
     soundio_os_mutex_lock(sij->mutex);
     soundio_os_cond_signal(sij->cond, sij->mutex);
     soundio_os_mutex_unlock(sij->mutex);
 }
 
-
+static int outstream_process_callback(jack_nframes_t nframes, void *arg) {
-static int outstream_open_jack(struct SoundIoPrivate *, struct SoundIoOutStreamPrivate *) {
+    SoundIoOutStreamPrivate *os = (SoundIoOutStreamPrivate *)arg;
-    soundio_panic("TODO");
+    SoundIoOutStream *outstream = &os->pub;
+    outstream->write_callback(outstream, nframes);
+    return 0;
 }
 
-static void outstream_destroy_jack(struct SoundIoPrivate *, struct SoundIoOutStreamPrivate *) {
+static void outstream_destroy_jack(struct SoundIoPrivate *is, struct SoundIoOutStreamPrivate *os) {
-    soundio_panic("TODO");
+    SoundIoOutStreamJack *osj = (SoundIoOutStreamJack *) os->backend_data;
+    if (!osj)
+        return;
+
+    jack_client_close(osj->client);
+
+    destroy(osj);
+    os->backend_data = nullptr;
 }
 
-static int outstream_start_jack(struct SoundIoPrivate *, struct SoundIoOutStreamPrivate *) {
+static int outstream_open_jack(struct SoundIoPrivate *si, struct SoundIoOutStreamPrivate *os) {
-    soundio_panic("TODO");
+    SoundIoOutStream *outstream = &os->pub;
+    //TODO SoundIoDevice *device = outstream->device;
+
+    outstream->buffer_duration = 0.0; // TODO
+    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;
+    osj->client = jack_client_open(outstream->name, JackNoStartServer, &status);
+    if (!osj->client) {
+        outstream_destroy_jack(si, os);
+        assert(!(status & JackInvalidOption));
+        if (status & JackShmFailure)
+            return SoundIoErrorSystemResources;
+        if (status & JackNoSuchClient)
+            return SoundIoErrorNoSuchClient;
+        return SoundIoErrorOpeningDevice;
+    }
+
+    int err;
+    if ((err = jack_set_process_callback(osj->client, outstream_process_callback, os))) {
+        outstream_destroy_jack(si, os);
+        return SoundIoErrorOpeningDevice;
+    }
+    // TODO register the other callbacks and emit a stream error if they're called
+
+
+    // register ports
+    for (int ch = 0; ch < outstream->layout.channel_count; ch += 1) {
+        const char *channel_name = soundio_get_channel_name(outstream->layout.channels[ch]);
+        unsigned long flags = JackPortIsOutput;
+        if (!outstream->non_terminal_hint)
+            flags |= JackPortIsTerminal;
+        jack_port_t *port = jack_port_register(osj->client, channel_name, JACK_DEFAULT_AUDIO_TYPE, flags, 0);
+        if (!port) {
+            outstream_destroy_jack(si, os);
+            return SoundIoErrorOpeningDevice;
+        }
+        osj->ports[ch] = port;
+    }
+
+    return 0;
+}
+
+static int outstream_pause_jack(struct SoundIoPrivate *si, struct SoundIoOutStreamPrivate *os, bool pause) {
+    SoundIoOutStreamJack *osj = (SoundIoOutStreamJack *) os->backend_data;
+    SoundIoOutStream *outstream = &os->pub;
+    int err;
+    if (pause) {
+        if ((err = jack_deactivate(osj->client)))
+            return SoundIoErrorStreaming;
+    } else {
+        if ((err = jack_activate(osj->client)))
+            return SoundIoErrorStreaming;
+
+        for (int ch = 0; ch < outstream->layout.channel_count; ch += 1) {
+            // TODO figure out source port name and dest port name
+            //if ((err = jack_connect(osj->client, source_port, dest_port)))
+            //    return SoundIoErrorStreaming;
+        }
+    }
+
+    return 0;
+}
+
+static int outstream_start_jack(struct SoundIoPrivate *si, struct SoundIoOutStreamPrivate *os) {
+    return outstream_pause_jack(si, os, false);
 }
 
