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ALSA: Experiment with snd_pcm_link().

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This commit is contained in:
David Reid
2026-01-08 17:41:58 +10:00
parent 597654dcf6
commit 0b4a861d94
1 changed files with 43 additions and 29 deletions
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miniaudio.h
+43 -29
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@@ -27982,6 +27982,7 @@ typedef void (* ma_snd_lib_error_handler_t)(const char* file, int line, const ch
typedef int (* ma_snd_lib_error_set_handler_proc) (ma_snd_lib_error_handler_t handler);
typedef int (* ma_snd_pcm_open_proc) (ma_snd_pcm_t **pcm, const char *name, ma_snd_pcm_stream_t stream, int mode);
typedef int (* ma_snd_pcm_close_proc) (ma_snd_pcm_t *pcm);
typedef int (* ma_snd_pcm_link_proc) (ma_snd_pcm_t* pcm1, ma_snd_pcm_t* pcm2);
typedef size_t (* ma_snd_pcm_hw_params_sizeof_proc) (void);
typedef int (* ma_snd_pcm_hw_params_any_proc) (ma_snd_pcm_t *pcm, ma_snd_pcm_hw_params_t *params);
typedef int (* ma_snd_pcm_hw_params_current_proc) (ma_snd_pcm_t *pcm, ma_snd_pcm_hw_params_t *params);
@@ -28077,6 +28078,7 @@ typedef struct ma_context_state_alsa
ma_snd_lib_error_set_handler_proc snd_lib_error_set_handler;
ma_snd_pcm_open_proc snd_pcm_open;
ma_snd_pcm_close_proc snd_pcm_close;
ma_snd_pcm_link_proc snd_pcm_link;
ma_snd_pcm_hw_params_sizeof_proc snd_pcm_hw_params_sizeof;
ma_snd_pcm_hw_params_any_proc snd_pcm_hw_params_any;
ma_snd_pcm_hw_params_current_proc snd_pcm_hw_params_current;
@@ -28157,6 +28159,7 @@ typedef struct ma_device_state_alsa
int pollDescriptorCountCapture;
ma_bool8 isUsingMMapPlayback;
ma_bool8 isUsingMMapCapture;
ma_bool8 isLinked; /* Only relevant for duplex mode. Used to indicate that the capture and playback PCMs are linked with snd_pcm_link(). */
} ma_device_state_alsa;
@@ -28506,6 +28509,7 @@ static ma_result ma_context_init__alsa(ma_context* pContext, const void* pContex
pContextStateALSA->snd_lib_error_set_handler = (ma_snd_lib_error_set_handler_proc )ma_dlsym(pLog, pContextStateALSA->asoundSO, "snd_lib_error_set_handler");
pContextStateALSA->snd_pcm_open = (ma_snd_pcm_open_proc )ma_dlsym(pLog, pContextStateALSA->asoundSO, "snd_pcm_open");
pContextStateALSA->snd_pcm_close = (ma_snd_pcm_close_proc )ma_dlsym(pLog, pContextStateALSA->asoundSO, "snd_pcm_close");
pContextStateALSA->snd_pcm_link = (ma_snd_pcm_link_proc )ma_dlsym(pLog, pContextStateALSA->asoundSO, "snd_pcm_link");
pContextStateALSA->snd_pcm_hw_params_sizeof = (ma_snd_pcm_hw_params_sizeof_proc )ma_dlsym(pLog, pContextStateALSA->asoundSO, "snd_pcm_hw_params_sizeof");
pContextStateALSA->snd_pcm_hw_params_any = (ma_snd_pcm_hw_params_any_proc )ma_dlsym(pLog, pContextStateALSA->asoundSO, "snd_pcm_hw_params_any");
pContextStateALSA->snd_pcm_hw_params_current = (ma_snd_pcm_hw_params_current_proc )ma_dlsym(pLog, pContextStateALSA->asoundSO, "snd_pcm_hw_params_current");
@@ -28579,6 +28583,7 @@ static ma_result ma_context_init__alsa(ma_context* pContext, const void* pContex
ma_snd_lib_error_set_handler_proc _snd_lib_error_set_handler = snd_lib_error_set_handler;
ma_snd_pcm_open_proc _snd_pcm_open = snd_pcm_open;
ma_snd_pcm_close_proc _snd_pcm_close = snd_pcm_close;
ma_snd_pcm_link_proc _snd_pcm_link = snd_pcm_link;
ma_snd_pcm_hw_params_sizeof_proc _snd_pcm_hw_params_sizeof = snd_pcm_hw_params_sizeof;
ma_snd_pcm_hw_params_any_proc _snd_pcm_hw_params_any = snd_pcm_hw_params_any;
ma_snd_pcm_hw_params_current_proc _snd_pcm_hw_params_current = snd_pcm_hw_params_current;
@@ -28649,6 +28654,7 @@ static ma_result ma_context_init__alsa(ma_context* pContext, const void* pContex
pContextStateALSA->snd_lib_error_set_handler = _snd_lib_error_set_handler;
pContextStateALSA->snd_pcm_open = _snd_pcm_open;
pContextStateALSA->snd_pcm_close = _snd_pcm_close;
pContextStateALSA->snd_pcm_link = _snd_pcm_link;
pContextStateALSA->snd_pcm_hw_params_sizeof = _snd_pcm_hw_params_sizeof;
pContextStateALSA->snd_pcm_hw_params_any = _snd_pcm_hw_params_any;
pContextStateALSA->snd_pcm_hw_params_current = _snd_pcm_hw_params_current;
@@ -29648,6 +29654,15 @@ static ma_result ma_device_init__alsa(ma_device* pDevice, const void* pDeviceBac
}
/* Link the PCMs in duplex mode. */
if (deviceType == ma_device_type_duplex) {
resultALSA = pContextStateALSA->snd_pcm_link(pDeviceStateALSA->pPCMCapture, pDeviceStateALSA->pPCMPlayback);
if (resultALSA == 0) {
pDeviceStateALSA->isLinked = MA_TRUE;
}
}
*ppDeviceState = pDeviceStateALSA;
return MA_SUCCESS;
@@ -29689,21 +29704,23 @@ static ma_result ma_device_start__alsa(ma_device* pDevice)
}
}
if (pDeviceStateALSA->pPCMPlayback != NULL) {
/*
When data is written to the device we wait for the device to get ready to receive data with poll(). In my testing
I have observed that poll() can sometimes block forever unless the device is started explicitly with snd_pcm_start()
or some data is written with snd_pcm_writei().
