Add m-esr52 at 52.6.0

1 files changed, 1149 insertions, 0 deletions

diff --git a/media/libcubeb/src/cubeb_alsa.c b/media/libcubeb/src/cubeb_alsa.c
new file mode 100644
index 000000000..1ea0961d0
--- /dev/null
+++ b/media/libcubeb/src/cubeb_alsa.c
@@ -0,0 +1,1149 @@
+/*
+ * Copyright © 2011 Mozilla Foundation
+ *
+ * This program is made available under an ISC-style license.  See the
+ * accompanying file LICENSE for details.
+ */
+#undef NDEBUG
+#define _DEFAULT_SOURCE
+#define _BSD_SOURCE
+#define _XOPEN_SOURCE 500
+#include <pthread.h>
+#include <sys/time.h>
+#include <assert.h>
+#include <limits.h>
+#include <poll.h>
+#include <unistd.h>
+#include <alsa/asoundlib.h>
+#include "cubeb/cubeb.h"
+#include "cubeb-internal.h"
+
+#define CUBEB_STREAM_MAX 16
+#define CUBEB_WATCHDOG_MS 10000
+
+#define CUBEB_ALSA_PCM_NAME "default"
+
+#define ALSA_PA_PLUGIN "ALSA <-> PulseAudio PCM I/O Plugin"
+
+/* ALSA is not thread-safe.  snd_pcm_t instances are individually protected
+   by the owning cubeb_stream's mutex.  snd_pcm_t creation and destruction
+   is not thread-safe until ALSA 1.0.24 (see alsa-lib.git commit 91c9c8f1),
+   so those calls must be wrapped in the following mutex. */
+static pthread_mutex_t cubeb_alsa_mutex = PTHREAD_MUTEX_INITIALIZER;
+static int cubeb_alsa_error_handler_set = 0;
+
+static struct cubeb_ops const alsa_ops;
+
+struct cubeb {
+  struct cubeb_ops const * ops;
+
+  pthread_t thread;
+
+  /* Mutex for streams array, must not be held while blocked in poll(2). */
+  pthread_mutex_t mutex;
+
+  /* Sparse array of streams managed by this context. */
+  cubeb_stream * streams[CUBEB_STREAM_MAX];
+
+  /* fds and nfds are only updated by alsa_run when rebuild is set. */
+  struct pollfd * fds;
+  nfds_t nfds;
+  int rebuild;
+
+  int shutdown;
+
+  /* Control pipe for forcing poll to wake and rebuild fds or recalculate the timeout. */
+  int control_fd_read;
+  int control_fd_write;
+
+  /* Track number of active streams.  This is limited to CUBEB_STREAM_MAX
+     due to resource contraints. */
+  unsigned int active_streams;
+
+  /* Local configuration with handle_underrun workaround set for PulseAudio
+     ALSA plugin.  Will be NULL if the PA ALSA plugin is not in use or the
+     workaround is not required. */
+  snd_config_t * local_config;
+  int is_pa;
+};
+
+enum stream_state {
+  INACTIVE,
+  RUNNING,
+  DRAINING,
+  PROCESSING,
+  ERROR
+};
+
+struct cubeb_stream {
+  cubeb * context;
+  pthread_mutex_t mutex;
+  snd_pcm_t * pcm;
+  cubeb_data_callback data_callback;
+  cubeb_state_callback state_callback;
+  void * user_ptr;
+  snd_pcm_uframes_t write_position;
+  snd_pcm_uframes_t last_position;
+  snd_pcm_uframes_t buffer_size;
+  cubeb_stream_params params;
+
+  /* Every member after this comment is protected by the owning context's
+     mutex rather than the stream's mutex, or is only used on the context's
+     run thread. */
+  pthread_cond_t cond; /* Signaled when the stream's state is changed. */
+
+  enum stream_state state;
+
+  struct pollfd * saved_fds; /* A copy of the pollfds passed in at init time. */
+  struct pollfd * fds; /* Pointer to this waitable's pollfds within struct cubeb's fds. */
+  nfds_t nfds;
+
+  struct timeval drain_timeout;
+
+  /* XXX: Horrible hack -- if an active stream has been idle for
+     CUBEB_WATCHDOG_MS it will be disabled and the error callback will be
+     called.  This works around a bug seen with older versions of ALSA and
+     PulseAudio where streams would stop requesting new data despite still
+     being logically active and playing. */