 static int outstream_begin_write_jack(struct SoundIoPrivate *, struct SoundIoOutStreamPrivate *,
         SoundIoChannelArea **out_areas, int *frame_count)
 {
-    soundio_panic("TODO");
+    soundio_panic("TODO begin write");
 }
 
 static int outstream_end_write_jack(struct SoundIoPrivate *, struct SoundIoOutStreamPrivate *, int frame_count) {
-    soundio_panic("TODO");
+    soundio_panic("TODO end write");
 }
 
 static int outstream_clear_buffer_jack(struct SoundIoPrivate *, struct SoundIoOutStreamPrivate *) {
-    soundio_panic("TODO");
+    soundio_panic("TODO clear buffer");
 }
 
-static int outstream_pause_jack(struct SoundIoPrivate *, struct SoundIoOutStreamPrivate *, bool pause) {
-    soundio_panic("TODO");
-}
 
 
 
 static int instream_open_jack(struct SoundIoPrivate *, struct SoundIoInStreamPrivate *) {
-    soundio_panic("TODO");
+    soundio_panic("TODO open instream");
 }
 
 static void instream_destroy_jack(struct SoundIoPrivate *, struct SoundIoInStreamPrivate *) {
-    soundio_panic("TODO");
+    soundio_panic("TODO destroy instream");
 }
 
 static int instream_start_jack(struct SoundIoPrivate *, struct SoundIoInStreamPrivate *) {
-    soundio_panic("TODO");
+    soundio_panic("TODO start instream");
 }
 
 static int instream_begin_read_jack(struct SoundIoPrivate *, struct SoundIoInStreamPrivate *,
         SoundIoChannelArea **out_areas, int *frame_count)
 {
-    soundio_panic("TODO");
+    soundio_panic("TODO begin read");
 }
 
 static int instream_end_read_jack(struct SoundIoPrivate *, struct SoundIoInStreamPrivate *) {
-    soundio_panic("TODO");
+    soundio_panic("TODO end read");
 }
 
 static int instream_pause_jack(struct SoundIoPrivate *, struct SoundIoInStreamPrivate *, bool pause) {
-    soundio_panic("TODO");
+    soundio_panic("TODO pause");
 }
 
 static void split_str(const char *input_str, int input_str_len, char c,
@@ -179,6 +253,7 @@ static SoundIoJackClient *find_or_create_client(SoundIoList<SoundIoJackClient> *
     client->purpose = purpose;
     client->name = client_name;
     client->name_len = client_name_len;
+    client->port_count = 0;
     return client;
 }
 
@@ -193,7 +268,7 @@ static char *dupe_str(const char *str, int str_len) {
 
 static int refresh_devices(SoundIoPrivate *si) {
     SoundIo *soundio = &si->pub;
-    SoundIoJack *sij = (SoundIoJack *)si->backend_data;
+    SoundIoJack *sij = &si->backend_data.jack;
 
     SoundIoDevicesInfo *devices_info = create<SoundIoDevicesInfo>();
     if (!devices_info)
@@ -208,13 +283,18 @@ static int refresh_devices(SoundIoPrivate *si) {
     }
 
     SoundIoList<SoundIoJackClient> clients;
-    int err;
-
     const char **port_name_ptr = port_names;
     while (*port_name_ptr) {
         const char *client_and_port_name = *port_name_ptr;
         jack_port_t *jport = jack_port_by_name(sij->client, client_and_port_name);
         int flags = jack_port_flags(jport);
+
+        const char *port_type = jack_port_type(jport);
+        if (strcmp(port_type, JACK_DEFAULT_AUDIO_TYPE) != 0) {
+            // we don't know how to support such a port
+            continue;
+        }
+
         SoundIoDevicePurpose purpose = (flags & JackPortIsInput) ?
             SoundIoDevicePurposeOutput : SoundIoDevicePurposeInput;
         bool is_physical = flags & JackPortIsPhysical;
@@ -236,12 +316,11 @@ static int refresh_devices(SoundIoPrivate *si) {
             destroy(devices_info);
             return SoundIoErrorNoMem;
         }
-        if ((err = client->ports.add_one())) {
+        if (client->port_count >= SOUNDIO_MAX_CHANNELS) {
-            jack_free(port_names);
+            // we hit the channel limit, skip the leftovers
-            destroy(devices_info);
+            continue;
-            return SoundIoErrorNoMem;
         }
-        SoundIoJackPort *port = &client->ports.last();
+        SoundIoJackPort *port = &client->ports[client->port_count++];
         port->name = port_name;
         port->name_len = port_name_len;
 
