tor-browser

cubeb_alsa.c (40461B)

---

/*
* 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
#if defined(__NetBSD__)
#define _NETBSD_SOURCE /* timersub() */
#endif
#define _XOPEN_SOURCE 500
#include "cubeb-internal.h"
#include "cubeb/cubeb.h"
#include "cubeb_tracing.h"
#include <alsa/asoundlib.h>
#include <assert.h>
#include <dlfcn.h>
#include <limits.h>
#include <poll.h>
#include <pthread.h>
#include <sys/time.h>
#include <unistd.h>

#ifdef DISABLE_LIBASOUND_DLOPEN
#define WRAP(x) x
#else
#define WRAP(x) (*cubeb_##x)
#define LIBASOUND_API_VISIT(X)                                                 \
 X(snd_config)                                                                \
 X(snd_config_add)                                                            \
 X(snd_config_copy)                                                           \
 X(snd_config_delete)                                                         \
 X(snd_config_get_id)                                                         \
 X(snd_config_get_string)                                                     \
 X(snd_config_imake_integer)                                                  \
 X(snd_config_search)                                                         \
 X(snd_config_search_definition)                                              \
 X(snd_lib_error_set_handler)                                                 \
 X(snd_pcm_avail_update)                                                      \
 X(snd_pcm_close)                                                             \
 X(snd_pcm_delay)                                                             \
 X(snd_pcm_drain)                                                             \
 X(snd_pcm_frames_to_bytes)                                                   \
 X(snd_pcm_get_params)                                                        \
 X(snd_pcm_hw_params_any)                                                     \
 X(snd_pcm_hw_params_get_channels_max)                                        \
 X(snd_pcm_hw_params_get_rate)                                                \
 X(snd_pcm_hw_params_set_rate_near)                                           \
 X(snd_pcm_hw_params_sizeof)                                                  \
 X(snd_pcm_nonblock)                                                          \
 X(snd_pcm_open)                                                              \
 X(snd_pcm_open_lconf)                                                        \
 X(snd_pcm_pause)                                                             \
 X(snd_pcm_poll_descriptors)                                                  \
 X(snd_pcm_poll_descriptors_count)                                            \
 X(snd_pcm_poll_descriptors_revents)                                          \
 X(snd_pcm_readi)                                                             \
 X(snd_pcm_recover)                                                           \
 X(snd_pcm_set_params)                                                        \
 X(snd_pcm_start)                                                             \
 X(snd_pcm_state)                                                             \
 X(snd_pcm_writei)

#define MAKE_TYPEDEF(x) static typeof(x) * cubeb_##x;
LIBASOUND_API_VISIT(MAKE_TYPEDEF);
#undef MAKE_TYPEDEF
/* snd_pcm_hw_params_alloca is actually a macro */
#define snd_pcm_hw_params_sizeof cubeb_snd_pcm_hw_params_sizeof
#endif

#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;
 void * libasound;

 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 {
 /* Note: Must match cubeb_stream layout in cubeb.c. */
 cubeb * context;
 void * user_ptr;
 /**/
 pthread_mutex_t mutex;
 snd_pcm_t * pcm;
 cubeb_data_callback data_callback;
 cubeb_state_callback state_callback;
 snd_pcm_uframes_t stream_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;

 char * buffer;
 snd_pcm_uframes_t bufframes;
 snd_pcm_stream_t stream_type;

 struct cubeb_stream * other_stream;
};

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
stream_buffer_decrement(cubeb_stream * stm, long count)
{
 char * bufremains =
     stm->buffer + WRAP(snd_pcm_frames_to_bytes)(stm->pcm, count);
 memmove(stm->buffer, bufremains,
         WRAP(snd_pcm_frames_to_bytes)(stm->pcm, stm->bufframes - count));
 stm->bufframes -= count;
}

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_process_stream(cubeb_stream * stm)
{
 unsigned short revents;
 snd_pcm_sframes_t avail;
 int draining;

 draining = 0;

 pthread_mutex_lock(&stm->mutex);

 /* Call _poll_descriptors_revents() even if we don't use it
    to let underlying plugins clear null events.  Otherwise poll()
    may wake up again and again, producing unnecessary CPU usage. */
 WRAP(snd_pcm_poll_descriptors_revents)
 (stm->pcm, stm->fds, stm->nfds, &revents);

 avail = WRAP(snd_pcm_avail_update)(stm->pcm);

 /* Got null event? Bail and wait for another wakeup. */
 if (avail == 0) {
   pthread_mutex_unlock(&stm->mutex);
   return RUNNING;
 }