if (ma_device_get_type(pDevice) != ma_device_type_duplex || !pDeviceStateALSA->isLinked) { /* <-- In duplex mode the PCMs are linked which means the playback side will be started when the capture side starts. */
if (pDeviceStateALSA->pPCMPlayback != NULL) {
/*
When data is written to the device we wait for the device to get ready to receive data with poll(). In my testing
I have observed that poll() can sometimes block forever unless the device is started explicitly with snd_pcm_start()
or some data is written with snd_pcm_writei().
To resolve this I've decided to do an explicit start with snd_pcm_start(). The problem with this is that the device
is started without any data in the internal buffer which will result in an immediate underrun. If instead we were
to call into snd_pcm_writei() in an attempt to prevent the underrun, we would run the risk of a weird deadlock
issue as documented inside ma_device_write__alsa().
*/
resultALSA = pContextStateALSA->snd_pcm_start(pDeviceStateALSA->pPCMPlayback);
if (resultALSA < 0) {
ma_log_post(ma_device_get_log(pDevice), MA_LOG_LEVEL_ERROR, "[ALSA] Failed to start playback device.");
return ma_result_from_errno(-resultALSA);
To resolve this I've decided to do an explicit start with snd_pcm_start(). The problem with this is that the device
is started without any data in the internal buffer which will result in an immediate underrun. If instead we were
to call into snd_pcm_writei() in an attempt to prevent the underrun, we would run the risk of a weird deadlock
issue as documented inside ma_device_write__alsa().
*/
resultALSA = pContextStateALSA->snd_pcm_start(pDeviceStateALSA->pPCMPlayback);
if (resultALSA < 0) {
ma_log_post(ma_device_get_log(pDevice), MA_LOG_LEVEL_ERROR, "[ALSA] Failed to start playback device.");
return ma_result_from_errno(-resultALSA);
}
}
}
@@ -29717,11 +29734,6 @@ static ma_result ma_device_stop__alsa(ma_device* pDevice)
int resultPoll;
int resultRead;
/*
The stop callback will get called on the worker thread after read/write__alsa() has returned. At this point there is
a small chance that our wakeupfd has not been cleared. We'll clear that out now if applicable.
*/
if (pDeviceStateALSA->pPCMCapture != NULL) {
ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[ALSA] Dropping capture device...");
pContextStateALSA->snd_pcm_drop(pDeviceStateALSA->pPCMCapture);
@@ -29736,17 +29748,19 @@ static ma_result ma_device_stop__alsa(ma_device* pDevice)
}
}
if (pDeviceStateALSA->pPCMPlayback != NULL) {
ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[ALSA] Dropping playback device...");
pContextStateALSA->snd_pcm_drop(pDeviceStateALSA->pPCMPlayback);
ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[ALSA] Dropping playback device successful.");
if (ma_device_get_type(pDevice) != ma_device_type_duplex && pDeviceStateALSA->isLinked) { /* <-- In duplex mode the PCMs are linked which means the playback side will be stopped when the capture side starts. */
if (pDeviceStateALSA->pPCMPlayback != NULL) {
ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[ALSA] Dropping playback device...");
pContextStateALSA->snd_pcm_drop(pDeviceStateALSA->pPCMPlayback);
ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[ALSA] Dropping playback device successful.");
/* We need to prepare the device again, otherwise we won't be able to restart the device. */
ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[ALSA] Preparing playback device...");
if (pContextStateALSA->snd_pcm_prepare(pDeviceStateALSA->pPCMPlayback) < 0) {
ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[ALSA] Preparing playback device failed.");
} else {
ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[ALSA] Preparing playback device successful.");
/* We need to prepare the device again, otherwise we won't be able to restart the device. */
ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[ALSA] Preparing playback device...");
if (pContextStateALSA->snd_pcm_prepare(pDeviceStateALSA->pPCMPlayback) < 0) {
ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[ALSA] Preparing playback device failed.");
} else {
ma_log_postf(ma_device_get_log(pDevice), MA_LOG_LEVEL_DEBUG, "[ALSA] Preparing playback device successful.");
}
}
}