@@ -251,7 +330,7 @@ static int refresh_devices(SoundIoPrivate *si) {
 
     for (int i = 0; i < clients.length; i += 1) {
         SoundIoJackClient *client = &clients.at(i);
-        if (client->ports.length <= 0)
+        if (client->port_count <= 0)
             continue;
 
         SoundIoDevice *device = create<SoundIoDevice>();
@@ -260,9 +339,9 @@ static int refresh_devices(SoundIoPrivate *si) {
             destroy(devices_info);
             return SoundIoErrorNoMem;
         }
-        int description_len = client->name_len + 3 + 2 * client->ports.length;
+        int description_len = client->name_len + 3 + 2 * client->port_count;
-        for (int port_index = 0; port_index < client->ports.length; port_index += 1) {
+        for (int port_index = 0; port_index < client->port_count; port_index += 1) {
-            SoundIoJackPort *port = &client->ports.at(port_index);
+            SoundIoJackPort *port = &client->ports[port_index];
             description_len += port->name_len;
         }
 
@@ -294,21 +373,21 @@ static int refresh_devices(SoundIoPrivate *si) {
         memcpy(device->description, client->name, client->name_len);
         memcpy(&device->description[client->name_len], ": ", 2);
         int index = client->name_len + 2;
-        for (int port_index = 0; port_index < client->ports.length; port_index += 1) {
+        for (int port_index = 0; port_index < client->port_count; port_index += 1) {
-            SoundIoJackPort *port = &client->ports.at(port_index);
+            SoundIoJackPort *port = &client->ports[port_index];
             memcpy(&device->description[index], port->name, port->name_len);
             index += port->name_len;
-            if (port_index + 1 < client->ports.length) {
+            if (port_index + 1 < client->port_count) {
                 memcpy(&device->description[index], ", ", 2);
                 index += 2;
             }
         }
 
-        const struct SoundIoChannelLayout *layout = soundio_channel_layout_get_default(client->ports.length);
+        const struct SoundIoChannelLayout *layout = soundio_channel_layout_get_default(client->port_count);
         if (layout) {
             device->current_layout = *layout;
         } else {
-            for (int port_index = 0; port_index < client->ports.length; port_index += 1)
+            for (int port_index = 0; port_index < client->port_count; port_index += 1)
                 device->current_layout.channels[port_index] = SoundIoChannelIdInvalid;
         }
 
@@ -355,7 +434,7 @@ static int process_callback(jack_nframes_t nframes, void *arg) {
 
 static int buffer_size_callback(jack_nframes_t nframes, void *arg) {
     SoundIoPrivate *si = (SoundIoPrivate *)arg;
-    SoundIoJack *sij = (SoundIoJack *)si->backend_data;
+    SoundIoJack *sij = &si->backend_data.jack;
     sij->buffer_size = nframes;
     if (sij->initialized)
         refresh_devices(si);
@@ -364,7 +443,7 @@ static int buffer_size_callback(jack_nframes_t nframes, void *arg) {
 
 static int sample_rate_callback(jack_nframes_t nframes, void *arg) {
     SoundIoPrivate *si = (SoundIoPrivate *)arg;
-    SoundIoJack *sij = (SoundIoJack *)si->backend_data;
+    SoundIoJack *sij = &si->backend_data.jack;
     sij->sample_rate = nframes;
     if (sij->initialized)
         refresh_devices(si);
@@ -379,7 +458,7 @@ static int xrun_callback(void *arg) {
 