 /* This could happen if we were suspended with SIGSTOP/Ctrl+Z for a long time.
  */
 if ((unsigned int)avail > stm->buffer_size) {
   avail = stm->buffer_size;
 }

 /* Capture: Read available frames */
 if (stm->stream_type == SND_PCM_STREAM_CAPTURE && avail > 0) {
   snd_pcm_sframes_t got;

   if (avail + stm->bufframes > stm->buffer_size) {
     /* Buffer overflow. Skip and overwrite with new data. */
     stm->bufframes = 0;
     // TODO: should it be marked as DRAINING?
   }

   got = WRAP(snd_pcm_readi)(stm->pcm, stm->buffer + stm->bufframes, avail);

   if (got < 0) {
     avail = got; // the error handler below will recover us
   } else {
     stm->bufframes += got;
     stm->stream_position += got;

     gettimeofday(&stm->last_activity, NULL);
   }
 }

 /* Capture: Pass read frames to callback function */
 if (stm->stream_type == SND_PCM_STREAM_CAPTURE && stm->bufframes > 0 &&
     (!stm->other_stream ||
      stm->other_stream->bufframes < stm->other_stream->buffer_size)) {
   snd_pcm_sframes_t wrote = stm->bufframes;
   struct cubeb_stream * mainstm = stm->other_stream ? stm->other_stream : stm;
   void * other_buffer = stm->other_stream ? stm->other_stream->buffer +
                                                 stm->other_stream->bufframes
                                           : NULL;

   /* Correct write size to the other stream available space */
   if (stm->other_stream &&
       wrote > (snd_pcm_sframes_t)(stm->other_stream->buffer_size -
                                   stm->other_stream->bufframes)) {
     wrote = stm->other_stream->buffer_size - stm->other_stream->bufframes;
   }

   pthread_mutex_unlock(&stm->mutex);
   wrote = stm->data_callback(mainstm, stm->user_ptr, stm->buffer,
                              other_buffer, wrote);
   pthread_mutex_lock(&stm->mutex);

   if (wrote < 0) {
     avail = wrote; // the error handler below will recover us
   } else {
     stream_buffer_decrement(stm, wrote);

     if (stm->other_stream) {
       stm->other_stream->bufframes += wrote;
     }
   }
 }

 /* Playback: Don't have enough data? Let's ask for more. */
 if (stm->stream_type == SND_PCM_STREAM_PLAYBACK &&
     avail > (snd_pcm_sframes_t)stm->bufframes &&
     (!stm->other_stream || stm->other_stream->bufframes > 0)) {
   long got = avail - stm->bufframes;
   void * other_buffer = stm->other_stream ? stm->other_stream->buffer : NULL;
   char * buftail =
       stm->buffer + WRAP(snd_pcm_frames_to_bytes)(stm->pcm, stm->bufframes);

   /* Correct read size to the other stream available frames */
   if (stm->other_stream &&
       got > (snd_pcm_sframes_t)stm->other_stream->bufframes) {
     got = stm->other_stream->bufframes;
   }

   pthread_mutex_unlock(&stm->mutex);
   got = stm->data_callback(stm, stm->user_ptr, other_buffer, buftail, got);
   pthread_mutex_lock(&stm->mutex);

   if (got < 0) {
     avail = got; // the error handler below will recover us
   } else {
     stm->bufframes += got;

     if (stm->other_stream) {
       stream_buffer_decrement(stm->other_stream, got);
     }
   }
 }

 /* Playback: Still don't have enough data? Add some silence. */
 if (stm->stream_type == SND_PCM_STREAM_PLAYBACK &&
     avail > (snd_pcm_sframes_t)stm->bufframes) {
   long drain_frames = avail - stm->bufframes;
   double drain_time = (double)drain_frames / stm->params.rate;

   char * buftail =
       stm->buffer + WRAP(snd_pcm_frames_to_bytes)(stm->pcm, stm->bufframes);
   memset(buftail, 0, WRAP(snd_pcm_frames_to_bytes)(stm->pcm, drain_frames));
   stm->bufframes = avail;