+  struct timeval last_activity;
+  float volume;
+};
+
+static int
+any_revents(struct pollfd * fds, nfds_t nfds)
+{
+  nfds_t i;
+
+  for (i = 0; i < nfds; ++i) {
+    if (fds[i].revents) {
+      return 1;
+    }
+  }
+
+  return 0;
+}
+
+static int
+cmp_timeval(struct timeval * a, struct timeval * b)
+{
+  if (a->tv_sec == b->tv_sec) {
+    if (a->tv_usec == b->tv_usec) {
+      return 0;
+    }
+    return a->tv_usec > b->tv_usec ? 1 : -1;
+  }
+  return a->tv_sec > b->tv_sec ? 1 : -1;
+}
+
+static int
+timeval_to_relative_ms(struct timeval * tv)
+{
+  struct timeval now;
+  struct timeval dt;
+  long long t;
+  int r;
+
+  gettimeofday(&now, NULL);
+  r = cmp_timeval(tv, &now);
+  if (r >= 0) {
+    timersub(tv, &now, &dt);
+  } else {
+    timersub(&now, tv, &dt);
+  }
+  t = dt.tv_sec;
+  t *= 1000;
+  t += (dt.tv_usec + 500) / 1000;
+
+  if (t > INT_MAX) {
+    t = INT_MAX;
+  } else if (t < INT_MIN) {
+    t = INT_MIN;
+  }
+
+  return r >= 0 ? t : -t;
+}
+
+static int
+ms_until(struct timeval * tv)
+{
+  return timeval_to_relative_ms(tv);
+}
+
+static int
+ms_since(struct timeval * tv)
+{
+  return -timeval_to_relative_ms(tv);
+}
+
+static void
+rebuild(cubeb * ctx)
+{
+  nfds_t nfds;
+  int i;
+  nfds_t j;
+  cubeb_stream * stm;
+
+  assert(ctx->rebuild);
+
+  /* Always count context's control pipe fd. */
+  nfds = 1;
+  for (i = 0; i < CUBEB_STREAM_MAX; ++i) {
+    stm = ctx->streams[i];
+    if (stm) {
+      stm->fds = NULL;
+      if (stm->state == RUNNING) {
+        nfds += stm->nfds;
+      }
+    }
+  }
+
+  free(ctx->fds);
+  ctx->fds = calloc(nfds, sizeof(struct pollfd));
+  assert(ctx->fds);
+  ctx->nfds = nfds;
+
+  /* Include context's control pipe fd. */
+  ctx->fds[0].fd = ctx->control_fd_read;
+  ctx->fds[0].events = POLLIN | POLLERR;
+
+  for (i = 0, j = 1; i < CUBEB_STREAM_MAX; ++i) {
+    stm = ctx->streams[i];
+    if (stm && stm->state == RUNNING) {
+      memcpy(&ctx->fds[j], stm->saved_fds, stm->nfds * sizeof(struct pollfd));
+      stm->fds = &ctx->fds[j];
+      j += stm->nfds;
+    }
+  }
+
+  ctx->rebuild = 0;
+}
+
+static void
+poll_wake(cubeb * ctx)
+{
+  if (write(ctx->control_fd_write, "x", 1) < 0) {
+    /* ignore write error */
+  }
+}
+
+static void
+set_timeout(struct timeval * timeout, unsigned int ms)
+{
+  gettimeofday(timeout, NULL);
+  timeout->tv_sec += ms / 1000;
+  timeout->tv_usec += (ms % 1000) * 1000;
+}
+
+static void
+alsa_set_stream_state(cubeb_stream * stm, enum stream_state state)
+{
+  cubeb * ctx;
+  int r;
+
+  ctx = stm->context;
+  stm->state = state;
+  r = pthread_cond_broadcast(&stm->cond);
+  assert(r == 0);
+  ctx->rebuild = 1;
+  poll_wake(ctx);
+}
+
+static enum stream_state
+alsa_refill_stream(cubeb_stream * stm)
+{
+  snd_pcm_sframes_t avail;
+  long got;
+  void * p;
+  int draining;
+
+  draining = 0;
+
+  pthread_mutex_lock(&stm->mutex);
+
+  avail = snd_pcm_avail_update(stm->pcm);
+  if (avail < 0) {
+    snd_pcm_recover(stm->pcm, avail, 1);
+    avail = snd_pcm_avail_update(stm->pcm);
+  }
+
+  /* Failed to recover from an xrun, this stream must be broken. */
+  if (avail < 0) {
+    pthread_mutex_unlock(&stm->mutex);
+    stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_ERROR);
+    return ERROR;
+  }
+
+  /* This should never happen. */
+  if ((unsigned int) avail > stm->buffer_size) {
+    avail = stm->buffer_size;
+  }
+
+  /* poll(2) claims this stream is active, so there should be some space
+     available to write.  If avail is still zero here, the stream must be in
+     a funky state, bail and wait for another wakeup. */
