我有一个关于如何使用线程主循环数据回调功能的问题。我一直在查看文档并尝试一下。为了尝试数据回调，我采用了 AsyncDeviceList 示例，将主循环更改为线程主循环，并尝试在此处使用 pa_threaded_mainloop_signal(ml,1) 和 pa_threaded_mainloop_accept() 进行回调。我不确定我是否将信号（ml，1）放在错误的位置，但程序为我挂起。我注意到在回调调用signal(1) 之后，当wait() 唤醒时，get_state() 的返回值仍然是OPERATION_RUNNING。据我了解，这是有道理的，因为需要调用 accept() 才能使信号继续进行。但是，文档的数据回调示例是这样编码的，所以我 ma 有点迷失了如何正确地去做这件事。一些帮助和澄清会有所帮助。此外，我将在解决后将此示例添加到 pulseaudio wiki 页面。
ps 我复制了下面的代码。编译：'gcc -Wall -o pulsedevicelist pulsedevicelist.c -lpulse' 资源： http ://freedesktop.org/software/pulseaudio/doxygen/threaded_mainloop.html http://www.freedesktop.org/wiki/Software/PulseAudio /Documentation/Developer/Clients/Samples/AsyncDeviceList
#include <stdio.h>
#include <string.h>
#include <pulse/pulseaudio.h>
#include <pulse/stream.h>
// Field list is here: http://0pointer.de/lennart/projects/pulseaudio/doxygen/structpa__sink__info.html
typedef struct pa_devicelist {
uint8_t initialized;
char name[512];
uint32_t index;
char description[256];
} pa_devicelist_t;
void pa_state_cb(pa_context *c, void *userdata);
void pa_sinklist_cb(pa_context *c, const pa_sink_info *l, int eol, void *userdata);
void pa_sourcelist_cb(pa_context *c, const pa_source_info *l, int eol, void *userdata);
int pa_get_devicelist(pa_devicelist_t *input, pa_devicelist_t *output);
pa_threaded_mainloop *pa_ml;
int main(int argc, char *argv[]) {
int ctr;
// This is where we'll store the input device list
pa_devicelist_t pa_input_devicelist[16];
// This is where we'll store the output device list
pa_devicelist_t pa_output_devicelist[16];
if (pa_get_devicelist(pa_input_devicelist, pa_output_devicelist) < 0) {
fprintf(stderr, "failed to get device list\n");
return 1;
}
for (ctr = 0; ctr < 16; ctr++) {
if (! pa_output_devicelist[ctr].initialized) {
break;
}
printf("=======[ Output Device #%d ]=======\n", ctr+1);
printf("Description: %s\n", pa_output_devicelist[ctr].description);
printf("Name: %s\n", pa_output_devicelist[ctr].name);
printf("Index: %d\n", pa_output_devicelist[ctr].index);
printf("\n");
}
for (ctr = 0; ctr < 16; ctr++) {
if (! pa_input_devicelist[ctr].initialized) {
break;
}
printf("=======[ Input Device #%d ]=======\n", ctr+1);
printf("Description: %s\n", pa_input_devicelist[ctr].description);
printf("Name: %s\n", pa_input_devicelist[ctr].name);
printf("Index: %d\n", pa_input_devicelist[ctr].index);
printf("\n");
}
return 0;
}
int pa_get_devicelist(pa_devicelist_t *input, pa_devicelist_t *output) {
// Define our pulse audio loop and connection variables
//pa_threaded_mainloop *pa_ml;
pa_mainloop_api *pa_mlapi;
pa_operation *pa_op;
pa_context *pa_ctx;
pa_operation_state_t temp;
// We'll need these state variables to keep track of our requests
int state = 0;
int pa_ready = 0;
// Initialize our device lists
memset(input, 0, sizeof(pa_devicelist_t) * 16);
memset(output, 0, sizeof(pa_devicelist_t) * 16);
// Create a mainloop API and connection to the default server
pa_ml = pa_threaded_mainloop_new();
pa_mlapi = pa_threaded_mainloop_get_api(pa_ml);
pa_ctx = pa_context_new(pa_mlapi, "test");
//pa_stream *s = pa_stream_new(pa_ctx, "stream", &ss, &map);
// This function connects to the pulse server
pa_context_connect(pa_ctx, NULL, PA_CONTEXT_NOFLAGS, NULL);
// This function defines a callback so the server will tell us it's state.
// Our callback will wait for the state to be ready. The callback will
// modify the variable to 1 so we know when we have a connection and it's
// ready.