 static void port_registration_callback(jack_port_id_t port_id, int reg, void *arg) {
     SoundIoPrivate *si = (SoundIoPrivate *)arg;
-    SoundIoJack *sij = (SoundIoJack *)si->backend_data;
+    SoundIoJack *sij = &si->backend_data.jack;
     if (sij->initialized)
         refresh_devices(si);
 }
@@ -388,7 +467,7 @@ static int port_rename_calllback(jack_port_id_t port_id,
         const char *old_name, const char *new_name, void *arg)
 {
     SoundIoPrivate *si = (SoundIoPrivate *)arg;
-    SoundIoJack *sij = (SoundIoJack *)si->backend_data;
+    SoundIoJack *sij = &si->backend_data.jack;
     if (sij->initialized)
         refresh_devices(si);
     return 0;
@@ -400,9 +479,7 @@ static void shutdown_callback(void *arg) {
 }
 
 static void destroy_jack(SoundIoPrivate *si) {
-    SoundIoJack *sij = (SoundIoJack *)si->backend_data;
+    SoundIoJack *sij = &si->backend_data.jack;
-    if (!sij)
-        return;
 
     if (sij->client)
         jack_client_close(sij->client);
@@ -414,12 +491,10 @@ static void destroy_jack(SoundIoPrivate *si) {
         soundio_os_mutex_destroy(sij->mutex);
 
     soundio_destroy_devices_info(sij->ready_devices_info);
-
-    destroy(sij);
-    si->backend_data = nullptr;
 }
 
 int soundio_jack_init(struct SoundIoPrivate *si) {
+    SoundIoJack *sij = &si->backend_data.jack;
     SoundIo *soundio = &si->pub;
 
     if (!global_msg_callback_flag.test_and_set()) {
@@ -430,14 +505,6 @@ int soundio_jack_init(struct SoundIoPrivate *si) {
         global_msg_callback_flag.clear();
     }
 
-    assert(!si->backend_data);
-    SoundIoJack *sij = create<SoundIoJack>();
-    if (!sij) {
-        destroy_jack(si);
-        return SoundIoErrorNoMem;
-    }
-    si->backend_data = sij;
-
     sij->mutex = soundio_os_mutex_create();
     if (!sij->mutex) {
         destroy_jack(si);

src/jack.hpp

@@ -8,7 +8,26 @@
 #ifndef SOUNDIO_JACK_HPP
 #define SOUNDIO_JACK_HPP
 
+#include "os.hpp"
+
+#include <jack/jack.h>
+
 int soundio_jack_init(struct SoundIoPrivate *si);
 
+struct SoundIoDeviceJack {
+
+};
+
+struct SoundIoJack {
+    jack_client_t *client;
+    SoundIoOsMutex *mutex;
+    SoundIoOsCond *cond;
+    // this one is ready to be read with flush_events. protected by mutex
+    struct SoundIoDevicesInfo *ready_devices_info;
+    bool initialized;
+    int sample_rate;
+    int buffer_size;
+};
+
 #endif
 

src/pulseaudio.cpp

@@ -7,13 +7,11 @@
 
 #include "pulseaudio.hpp"
 #include "soundio.hpp"
-#include "atomics.hpp"
 
 #include <string.h>
 #include <math.h>
 #include <stdio.h>
 
-#include <pulse/pulseaudio.h>
 
 struct SoundIoOutStreamPulseAudio {
     pa_stream *stream;
@@ -30,43 +28,17 @@ struct SoundIoInStreamPulseAudio {
     SoundIoChannelArea areas[SOUNDIO_MAX_CHANNELS];
 };
 