   /* Mark as draining, unless we're waiting for capture */
   if (!stm->other_stream || stm->other_stream->bufframes > 0) {
     set_timeout(&stm->drain_timeout, drain_time * 1000);

     draining = 1;
   }
 }

 /* Playback: Have enough data and no errors. Let's write it out. */
 if (stm->stream_type == SND_PCM_STREAM_PLAYBACK && avail > 0) {
   snd_pcm_sframes_t wrote;

   if (stm->params.format == CUBEB_SAMPLE_FLOAT32NE) {
     float * b = (float *)stm->buffer;
     for (uint32_t i = 0; i < avail * stm->params.channels; i++) {
       b[i] *= stm->volume;
     }
   } else {
     short * b = (short *)stm->buffer;
     for (uint32_t i = 0; i < avail * stm->params.channels; i++) {
       b[i] *= stm->volume;
     }
   }

   wrote = WRAP(snd_pcm_writei)(stm->pcm, stm->buffer, avail);
   if (wrote < 0) {
     avail = wrote; // the error handler below will recover us
   } else {
     stream_buffer_decrement(stm, wrote);

     stm->stream_position += wrote;
     gettimeofday(&stm->last_activity, NULL);
   }
 }

 /* Got some error? Let's try to recover the stream. */
 if (avail < 0) {
   avail = WRAP(snd_pcm_recover)(stm->pcm, avail, 0);

   /* Capture pcm must be started after initial setup/recover */
   if (avail >= 0 && stm->stream_type == SND_PCM_STREAM_CAPTURE &&
       WRAP(snd_pcm_state)(stm->pcm) == SND_PCM_STATE_PREPARED) {
     avail = WRAP(snd_pcm_start)(stm->pcm);
   }
 }

 /* Failed to recover, 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;
 }

 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_process_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;

 CUBEB_REGISTER_THREAD("cubeb rendering thread");

 do {
   r = alsa_run(ctx);
 } while (r >= 0);

 CUBEB_UNREGISTER_THREAD();

 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 = WRAP(snd_config_search)(root_pcm, "slave", &slave_pcm);
 if (r < 0) {
   return NULL;
 }

 r = WRAP(snd_config_get_string)(slave_pcm, &string);
 if (r >= 0) {
   r = WRAP(snd_config_search_definition)(lconf, "pcm_slave", string,
                                          &slave_def);
   if (r < 0) {
     return NULL;
   }
 }

 do {
   r = WRAP(snd_config_search)(slave_def ? slave_def : slave_pcm, "pcm", &pcm);
   if (r < 0) {
     break;
   }

   r = WRAP(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 = WRAP(snd_config_search)(lconf, node_name, &pcm);
   if (r < 0) {
     break;
   }

   return pcm;
 } while (0);

 if (slave_def) {
   WRAP(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 (WRAP(snd_config) == NULL) {
   return NULL;
 }

 r = WRAP(snd_config_copy)(&lconf, WRAP(snd_config));
 if (r < 0) {
   return NULL;
 }

 do {
   r = WRAP(snd_config_search_definition)(lconf, "pcm", pcm_name, &pcm_node);
   if (r < 0) {
     break;
   }

   r = WRAP(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 = WRAP(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 = WRAP(snd_config_search)(pcm_node, "type", &node);
   if (r < 0) {
     break;
   }

   r = WRAP(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 = WRAP(snd_config_search)(pcm_node, "handle_underrun", &node);
   if (r != -ENOENT) {
     break;
   }

   /* Disable pcm_pulse's asynchronous underrun handling. */
   r = WRAP(snd_config_imake_integer)(&node, "handle_underrun", 0);
   if (r < 0) {
     break;
   }

   r = WRAP(snd_config_add)(pcm_node, node);
   if (r < 0) {
     break;
   }

   return lconf;
 } while (0);

 WRAP(snd_config_delete)(lconf);

 return NULL;
}

static int
alsa_locked_pcm_open(snd_pcm_t ** pcm, char const * pcm_name,
                    snd_pcm_stream_t stream, snd_config_t * local_config)
{
 int r;

 pthread_mutex_lock(&cubeb_alsa_mutex);
 if (local_config) {
   r = WRAP(snd_pcm_open_lconf)(pcm, pcm_name, stream, SND_PCM_NONBLOCK,
                                local_config);
 } else {
   r = WRAP(snd_pcm_open)(pcm, 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 = WRAP(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;
 void * libasound = NULL;
 cubeb * ctx;
 int r;
 int i;
 int fd[2];
 pthread_attr_t attr;
 snd_pcm_t * dummy;

 assert(context);
 *context = NULL;

#ifndef DISABLE_LIBASOUND_DLOPEN
 libasound = dlopen("libasound.so.2", RTLD_LAZY);
 if (!libasound) {
   libasound = dlopen("libasound.so", RTLD_LAZY);
   if (!libasound) {
     return CUBEB_ERROR;
   }
 }