+  if (avail == 0) {
+    pthread_mutex_unlock(&stm->mutex);
+    return RUNNING;
+  }
+
+  p = calloc(1, snd_pcm_frames_to_bytes(stm->pcm, avail));
+  assert(p);
+
+  pthread_mutex_unlock(&stm->mutex);
+  got = stm->data_callback(stm, stm->user_ptr, NULL, p, avail);
+  pthread_mutex_lock(&stm->mutex);
+  if (got < 0) {
+    pthread_mutex_unlock(&stm->mutex);
+    stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_ERROR);
+    free(p);
+    return ERROR;
+  }
+  if (got > 0) {
+    snd_pcm_sframes_t wrote;
+
+    if (stm->params.format == CUBEB_SAMPLE_FLOAT32NE) {
+      float * b = (float *) p;
+      for (uint32_t i = 0; i < got * stm->params.channels; i++) {
+        b[i] *= stm->volume;
+      }
+    } else {
+      short * b = (short *) p;
+      for (uint32_t i = 0; i < got * stm->params.channels; i++) {
+        b[i] *= stm->volume;
+      }
+    }
+    wrote = snd_pcm_writei(stm->pcm, p, got);
+    if (wrote < 0) {
+      snd_pcm_recover(stm->pcm, wrote, 1);
+      wrote = snd_pcm_writei(stm->pcm, p, got);
+    }
+    assert(wrote >= 0 && wrote == got);
+    stm->write_position += wrote;
+    gettimeofday(&stm->last_activity, NULL);
+  }
+  if (got != avail) {
+    long buffer_fill = stm->buffer_size - (avail - got);
+    double buffer_time = (double) buffer_fill / stm->params.rate;
+
+    /* Fill the remaining buffer with silence to guarantee one full period
+       has been written. */
+    snd_pcm_writei(stm->pcm, (char *) p + got, avail - got);
+
+    set_timeout(&stm->drain_timeout, buffer_time * 1000);
+
+    draining = 1;
+  }
+
+  free(p);
+  pthread_mutex_unlock(&stm->mutex);
+  return draining ? DRAINING : RUNNING;
+}
+
+static int
+alsa_run(cubeb * ctx)
+{
+  int r;
+  int timeout;
+  int i;
+  char dummy;
+  cubeb_stream * stm;
+  enum stream_state state;
+
+  pthread_mutex_lock(&ctx->mutex);
+
+  if (ctx->rebuild) {
+    rebuild(ctx);
+  }
+
+  /* Wake up at least once per second for the watchdog. */
+  timeout = 1000;
+  for (i = 0; i < CUBEB_STREAM_MAX; ++i) {
+    stm = ctx->streams[i];
+    if (stm && stm->state == DRAINING) {
+      r = ms_until(&stm->drain_timeout);
+      if (r >= 0 && timeout > r) {
+        timeout = r;
+      }
+    }
+  }
+
+  pthread_mutex_unlock(&ctx->mutex);
+  r = poll(ctx->fds, ctx->nfds, timeout);
+  pthread_mutex_lock(&ctx->mutex);
+
+  if (r > 0) {
+    if (ctx->fds[0].revents & POLLIN) {
+      if (read(ctx->control_fd_read, &dummy, 1) < 0) {
+        /* ignore read error */
+      }
+
+      if (ctx->shutdown) {
+        pthread_mutex_unlock(&ctx->mutex);
+        return -1;
+      }
+    }
+
+    for (i = 0; i < CUBEB_STREAM_MAX; ++i) {
+      stm = ctx->streams[i];
+      /* We can't use snd_pcm_poll_descriptors_revents here because of
+         https://github.com/kinetiknz/cubeb/issues/135. */
+      if (stm && stm->state == RUNNING && stm->fds && any_revents(stm->fds, stm->nfds)) {
+        alsa_set_stream_state(stm, PROCESSING);
+        pthread_mutex_unlock(&ctx->mutex);
+        state = alsa_refill_stream(stm);
+        pthread_mutex_lock(&ctx->mutex);
+        alsa_set_stream_state(stm, state);
+      }
+    }
+  } else if (r == 0) {
+    for (i = 0; i < CUBEB_STREAM_MAX; ++i) {
+      stm = ctx->streams[i];
+      if (stm) {
+        if (stm->state == DRAINING && ms_since(&stm->drain_timeout) >= 0) {
+          alsa_set_stream_state(stm, INACTIVE);
+          stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_DRAINED);
+        } else if (stm->state == RUNNING && ms_since(&stm->last_activity) > CUBEB_WATCHDOG_MS) {
+          alsa_set_stream_state(stm, ERROR);