-struct SoundIoPulseAudio {
-    bool connection_refused;
-
-    pa_context *pulse_context;
-    atomic_bool device_scan_queued;
-
-    // the one that we're working on building
-    struct SoundIoDevicesInfo *current_devices_info;
-    char * default_sink_name;
-    char * default_source_name;
-
-    // this one is ready to be read with flush_events. protected by mutex
-    struct SoundIoDevicesInfo *ready_devices_info;
-
-    bool have_sink_list;
-    bool have_source_list;
-    bool have_default_sink;
-
-    atomic_bool ready_flag;
-    atomic_bool have_devices_flag;
-
-    pa_threaded_mainloop *main_loop;
-    pa_proplist *props;
-};
-
-
 static void subscribe_callback(pa_context *context,
         pa_subscription_event_type_t event_bits, uint32_t index, void *userdata)
 {
     SoundIoPrivate *si = (SoundIoPrivate *)userdata;
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     sipa->device_scan_queued = true;
     pa_threaded_mainloop_signal(sipa->main_loop, 0);
 }
 
 static void subscribe_to_events(SoundIoPrivate *si) {
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     pa_subscription_mask_t events = (pa_subscription_mask_t)(
             PA_SUBSCRIPTION_MASK_SINK|PA_SUBSCRIPTION_MASK_SOURCE|PA_SUBSCRIPTION_MASK_SERVER);
     pa_operation *subscribe_op = pa_context_subscribe(sipa->pulse_context,
@@ -78,7 +50,7 @@ static void subscribe_to_events(SoundIoPrivate *si) {
 
 static void context_state_callback(pa_context *context, void *userdata) {
     SoundIoPrivate *si = (SoundIoPrivate *)userdata;
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
 
     switch (pa_context_get_state(context)) {
     case PA_CONTEXT_UNCONNECTED: // The context hasn't been connected yet.
@@ -112,9 +84,7 @@ static void context_state_callback(pa_context *context, void *userdata) {
 }
 
 static void destroy_pa(SoundIoPrivate *si) {
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
-    if (!sipa)
-        return;
 
     if (sipa->main_loop)
         pa_threaded_mainloop_stop(sipa->main_loop);
@@ -133,9 +103,6 @@ static void destroy_pa(SoundIoPrivate *si) {
 
     free(sipa->default_sink_name);
     free(sipa->default_source_name);
-
-    destroy(sipa);
-    si->backend_data = nullptr;
 }
 
 static SoundIoFormat from_pulseaudio_format(pa_sample_spec sample_spec) {
@@ -232,7 +199,7 @@ static int set_all_device_formats(SoundIoDevice *device) {
 }
 
 static int perform_operation(SoundIoPrivate *si, pa_operation *op) {
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     for (;;) {
         switch (pa_operation_get_state(op)) {
         case PA_OPERATION_RUNNING:
@@ -250,7 +217,7 @@ static int perform_operation(SoundIoPrivate *si, pa_operation *op) {
 
 static void finish_device_query(SoundIoPrivate *si) {
     SoundIo *soundio = &si->pub;
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
 
     if (!sipa->have_sink_list ||
         !sipa->have_source_list ||
@@ -298,7 +265,7 @@ static void finish_device_query(SoundIoPrivate *si) {
 static void sink_info_callback(pa_context *pulse_context, const pa_sink_info *info, int eol, void *userdata) {
     SoundIoPrivate *si = (SoundIoPrivate *)userdata;
     SoundIo *soundio = &si->pub;
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     int err;
     if (eol) {
         sipa->have_sink_list = true;
@@ -348,7 +315,7 @@ static void sink_info_callback(pa_context *pulse_context, const pa_sink_info *in
 static void source_info_callback(pa_context *pulse_context, const pa_source_info *info, int eol, void *userdata) {
     SoundIoPrivate *si = (SoundIoPrivate *)userdata;
     SoundIo *soundio = &si->pub;
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     int err;
     if (eol) {
         sipa->have_source_list = true;
@@ -399,7 +366,7 @@ static void source_info_callback(pa_context *pulse_context, const pa_source_info
 static void server_info_callback(pa_context *pulse_context, const pa_server_info *info, void *userdata) {
     SoundIoPrivate *si = (SoundIoPrivate *)userdata;
     assert(si);
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
 
     free(sipa->default_sink_name);
     free(sipa->default_source_name);
@@ -416,7 +383,7 @@ static void server_info_callback(pa_context *pulse_context, const pa_server_info
 }
 
