snd_pcm_plugin_flush()

Finish processing all pending data in a PCM channel's queue and stop the channel

Synopsis:

#include <sys/asoundlib.h>

int snd_pcm_plugin_flush( snd_pcm_t *handle, 
                          int        channel );

Arguments:

handle
The handle for the PCM device, which you must have opened by calling snd_pcm_open_name(), snd_pcm_open(), or snd_pcm_open_preferred().
channel
The channel; SND_PCM_CHANNEL_CAPTURE or SND_PCM_CHANNEL_PLAYBACK.

Library:

libasound.so

Use the -l asound option to qcc to link against this library.

Description:

The snd_pcm_plugin_flush() function flushes all unprocessed data in the driver queue:

If you use this call to process playback data, there are two considerations:
  • Since this call is a blocking call, if the channel is in the SND_PCM_STATUS_SUSPENDED state, an error occurs if you call this function.
  • If this function is called while in the SND_PCM_STATUS_PAUSED state while processing playback data, playback is resumed and the channel goes into the SND_PCM_STATUS_RUNNING state immediately, and then ends in the SND_PCM_STATUS_READY state.

    If the channel doesn't start playing (not enough data has been written to start playback), then this call silences the remainder of the buffer to satisfy the playback start requirements. Once the playback requirements are satisfied, playback starts and allows the data to be played out. Once the buffer empties, this call returns successfully.

If this call completes successfully, the channel is left in the SND_PCM_STATUS_READY state.

Returns:

A positive number on success, or a negative value on error.

Errors:

-EAGAIN
The state was SND_PCM_STATUS_SUSPENDED while trying to call this function. This error is also returned if the state was SND_PCM_STATUS_PAUSED, but resuming the playback failed.
-EINVAL
The state of handle is invalid, an invalid channel was provided as input,or an invalid state change occurred. You can call snd_pcm_plugin_status() to check if the state change was invalid.
-EINTR
The operation was interrupted because of a system signal (such as a timer) or an error was returned asynchronously.

Classification:

QNX Neutrino

Safety:  
Cancellation point No
Interrupt handler No
Signal handler Yes
Thread Read the Caveats

Caveats:

This function is not thread safe if handle (snd_pcm_t) is used across multiple threads.

Because the plugin interface may be subbuffering the written data until a complete driver block can be assembled, the flush call may have to inject up to (blocksize-1) samples into the channel so that the last block can be sent to the driver for playing. For this reason, the flush call may return a positive value indicating that this silence had to be inserted.

This function is the plugin-aware version of snd_pcm_channel_flush() . It functions exactly the same way, with the above caveat. However, make sure that you don't mix and match plugin- and nonplugin-aware functions in your application, or you may get undefined behavior and misleading results.