+          stm->state_callback(stm, stm->user_ptr, CUBEB_STATE_ERROR);
+        }
+      }
+    }
+  }
+
+  pthread_mutex_unlock(&ctx->mutex);
+
+  return 0;
+}
+
+static void *
+alsa_run_thread(void * context)
+{
+  cubeb * ctx = context;
+  int r;
+
+  do {
+    r = alsa_run(ctx);
+  } while (r >= 0);
+
+  return NULL;
+}
+
+static snd_config_t *
+get_slave_pcm_node(snd_config_t * lconf, snd_config_t * root_pcm)
+{
+  int r;
+  snd_config_t * slave_pcm;
+  snd_config_t * slave_def;
+  snd_config_t * pcm;
+  char const * string;
+  char node_name[64];
+
+  slave_def = NULL;
+
+  r = snd_config_search(root_pcm, "slave", &slave_pcm);
+  if (r < 0) {
+    return NULL;
+  }
+
+  r = snd_config_get_string(slave_pcm, &string);
+  if (r >= 0) {
+    r = snd_config_search_definition(lconf, "pcm_slave", string, &slave_def);
+    if (r < 0) {
+      return NULL;
+    }
+  }
+
+  do {
+    r = snd_config_search(slave_def ? slave_def : slave_pcm, "pcm", &pcm);
+    if (r < 0) {
+      break;
+    }
+
+    r = snd_config_get_string(slave_def ? slave_def : slave_pcm, &string);
+    if (r < 0) {
+      break;
+    }
+
+    r = snprintf(node_name, sizeof(node_name), "pcm.%s", string);
+    if (r < 0 || r > (int) sizeof(node_name)) {
+      break;
+    }
+    r = snd_config_search(lconf, node_name, &pcm);
+    if (r < 0) {
+      break;
+    }
+
+    return pcm;
+  } while (0);
+
+  if (slave_def) {
+    snd_config_delete(slave_def);
+  }
+
+  return NULL;
+}
+
+/* Work around PulseAudio ALSA plugin bug where the PA server forces a
+   higher than requested latency, but the plugin does not update its (and
+   ALSA's) internal state to reflect that, leading to an immediate underrun
+   situation.  Inspired by WINE's make_handle_underrun_config.
+   Reference: http://mailman.alsa-project.org/pipermail/alsa-devel/2012-July/05 */
+static snd_config_t *
+init_local_config_with_workaround(char const * pcm_name)
+{
+  int r;
+  snd_config_t * lconf;
+  snd_config_t * pcm_node;
+  snd_config_t * node;
+  char const * string;
+  char node_name[64];
+
+  lconf = NULL;
+
+  if (snd_config == NULL) {
+    return NULL;
+  }
+
+  r = snd_config_copy(&lconf, snd_config);
+  if (r < 0) {
+    return NULL;
+  }
+
+  do {
+    r = snd_config_search_definition(lconf, "pcm", pcm_name, &pcm_node);
+    if (r < 0) {
+      break;
+    }
+
+    r = snd_config_get_id(pcm_node, &string);
+    if (r < 0) {
+      break;
+    }
+
+    r = snprintf(node_name, sizeof(node_name), "pcm.%s", string);
+    if (r < 0 || r > (int) sizeof(node_name)) {
+      break;
+    }
+    r = snd_config_search(lconf, node_name, &pcm_node);
+    if (r < 0) {
+      break;
+    }
+
+    /* If this PCM has a slave, walk the slave configurations until we reach the bottom. */
+    while ((node = get_slave_pcm_node(lconf, pcm_node)) != NULL) {
+      pcm_node = node;
+    }
+
+    /* Fetch the PCM node's type, and bail out if it's not the PulseAudio plugin. */
+    r = snd_config_search(pcm_node, "type", &node);
+    if (r < 0) {
+      break;
+    }
+
+    r = snd_config_get_string(node, &string);
+    if (r < 0) {
+      break;
+    }
+
+    if (strcmp(string, "pulse") != 0) {
+      break;
+    }
+
+    /* Don't clobber an explicit existing handle_underrun value, set it only
+       if it doesn't already exist. */
+    r = snd_config_search(pcm_node, "handle_underrun", &node);
+    if (r != -ENOENT) {
+      break;
+    }
+
+    /* Disable pcm_pulse's asynchronous underrun handling. */
+    r = snd_config_imake_integer(&node, "handle_underrun", 0);
+    if (r < 0) {