 static void scan_devices(SoundIoPrivate *si) {
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
 
     sipa->have_sink_list = false;
     sipa->have_default_sink = false;
@@ -449,7 +416,7 @@ static void scan_devices(SoundIoPrivate *si) {
 }
 
 static void block_until_have_devices(SoundIoPrivate *si) {
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     if (sipa->have_devices_flag)
         return;
     pa_threaded_mainloop_lock(sipa->main_loop);
@@ -460,7 +427,7 @@ static void block_until_have_devices(SoundIoPrivate *si) {
 }
 
 static void block_until_ready(SoundIoPrivate *si) {
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     if (sipa->ready_flag)
         return;
     pa_threaded_mainloop_lock(sipa->main_loop);
@@ -474,7 +441,7 @@ static void flush_events(SoundIoPrivate *si) {
     SoundIo *soundio = &si->pub;
     block_until_ready(si);
 
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
 
     if (sipa->device_scan_queued) {
         sipa->device_scan_queued = false;
@@ -504,13 +471,13 @@ static void flush_events(SoundIoPrivate *si) {
 }
 
 static void wait_events(SoundIoPrivate *si) {
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     flush_events(si);
     pa_threaded_mainloop_wait(sipa->main_loop);
 }
 
 static void wakeup(SoundIoPrivate *si) {
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     pa_threaded_mainloop_signal(sipa->main_loop, 0);
 }
 
@@ -602,7 +569,7 @@ static void playback_stream_state_callback(pa_stream *stream, void *userdata) {
     SoundIoOutStream *outstream = &os->pub;
     SoundIo *soundio = outstream->device->soundio;
     SoundIoPrivate *si = (SoundIoPrivate *)soundio;
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     SoundIoOutStreamPulseAudio *ospa = (SoundIoOutStreamPulseAudio *)os->backend_data;
     switch (pa_stream_get_state(stream)) {
         case PA_STREAM_UNCONNECTED:
@@ -635,7 +602,7 @@ static void outstream_destroy_pa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os
     if (!ospa)
         return;
 
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     pa_stream *stream = ospa->stream;
     if (stream) {
         pa_threaded_mainloop_lock(sipa->main_loop);
@@ -666,7 +633,7 @@ static int outstream_open_pa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os) {
     }
     os->backend_data = ospa;
 
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     ospa->stream_ready = false;
 
     assert(sipa->pulse_context);
@@ -718,7 +685,7 @@ static int outstream_open_pa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os) {
 
 static int outstream_start_pa(SoundIoPrivate *si, SoundIoOutStreamPrivate *os) {
     SoundIoOutStream *outstream = &os->pub;
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     SoundIoOutStreamPulseAudio *ospa = (SoundIoOutStreamPulseAudio *)os->backend_data;
 
     pa_threaded_mainloop_lock(sipa->main_loop);
@@ -786,7 +753,7 @@ static int outstream_clear_buffer_pa(SoundIoPrivate *si,
         SoundIoOutStreamPrivate *os)
 {
     SoundIoOutStreamPulseAudio *ospa = (SoundIoOutStreamPulseAudio *)os->backend_data;
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     pa_stream *stream = ospa->stream;
     pa_threaded_mainloop_lock(sipa->main_loop);
     pa_operation *op = pa_stream_flush(stream, NULL, NULL);
@@ -799,7 +766,7 @@ 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;
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
 
     pa_threaded_mainloop_lock(sipa->main_loop);
 
@@ -821,7 +788,7 @@ static void recording_stream_state_callback(pa_stream *stream, void *userdata) {
     SoundIoInStream *instream = &is->pub;
     SoundIo *soundio = instream->device->soundio;
     SoundIoPrivate *si = (SoundIoPrivate *)soundio;
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     switch (pa_stream_get_state(stream)) {
         case PA_STREAM_UNCONNECTED:
         case PA_STREAM_CREATING:
@@ -852,7 +819,7 @@ static void instream_destroy_pa(SoundIoPrivate *si, SoundIoInStreamPrivate *inst
     if (!ispa)
         return;
 