// If there's an error, the callback will set pa_ready to 2
pa_context_set_state_callback(pa_ctx, pa_state_cb, &pa_ready);
pa_threaded_mainloop_start(pa_ml);
// Now we'll enter into an infinite loop until we get the data we receive
// or if there's an error
for (;;) {
// We can't do anything until PA is ready, so just iterate the mainloop
// and continue
if (pa_ready == 0) {
//pa_mainloop_iterate(pa_ml, 1, NULL);
continue;
}
// We couldn't get a connection to the server, so exit out
if (pa_ready == 2) {
pa_context_disconnect(pa_ctx);
pa_context_unref(pa_ctx);
pa_threaded_mainloop_free(pa_ml);
return -1;
}
// At this point, we're connected to the server and ready to make
// requests
switch (state) {
// State 0: we haven't done anything yet
case 0:
// This sends an operation to the server. pa_sinklist_info is
// our callback function and a pointer to our devicelist will
// be passed to the callback The operation ID is stored in the
// pa_op variable
pa_threaded_mainloop_lock(pa_ml);
pa_op = pa_context_get_sink_info_list(pa_ctx,
pa_sinklist_cb,
output
);
while (pa_operation_get_state(pa_op) == PA_OPERATION_RUNNING) { // MF
temp = pa_operation_get_state(pa_op); // MF
pa_threaded_mainloop_wait(pa_ml); // MF
} // MF
// Update state for next iteration through the loop
state++;
break;
case 1:
// Now we wait for our operation to complete. When it's
// complete our pa_output_devicelist is filled out, and we move
// along to the next state
if (pa_operation_get_state(pa_op) == PA_OPERATION_DONE) {
pa_operation_unref(pa_op);
pa_threaded_mainloop_accept(pa_ml); // MF
pa_threaded_mainloop_unlock(pa_ml); // MF
// Now we perform another operation to get the source
// (input device) list just like before. This time we pass
// a pointer to our input structure
pa_threaded_mainloop_lock(pa_ml);
pa_op = pa_context_get_source_info_list(pa_ctx,
pa_sourcelist_cb,
input
);
// Update the state so we know what to do next
state++;
}
break;
case 2:
if (pa_operation_get_state(pa_op) == PA_OPERATION_DONE) {
// Now we're done, clean up and disconnect and return
pa_operation_unref(pa_op);
pa_context_disconnect(pa_ctx);
pa_context_unref(pa_ctx);
pa_threaded_mainloop_free(pa_ml);
return 0;
}
break;
default:
// We should never see this state
fprintf(stderr, "in state %d\n", state);
return -1;
}
// Iterate the main loop and go again. The second argument is whether
// or not the iteration should block until something is ready to be
// done. Set it to zero for non-blocking.
//pa_mainloop_iterate(pa_ml, 1, NULL);
}
}
// This callback gets called when our context changes state. We really only
// care about when it's ready or if it has failed
void pa_state_cb(pa_context *c, void *userdata) {
pa_context_state_t state;
int *pa_ready = (int *)userdata;
state = pa_context_get_state(c);
switch (state) {
// There are just here for reference
case PA_CONTEXT_UNCONNECTED:
case PA_CONTEXT_CONNECTING:
case PA_CONTEXT_AUTHORIZING:
case PA_CONTEXT_SETTING_NAME:
default:
break;
case PA_CONTEXT_FAILED:
case PA_CONTEXT_TERMINATED:
*pa_ready = 2;
break;
case PA_CONTEXT_READY:
*pa_ready = 1;
break;
}
}
// pa_mainloop will call this function when it's ready to tell us about a sink.
// Since we're not threading, there's no need for mutexes on the devicelist
// structure
void pa_sinklist_cb(pa_context *c, const pa_sink_info *l, int eol, void *userdata) {
pa_devicelist_t *pa_devicelist = (pa_devicelist_t *)userdata;
int ctr = 0;
// If eol is set to a positive number, you're at the end of the list
if (eol > 0) {
pa_threaded_mainloop_signal(pa_ml, 1); // MF
return;
}
// We know we've allocated 16 slots to hold devices. Loop through our
// structure and find the first one that's "uninitialized." Copy the
// contents into it and we're done. If we receive more than 16 devices,
// they're going to get dropped. You could make this dynamically allocate
// space for the device list, but this is a simple example.
for (ctr = 0; ctr < 16; ctr++) {
if (! pa_devicelist[ctr].initialized) {
strncpy(pa_devicelist[ctr].name, l->name, 511);
strncpy(pa_devicelist[ctr].description, l->description, 255);
pa_devicelist[ctr].index = l->index;
pa_devicelist[ctr].initialized = 1;
break;
}
}
}
// See above. This callback is pretty much identical to the previous
void pa_sourcelist_cb(pa_context *c, const pa_source_info *l, int eol, void *userdata) {
pa_devicelist_t *pa_devicelist = (pa_devicelist_t *)userdata;
int ctr = 0;
if (eol > 0) {
return;
}
for (ctr = 0; ctr < 16; ctr++) {
if (! pa_devicelist[ctr].initialized) {
strncpy(pa_devicelist[ctr].name, l->name, 511);
strncpy(pa_devicelist[ctr].description, l->description, 255);
pa_devicelist[ctr].index = l->index;
pa_devicelist[ctr].initialized = 1;
break;
}
}
}