+      break;
+    }
+
+    r = snd_config_add(pcm_node, node);
+    if (r < 0) {
+      break;
+    }
+
+    return lconf;
+  } while (0);
+
+  snd_config_delete(lconf);
+
+  return NULL;
+}
+
+static int
+alsa_locked_pcm_open(snd_pcm_t ** pcm, snd_pcm_stream_t stream, snd_config_t * local_config)
+{
+  int r;
+
+  pthread_mutex_lock(&cubeb_alsa_mutex);
+  if (local_config) {
+    r = snd_pcm_open_lconf(pcm, CUBEB_ALSA_PCM_NAME, stream, SND_PCM_NONBLOCK, local_config);
+  } else {
+    r = snd_pcm_open(pcm, CUBEB_ALSA_PCM_NAME, stream, SND_PCM_NONBLOCK);
+  }
+  pthread_mutex_unlock(&cubeb_alsa_mutex);
+
+  return r;
+}
+
+static int
+alsa_locked_pcm_close(snd_pcm_t * pcm)
+{
+  int r;
+
+  pthread_mutex_lock(&cubeb_alsa_mutex);
+  r = snd_pcm_close(pcm);
+  pthread_mutex_unlock(&cubeb_alsa_mutex);
+
+  return r;
+}
+
+static int
+alsa_register_stream(cubeb * ctx, cubeb_stream * stm)
+{
+  int i;
+
+  pthread_mutex_lock(&ctx->mutex);
+  for (i = 0; i < CUBEB_STREAM_MAX; ++i) {
+    if (!ctx->streams[i]) {
+      ctx->streams[i] = stm;
+      break;
+    }
+  }
+  pthread_mutex_unlock(&ctx->mutex);
+
+  return i == CUBEB_STREAM_MAX;
+}
+
+static void
+alsa_unregister_stream(cubeb_stream * stm)
+{
+  cubeb * ctx;
+  int i;
+
+  ctx = stm->context;
+
+  pthread_mutex_lock(&ctx->mutex);
+  for (i = 0; i < CUBEB_STREAM_MAX; ++i) {
+    if (ctx->streams[i] == stm) {
+      ctx->streams[i] = NULL;
+      break;
+    }
+  }
+  pthread_mutex_unlock(&ctx->mutex);
+}
+
+static void
+silent_error_handler(char const * file, int line, char const * function,
+                     int err, char const * fmt, ...)
+{
+  (void)file;
+  (void)line;
+  (void)function;
+  (void)err;
+  (void)fmt;
+}
+
+/*static*/ int
+alsa_init(cubeb ** context, char const * context_name)
+{
+  (void)context_name;
+  cubeb * ctx;
+  int r;
+  int i;
+  int fd[2];
+  pthread_attr_t attr;
+  snd_pcm_t * dummy;
+
+  assert(context);
+  *context = NULL;
+
+  pthread_mutex_lock(&cubeb_alsa_mutex);
+  if (!cubeb_alsa_error_handler_set) {
+    snd_lib_error_set_handler(silent_error_handler);
+    cubeb_alsa_error_handler_set = 1;
+  }
+  pthread_mutex_unlock(&cubeb_alsa_mutex);
+
+  ctx = calloc(1, sizeof(*ctx));
+  assert(ctx);
+
+  ctx->ops = &alsa_ops;
+
+  r = pthread_mutex_init(&ctx->mutex, NULL);
+  assert(r == 0);
+
+  r = pipe(fd);
+  assert(r == 0);
+
+  for (i = 0; i < 2; ++i) {
+    fcntl(fd[i], F_SETFD, fcntl(fd[i], F_GETFD) | FD_CLOEXEC);
+    fcntl(fd[i], F_SETFL, fcntl(fd[i], F_GETFL) | O_NONBLOCK);
+  }
+
+  ctx->control_fd_read = fd[0];
+  ctx->control_fd_write = fd[1];
+
+  /* Force an early rebuild when alsa_run is first called to ensure fds and
+     nfds have been initialized. */
+  ctx->rebuild = 1;
+
+  r = pthread_attr_init(&attr);
+  assert(r == 0);
+
+  r = pthread_attr_setstacksize(&attr, 256 * 1024);
+  assert(r == 0);
+
+  r = pthread_create(&ctx->thread, &attr, alsa_run_thread, ctx);
+  assert(r == 0);
+
+  r = pthread_attr_destroy(&attr);
+  assert(r == 0);
+
+  /* Open a dummy PCM to force the configuration space to be evaluated so that
+     init_local_config_with_workaround can find and modify the default node. */
+  r = alsa_locked_pcm_open(&dummy, SND_PCM_STREAM_PLAYBACK, NULL);
+  if (r >= 0) {
+    alsa_locked_pcm_close(dummy);
+  }
+  ctx->is_pa = 0;
+  pthread_mutex_lock(&cubeb_alsa_mutex);
+  ctx->local_config = init_local_config_with_workaround(CUBEB_ALSA_PCM_NAME);
+  pthread_mutex_unlock(&cubeb_alsa_mutex);
+  if (ctx->local_config) {
+    ctx->is_pa = 1;
+    r = alsa_locked_pcm_open(&dummy, SND_PCM_STREAM_PLAYBACK, ctx->local_config);