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     pa_stream *stream = ispa->stream;
     if (stream) {
         pa_threaded_mainloop_lock(sipa->main_loop);
@@ -878,7 +845,7 @@ static int instream_open_pa(SoundIoPrivate *si, SoundIoInStreamPrivate *is) {
     }
     is->backend_data = ispa;
 
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     ispa->stream_ready = false;
 
     pa_threaded_mainloop_lock(sipa->main_loop);
@@ -923,7 +890,7 @@ 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;
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
     pa_threaded_mainloop_lock(sipa->main_loop);
 
     pa_stream_flags_t flags = (instream->period_duration > 0.0) ? PA_STREAM_ADJUST_LATENCY : PA_STREAM_NOFLAGS;
@@ -991,7 +958,7 @@ 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;
-    SoundIoPulseAudio *sipa = (SoundIoPulseAudio *)si->backend_data;
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
 
     pa_threaded_mainloop_lock(sipa->main_loop);
 
@@ -1009,14 +976,7 @@ static int instream_pause_pa(SoundIoPrivate *si, SoundIoInStreamPrivate *is, boo
 
 int soundio_pulseaudio_init(SoundIoPrivate *si) {
     SoundIo *soundio = &si->pub;
-
+    SoundIoPulseAudio *sipa = &si->backend_data.pulseaudio;
-    assert(!si->backend_data);
-    SoundIoPulseAudio *sipa = create<SoundIoPulseAudio>();
-    if (!sipa) {
-        destroy_pa(si);
-        return SoundIoErrorNoMem;
-    }
-    si->backend_data = sipa;
 
     sipa->connection_refused = false;
     sipa->device_scan_queued = false;

src/pulseaudio.hpp

@@ -8,6 +8,39 @@
 #ifndef SOUNDIO_PULSEAUDIO_HPP
 #define SOUNDIO_PULSEAUDIO_HPP
 
+#include "atomics.hpp"
+
+#include <pulse/pulseaudio.h>
+
 int soundio_pulseaudio_init(struct SoundIoPrivate *si);
 
+struct SoundIoDevicePulseAudio {
+
+};
+
+struct SoundIoPulseAudio {
+    bool connection_refused;
+
+    pa_context *pulse_context;
+    atomic_bool device_scan_queued;
+
+    // the one that we're working on building
+    struct SoundIoDevicesInfo *current_devices_info;
+    char *default_sink_name;
+    char *default_source_name;
+
+    // this one is ready to be read with flush_events. protected by mutex
+    struct SoundIoDevicesInfo *ready_devices_info;
+
+    bool have_sink_list;
+    bool have_source_list;
+    bool have_default_sink;
+
+    atomic_bool ready_flag;
+    atomic_bool have_devices_flag;
+
+    pa_threaded_mainloop *main_loop;
+    pa_proplist *props;
+};
+
 #endif

src/soundio.cpp

@@ -7,22 +7,9 @@
 
 #include "soundio.hpp"
 #include "util.hpp"
-#include "dummy.hpp"
 #include "os.hpp"
 #include "config.h"
 
-#ifdef SOUNDIO_HAVE_JACK
-#include "jack.hpp"
-#endif
-
-#ifdef SOUNDIO_HAVE_PULSEAUDIO
-#include "pulseaudio.hpp"
-#endif
-
-#ifdef SOUNDIO_HAVE_ALSA
-#include "alsa.hpp"
-#endif
-
 #include <string.h>
 #include <assert.h>
 