#define LOAD(x)                                                                \
 {                                                                            \
   cubeb_##x = dlsym(libasound, #x);                                          \
   if (!cubeb_##x) {                                                          \
     dlclose(libasound);                                                      \
     return CUBEB_ERROR;                                                      \
   }                                                                          \
 }

 LIBASOUND_API_VISIT(LOAD);
#undef LOAD
#endif

 pthread_mutex_lock(&cubeb_alsa_mutex);
 if (!cubeb_alsa_error_handler_set) {
   WRAP(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;
 ctx->libasound = libasound;

 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, CUBEB_ALSA_PCM_NAME, 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, CUBEB_ALSA_PCM_NAME,
                            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);
     WRAP(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);
   WRAP(snd_config_delete)(ctx->local_config);
   pthread_mutex_unlock(&cubeb_alsa_mutex);
 }
#ifndef DISABLE_LIBASOUND_DLOPEN
 if (ctx->libasound) {
   dlclose(ctx->libasound);
 }
#endif
 free(ctx);
}

static void
alsa_stream_destroy(cubeb_stream * stm);

static int
alsa_stream_init_single(cubeb * ctx, cubeb_stream ** stream,
                       char const * stream_name, snd_pcm_stream_t stream_type,
                       cubeb_devid deviceid,
                       cubeb_stream_params * 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;
 char const * pcm_name =
     deviceid ? (char const *)deviceid : CUBEB_ALSA_PCM_NAME;

 assert(ctx && stream);

 *stream = NULL;

 if (stream_params->prefs & CUBEB_STREAM_PREF_LOOPBACK) {
   return CUBEB_ERROR_NOT_SUPPORTED;
 }

 switch (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 = *stream_params;
 stm->state = INACTIVE;
 stm->volume = 1.0;
 stm->buffer = NULL;
 stm->bufframes = 0;
 stm->stream_type = stream_type;
 stm->other_stream = NULL;

 r = pthread_mutex_init(&stm->mutex, NULL);
 assert(r == 0);

 r = pthread_cond_init(&stm->cond, NULL);
 assert(r == 0);

 r = alsa_locked_pcm_open(&stm->pcm, pcm_name, stm->stream_type,
                          ctx->local_config);
 if (r < 0) {
   alsa_stream_destroy(stm);
   return CUBEB_ERROR;
 }

 r = WRAP(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 = WRAP(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 = WRAP(snd_pcm_get_params)(stm->pcm, &stm->buffer_size, &period_size);
 assert(r == 0);

 /* Double internal buffer size to have enough space when waiting for the other
  * side of duplex connection */
 stm->buffer_size *= 2;
 stm->buffer =
     calloc(1, WRAP(snd_pcm_frames_to_bytes)(stm->pcm, stm->buffer_size));
 assert(stm->buffer);

 stm->nfds = WRAP(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 = WRAP(snd_pcm_poll_descriptors)(stm->pcm, stm->saved_fds, stm->nfds);
 assert((nfds_t)r == stm->nfds);

 if (alsa_register_stream(ctx, stm) != 0) {
   alsa_stream_destroy(stm);
   return CUBEB_ERROR;
 }

 *stream = stm;

 return CUBEB_OK;
}

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)
{
 int result = CUBEB_OK;
 cubeb_stream *instm = NULL, *outstm = NULL;

 if (result == CUBEB_OK && input_stream_params) {
   result = alsa_stream_init_single(ctx, &instm, stream_name,
                                    SND_PCM_STREAM_CAPTURE, input_device,
                                    input_stream_params, latency_frames,
                                    data_callback, state_callback, user_ptr);
 }

 if (result == CUBEB_OK && output_stream_params) {
   result = alsa_stream_init_single(ctx, &outstm, stream_name,
                                    SND_PCM_STREAM_PLAYBACK, output_device,
                                    output_stream_params, latency_frames,
                                    data_callback, state_callback, user_ptr);
 }

 if (result == CUBEB_OK && input_stream_params && output_stream_params) {
   instm->other_stream = outstm;
   outstm->other_stream = instm;
 }

 if (result != CUBEB_OK && instm) {
   alsa_stream_destroy(instm);
 }

 *stream = outstm ? outstm : instm;

 return result;
}

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;

 if (stm->other_stream) {
   stm->other_stream->other_stream = NULL; // to stop infinite recursion
   alsa_stream_destroy(stm->other_stream);
 }

 pthread_mutex_lock(&stm->mutex);
 if (stm->pcm) {
   if (stm->state == DRAINING) {
     WRAP(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->buffer);