+    /* If we got a local_config, we found a PA PCM.  If opening a PCM with that
+       config fails with EINVAL, the PA PCM is too old for this workaround. */
+    if (r == -EINVAL) {
+      pthread_mutex_lock(&cubeb_alsa_mutex);
+      snd_config_delete(ctx->local_config);
+      pthread_mutex_unlock(&cubeb_alsa_mutex);
+      ctx->local_config = NULL;
+    } else if (r >= 0) {
+      alsa_locked_pcm_close(dummy);
+    }
+  }
+
+  *context = ctx;
+
+  return CUBEB_OK;
+}
+
+static char const *
+alsa_get_backend_id(cubeb * ctx)
+{
+  (void)ctx;
+  return "alsa";
+}
+
+static void
+alsa_destroy(cubeb * ctx)
+{
+  int r;
+
+  assert(ctx);
+
+  pthread_mutex_lock(&ctx->mutex);
+  ctx->shutdown = 1;
+  poll_wake(ctx);
+  pthread_mutex_unlock(&ctx->mutex);
+
+  r = pthread_join(ctx->thread, NULL);
+  assert(r == 0);
+
+  close(ctx->control_fd_read);
+  close(ctx->control_fd_write);
+  pthread_mutex_destroy(&ctx->mutex);
+  free(ctx->fds);
+
+  if (ctx->local_config) {
+    pthread_mutex_lock(&cubeb_alsa_mutex);
+    snd_config_delete(ctx->local_config);
+    pthread_mutex_unlock(&cubeb_alsa_mutex);
+  }
+
+  free(ctx);
+}
+
+static void alsa_stream_destroy(cubeb_stream * stm);
+
+static int
+alsa_stream_init(cubeb * ctx, cubeb_stream ** stream, char const * stream_name,
+                 cubeb_devid input_device,
+                 cubeb_stream_params * input_stream_params,
+                 cubeb_devid output_device,
+                 cubeb_stream_params * output_stream_params,
+                 unsigned int latency_frames,
+                 cubeb_data_callback data_callback, cubeb_state_callback state_callback,
+                 void * user_ptr)
+{
+  (void)stream_name;
+  cubeb_stream * stm;
+  int r;
+  snd_pcm_format_t format;
+  snd_pcm_uframes_t period_size;
+  int latency_us = 0;
+
+
+  assert(ctx && stream);
+
+  if (input_stream_params) {
+    /* Capture support not yet implemented. */
+    return CUBEB_ERROR_NOT_SUPPORTED;
+  }
+
+  if (input_device || output_device) {
+    /* Device selection not yet implemented. */
+    return CUBEB_ERROR_DEVICE_UNAVAILABLE;
+  }
+
+  *stream = NULL;
+
+  switch (output_stream_params->format) {
+  case CUBEB_SAMPLE_S16LE:
+    format = SND_PCM_FORMAT_S16_LE;
+    break;
+  case CUBEB_SAMPLE_S16BE:
+    format = SND_PCM_FORMAT_S16_BE;
+    break;
+  case CUBEB_SAMPLE_FLOAT32LE:
+    format = SND_PCM_FORMAT_FLOAT_LE;
+    break;
+  case CUBEB_SAMPLE_FLOAT32BE:
+    format = SND_PCM_FORMAT_FLOAT_BE;
+    break;
+  default:
+    return CUBEB_ERROR_INVALID_FORMAT;
+  }
+
+  pthread_mutex_lock(&ctx->mutex);
+  if (ctx->active_streams >= CUBEB_STREAM_MAX) {
+    pthread_mutex_unlock(&ctx->mutex);
+    return CUBEB_ERROR;
+  }
+  ctx->active_streams += 1;
+  pthread_mutex_unlock(&ctx->mutex);
+
+  stm = calloc(1, sizeof(*stm));
+  assert(stm);
+
+  stm->context = ctx;
+  stm->data_callback = data_callback;
+  stm->state_callback = state_callback;
+  stm->user_ptr = user_ptr;
+  stm->params = *output_stream_params;
+  stm->state = INACTIVE;
+  stm->volume = 1.0;
+
+  r = pthread_mutex_init(&stm->mutex, NULL);
+  assert(r == 0);
+
+  r = alsa_locked_pcm_open(&stm->pcm, SND_PCM_STREAM_PLAYBACK, ctx->local_config);
+  if (r < 0) {
+    alsa_stream_destroy(stm);
+    return CUBEB_ERROR;
+  }
+
+  r = snd_pcm_nonblock(stm->pcm, 1);
+  assert(r == 0);
+
+  latency_us = latency_frames * 1e6 / stm->params.rate;
+
+  /* Ugly hack: the PA ALSA plugin allows buffer configurations that can't
+     possibly work.  See https://bugzilla.mozilla.org/show_bug.cgi?id=761274.