@@ -71,6 +58,7 @@ const char *soundio_strerror(int error) {
         case SoundIoErrorStreaming: return "unrecoverable streaming failure";
         case SoundIoErrorIncompatibleDevice: return "incompatible device";
         case SoundIoErrorNoSuchClient: return "no such client";
+        case SoundIoErrorIncompatibleBackend: return "incompatible backend";
     }
     soundio_panic("invalid error enum value: %d", error);
 }
@@ -198,6 +186,8 @@ 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);
@@ -211,7 +201,6 @@ void soundio_disconnect(struct SoundIo *soundio) {
 
     if (si->destroy)
         si->destroy(si);
-    assert(!si->backend_data);
 
     soundio->current_backend = SoundIoBackendNone;
 

src/soundio.h

@@ -27,6 +27,7 @@ enum SoundIoError {
     SoundIoErrorStreaming,
     SoundIoErrorIncompatibleDevice,
     SoundIoErrorNoSuchClient,
+    SoundIoErrorIncompatibleBackend,
 };
 
 enum SoundIoChannelId {
@@ -210,6 +211,7 @@ struct SoundIo {
     // Optional: Application name.
     // PulseAudio uses this for "application name".
     // JACK uses this for `client_name`.
+    // Must not contain a colon (":").
     const char *app_name;
 
     // Optional: JACK info and error callbacks.
@@ -371,8 +373,14 @@ struct SoundIoOutStream {
     // PulseAudio uses this for the stream name.
     // JACK uses this for the client name of the client that connects when you
     // open the stream.
+    // Must not contain a colon (":").
     const char *name;
 
+    // Optional: Hint that this output stream is nonterminal. This is used by
+    // JACK and it means that the output stream data originates from an input
+    // stream. Defaults to `false`.
+    bool non_terminal_hint;
+
 
     // computed automatically when you call soundio_outstream_open
     int bytes_per_frame;
@@ -425,6 +433,7 @@ struct SoundIoInStream {
     // PulseAudio uses this for the stream name.
     // JACK uses this for the client name of the client that connects when you
     // open the stream.
+    // Must not contain a colon (":").
     const char *name;
 
     // computed automatically when you call soundio_instream_open

src/soundio.hpp

@@ -11,6 +11,46 @@
 #include "soundio.h"
 #include "list.hpp"
 
+#ifdef SOUNDIO_HAVE_JACK
+#include "jack.hpp"
+#endif
+
+#ifdef SOUNDIO_HAVE_PULSEAUDIO
+#include "pulseaudio.hpp"
+#endif
+
+#ifdef SOUNDIO_HAVE_ALSA
+#include "alsa.hpp"
+#endif
+
+#include "dummy.hpp"
+
+union SoundIoBackendData {
+#ifdef SOUNDIO_HAVE_JACK
+    SoundIoJack jack;
+#endif
+#ifdef SOUNDIO_HAVE_PULSEAUDIO
+    SoundIoPulseAudio pulseaudio;
+#endif
+#ifdef SOUNDIO_HAVE_ALSA
+    SoundIoAlsa alsa;
+#endif
+    SoundIoDummy dummy;
+};
+
+union SoundIoDeviceBackendData {
+#ifdef SOUNDIO_HAVE_JACK
+    SoundIoDeviceJack jack;
+#endif
+#ifdef SOUNDIO_HAVE_PULSEAUDIO
+    SoundIoDevicePulseAudio pulseaudio;
+#endif
+#ifdef SOUNDIO_HAVE_ALSA
+    SoundIoDeviceAlsa alsa;
+#endif
+    SoundIoDeviceDummy dummy;
+};
+
 struct SoundIoDevicesInfo {
     SoundIoList<SoundIoDevice *> input_devices;
     SoundIoList<SoundIoDevice *> output_devices;
@@ -35,7 +75,7 @@ struct SoundIoPrivate {
     // Safe to read from a single thread without a mutex.
     struct SoundIoDevicesInfo *safe_devices_info;
 
-    void *backend_data;
+    SoundIoBackendData backend_data;
     void (*destroy)(struct SoundIoPrivate *);
     void (*flush_events)(struct SoundIoPrivate *);
     void (*wait_events)(struct SoundIoPrivate *);
@@ -60,6 +100,11 @@ struct SoundIoPrivate {
     int (*instream_pause)(struct SoundIoPrivate *, struct SoundIoInStreamPrivate *, bool pause);
 };
 
+struct SoundIoDevicePrivate {
+    SoundIoDevice pub;
+    SoundIoDeviceBackendData backend_data;
+};
+
 void soundio_destroy_devices_info(struct SoundIoDevicesInfo *devices_info);