 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;
 }

 assert(stm);

 r = WRAP(snd_pcm_hw_params_any)(stm->pcm, hw_params);
 if (r < 0) {
   return CUBEB_ERROR;
 }

 r = WRAP(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 = WRAP(snd_pcm_open)(&pcm, CUBEB_ALSA_PCM_NAME, SND_PCM_STREAM_PLAYBACK,
                        SND_PCM_NO_AUTO_RESAMPLE);
 if (r < 0) {
   return CUBEB_ERROR;
 }

 r = WRAP(snd_pcm_hw_params_any)(pcm, hw_params);
 if (r < 0) {
   WRAP(snd_pcm_close)(pcm);
   return CUBEB_ERROR;
 }

 r = WRAP(snd_pcm_hw_params_get_rate)(hw_params, rate, &dir);
 if (r >= 0) {
   /* There is a default rate: use it. */
   WRAP(snd_pcm_close)(pcm);
   return CUBEB_OK;
 }

 /* Use a common rate, alsa may adjust it based on hw/etc. capabilities. */
 *rate = 44100;

 r = WRAP(snd_pcm_hw_params_set_rate_near)(pcm, hw_params, rate, NULL);
 if (r < 0) {
   WRAP(snd_pcm_close)(pcm);
   return CUBEB_ERROR;
 }

 WRAP(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;

 if (stm->stream_type == SND_PCM_STREAM_PLAYBACK && stm->other_stream) {
   int r = alsa_stream_start(stm->other_stream);
   if (r != CUBEB_OK)
     return r;
 }

 pthread_mutex_lock(&stm->mutex);
 /* Capture pcm must be started after initial setup/recover */
 if (stm->stream_type == SND_PCM_STREAM_CAPTURE &&
     WRAP(snd_pcm_state)(stm->pcm) == SND_PCM_STATE_PREPARED) {
   WRAP(snd_pcm_start)(stm->pcm);
 }
 WRAP(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;

 if (stm->stream_type == SND_PCM_STREAM_PLAYBACK && stm->other_stream) {
   int r = alsa_stream_stop(stm->other_stream);
   if (r != CUBEB_OK)
     return r;
 }

 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);
 WRAP(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 (WRAP(snd_pcm_state)(stm->pcm) != SND_PCM_STATE_RUNNING ||
     WRAP(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->stream_position >= (snd_pcm_uframes_t)delay) {
   *position = stm->stream_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 (WRAP(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 int
alsa_enumerate_devices(cubeb * context, cubeb_device_type type,
                      cubeb_device_collection * collection)
{
 cubeb_device_info * device = NULL;

 if (!context)
   return CUBEB_ERROR;

 uint32_t rate, max_channels;
 int r;

 r = alsa_get_preferred_sample_rate(context, &rate);
 if (r != CUBEB_OK) {
   return CUBEB_ERROR;
 }

 r = alsa_get_max_channel_count(context, &max_channels);
 if (r != CUBEB_OK) {
   return CUBEB_ERROR;
 }

 char const * a_name = "default";
 device = (cubeb_device_info *)calloc(1, sizeof(cubeb_device_info));
 assert(device);
 if (!device)
   return CUBEB_ERROR;

 device->device_id = a_name;
 device->devid = (cubeb_devid)device->device_id;
 device->friendly_name = a_name;
 device->group_id = a_name;
 device->vendor_name = a_name;
 device->type = type;
 device->state = CUBEB_DEVICE_STATE_ENABLED;
 device->preferred = CUBEB_DEVICE_PREF_ALL;
 device->format = CUBEB_DEVICE_FMT_S16NE;
 device->default_format = CUBEB_DEVICE_FMT_S16NE;
 device->max_channels = max_channels;
 device->min_rate = rate;
 device->max_rate = rate;
 device->default_rate = rate;
 device->latency_lo = 0;
 device->latency_hi = 0;

 collection->device = device;
 collection->count = 1;

 return CUBEB_OK;
}

static int
alsa_device_collection_destroy(cubeb * context,
                              cubeb_device_collection * collection)
{
 assert(collection->count == 1);
 (void)context;
 free(collection->device);
 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,
   .get_supported_input_processing_params = NULL,
   .enumerate_devices = alsa_enumerate_devices,
   .device_collection_destroy = alsa_device_collection_destroy,
   .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_get_input_latency = NULL,
   .stream_set_volume = alsa_stream_set_volume,
   .stream_set_name = NULL,
   .stream_get_current_device = NULL,
   .stream_set_input_mute = NULL,
   .stream_set_input_processing_params = NULL,
   .stream_device_destroy = NULL,
   .stream_register_device_changed_callback = NULL,
   .register_device_collection_changed = NULL};