+     Only resort to this hack if the handle_underrun workaround failed. */
+  if (!ctx->local_config && ctx->is_pa) {
+    const int min_latency = 5e5;
+    latency_us = latency_us < min_latency ? min_latency: latency_us;
+  }
+
+  r = snd_pcm_set_params(stm->pcm, format, SND_PCM_ACCESS_RW_INTERLEAVED,
+                         stm->params.channels, stm->params.rate, 1,
+                         latency_us);
+  if (r < 0) {
+    alsa_stream_destroy(stm);
+    return CUBEB_ERROR_INVALID_FORMAT;
+  }
+
+  r = snd_pcm_get_params(stm->pcm, &stm->buffer_size, &period_size);
+  assert(r == 0);
+
+  stm->nfds = snd_pcm_poll_descriptors_count(stm->pcm);
+  assert(stm->nfds > 0);
+
+  stm->saved_fds = calloc(stm->nfds, sizeof(struct pollfd));
+  assert(stm->saved_fds);
+  r = snd_pcm_poll_descriptors(stm->pcm, stm->saved_fds, stm->nfds);
+  assert((nfds_t) r == stm->nfds);
+
+  r = pthread_cond_init(&stm->cond, NULL);
+  assert(r == 0);
+
+  if (alsa_register_stream(ctx, stm) != 0) {
+    alsa_stream_destroy(stm);
+    return CUBEB_ERROR;
+  }
+
+  *stream = stm;
+
+  return CUBEB_OK;
+}
+
+static void
+alsa_stream_destroy(cubeb_stream * stm)
+{
+  int r;
+  cubeb * ctx;
+
+  assert(stm && (stm->state == INACTIVE ||
+                 stm->state == ERROR ||
+                 stm->state == DRAINING));
+
+  ctx = stm->context;
+
+  pthread_mutex_lock(&stm->mutex);
+  if (stm->pcm) {
+    if (stm->state == DRAINING) {
+      snd_pcm_drain(stm->pcm);
+    }
+    alsa_locked_pcm_close(stm->pcm);
+    stm->pcm = NULL;
+  }
+  free(stm->saved_fds);
+  pthread_mutex_unlock(&stm->mutex);
+  pthread_mutex_destroy(&stm->mutex);
+
+  r = pthread_cond_destroy(&stm->cond);
+  assert(r == 0);
+
+  alsa_unregister_stream(stm);
+
+  pthread_mutex_lock(&ctx->mutex);
+  assert(ctx->active_streams >= 1);
+  ctx->active_streams -= 1;
+  pthread_mutex_unlock(&ctx->mutex);
+
+  free(stm);
+}
+
+static int
+alsa_get_max_channel_count(cubeb * ctx, uint32_t * max_channels)
+{
+  int r;
+  cubeb_stream * stm;
+  snd_pcm_hw_params_t* hw_params;
+  cubeb_stream_params params;
+  params.rate = 44100;
+  params.format = CUBEB_SAMPLE_FLOAT32NE;
+  params.channels = 2;
+
+  snd_pcm_hw_params_alloca(&hw_params);
+
+  assert(ctx);
+
+  r = alsa_stream_init(ctx, &stm, "", NULL, NULL, NULL, &params, 100, NULL, NULL, NULL);
+  if (r != CUBEB_OK) {
+    return CUBEB_ERROR;
+  }
+
+  r = snd_pcm_hw_params_any(stm->pcm, hw_params);
+  if (r < 0) {
+    return CUBEB_ERROR;
+  }
+
+  r = snd_pcm_hw_params_get_channels_max(hw_params, max_channels);
+  if (r < 0) {
+    return CUBEB_ERROR;
+  }
+
+  alsa_stream_destroy(stm);
+
+  return CUBEB_OK;
+}
+
+static int
+alsa_get_preferred_sample_rate(cubeb * ctx, uint32_t * rate) {
+  (void)ctx;
+  int r, dir;
+  snd_pcm_t * pcm;
+  snd_pcm_hw_params_t * hw_params;
+
+  snd_pcm_hw_params_alloca(&hw_params);
+
+  /* get a pcm, disabling resampling, so we get a rate the
+   * hardware/dmix/pulse/etc. supports. */
+  r = snd_pcm_open(&pcm, CUBEB_ALSA_PCM_NAME, SND_PCM_STREAM_PLAYBACK, SND_PCM_NO_AUTO_RESAMPLE);
+  if (r < 0) {
+    return CUBEB_ERROR;
+  }
+
+  r = snd_pcm_hw_params_any(pcm, hw_params);
+  if (r < 0) {
+    snd_pcm_close(pcm);
+    return CUBEB_ERROR;
+  }
+
+  r = snd_pcm_hw_params_get_rate(hw_params, rate, &dir);
+  if (r >= 0) {
+    /* There is a default rate: use it. */
+    snd_pcm_close(pcm);
+    return CUBEB_OK;
+  }
+
+  /* Use a common rate, alsa may adjust it based on hw/etc. capabilities. */
+  *rate = 44100;
+
+  r = snd_pcm_hw_params_set_rate_near(pcm, hw_params, rate, NULL);
+  if (r < 0) {
+    snd_pcm_close(pcm);
+    return CUBEB_ERROR;
+  }
+
+  snd_pcm_close(pcm);
+
+  return CUBEB_OK;
+}
+
+static int
+alsa_get_min_latency(cubeb * ctx, cubeb_stream_params params, uint32_t * latency_frames)
+{
+  (void)ctx;
+  /* 40ms is found to be an acceptable minimum, even on a super low-end
+   * machine. */
+  *latency_frames = 40 * params.rate / 1000;
+
+  return CUBEB_OK;
+}
+
+static int
+alsa_stream_start(cubeb_stream * stm)
+{
+  cubeb * ctx;
+
+  assert(stm);
+  ctx = stm->context;
+
+  pthread_mutex_lock(&stm->mutex);
+  snd_pcm_pause(stm->pcm, 0);
+  gettimeofday(&stm->last_activity, NULL);
+  pthread_mutex_unlock(&stm->mutex);
+
+  pthread_mutex_lock(&ctx->mutex);
+  if (stm->state != INACTIVE) {
+    pthread_mutex_unlock(&ctx->mutex);
+    return CUBEB_ERROR;
+  }
+  alsa_set_stream_state(stm, RUNNING);
+  pthread_mutex_unlock(&ctx->mutex);
+
+  return CUBEB_OK;
+}
+
+static int
+alsa_stream_stop(cubeb_stream * stm)
+{
+  cubeb * ctx;
+  int r;
+
+  assert(stm);
+  ctx = stm->context;
+
+  pthread_mutex_lock(&ctx->mutex);
+  while (stm->state == PROCESSING) {
+    r = pthread_cond_wait(&stm->cond, &ctx->mutex);
+    assert(r == 0);
+  }
+
+  alsa_set_stream_state(stm, INACTIVE);
+  pthread_mutex_unlock(&ctx->mutex);
+
+  pthread_mutex_lock(&stm->mutex);
+  snd_pcm_pause(stm->pcm, 1);
+  pthread_mutex_unlock(&stm->mutex);
+
+  return CUBEB_OK;
+}
+
+static int
+alsa_stream_get_position(cubeb_stream * stm, uint64_t * position)
+{
+  snd_pcm_sframes_t delay;
+
+  assert(stm && position);
+
+  pthread_mutex_lock(&stm->mutex);
+
+  delay = -1;
+  if (snd_pcm_state(stm->pcm) != SND_PCM_STATE_RUNNING ||
+      snd_pcm_delay(stm->pcm, &delay) != 0) {
+    *position = stm->last_position;
+    pthread_mutex_unlock(&stm->mutex);
+    return CUBEB_OK;
+  }
+
+  assert(delay >= 0);
+
+  *position = 0;
+  if (stm->write_position >= (snd_pcm_uframes_t) delay) {
+    *position = stm->write_position - delay;
+  }
+
+  stm->last_position = *position;
+
+  pthread_mutex_unlock(&stm->mutex);
+  return CUBEB_OK;
+}
+
+static int
+alsa_stream_get_latency(cubeb_stream * stm, uint32_t * latency)
+{
+  snd_pcm_sframes_t delay;
+  /* This function returns the delay in frames until a frame written using
+     snd_pcm_writei is sent to the DAC. The DAC delay should be < 1ms anyways. */
+  if (snd_pcm_delay(stm->pcm, &delay)) {
+    return CUBEB_ERROR;
+  }
+
+  *latency = delay;
+
+  return CUBEB_OK;
+}
+
+static int
+alsa_stream_set_volume(cubeb_stream * stm, float volume)
+{
+  /* setting the volume using an API call does not seem very stable/supported */
+  pthread_mutex_lock(&stm->mutex);
+  stm->volume = volume;
+  pthread_mutex_unlock(&stm->mutex);
+
+  return CUBEB_OK;
+}
+
+static struct cubeb_ops const alsa_ops = {
+  .init = alsa_init,
+  .get_backend_id = alsa_get_backend_id,
+  .get_max_channel_count = alsa_get_max_channel_count,
+  .get_min_latency = alsa_get_min_latency,
+  .get_preferred_sample_rate = alsa_get_preferred_sample_rate,
+  .enumerate_devices = NULL,
+  .destroy = alsa_destroy,
+  .stream_init = alsa_stream_init,
+  .stream_destroy = alsa_stream_destroy,
+  .stream_start = alsa_stream_start,
+  .stream_stop = alsa_stream_stop,
+  .stream_get_position = alsa_stream_get_position,
+  .stream_get_latency = alsa_stream_get_latency,
+  .stream_set_volume = alsa_stream_set_volume,
+  .stream_set_panning = NULL,
+  .stream_get_current_device = NULL,
+  .stream_device_destroy = NULL,
+  .stream_register_device_changed_callback = NULL,
+  .register_device_collection_changed = NULL
+};