Related
I'm trying to replicate the behavior of a Windows app on Linux. Specifically, to control the backlighting on a keyboard.
Using Wireshark (on the linux host) to observer what the Windows tool does (when run on a Windows guest), I see a pair of URB_INTERRUPT out messages followed by a pair of URB_INTERRUPT in messages (one of each in each direction).
I've never used libusb before, but reading docs and examples, I've put together the code below. When run, libusb_interrupt_transfer() returns LIBUSB_ERROR_IO. Maybe I'm passing the wrong parameters, maybe I missed some initialization step, this is where my lack of experience with libusb really shines.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libusb-1.0/libusb.h>
int main(int argc, char *argv[]) {
unsigned int interface = 2;
int bSent = 0;
int retval = 0;
unsigned char msg[64];
unsigned char bytes[] = "\x51\x2c\x00\x00\xff\x64\x00\xff\xff\x72\x67\x62";
bzero(msg, sizeof(msg));
memcpy(msg, bytes, sizeof(bytes));
libusb_device_handle *devh;
libusb_init(NULL);
devh = libusb_open_device_with_vid_pid(NULL, 0x0b05, 0x1875);
if (devh) {
printf("Found device\n");
} else {
printf("ERROR: can't find device\n");
exit(1);
}
retval = libusb_set_auto_detach_kernel_driver(devh, interface);
if (!retval) {
printf("Set auto detach kernel driver\n");
} else {
printf("ERROR: failed to set auto detach kernel driver: %s\n", libusb_strerror(retval));
exit(1);
}
retval = libusb_claim_interface(devh, interface);
if (retval < 0) {
printf("ERROR: failed to claim interface %d: %s\n", interface, libusb_strerror(retval));
exit(1);
} else {
printf("Claimed interface %d\n", interface);
}
retval = libusb_interrupt_transfer(devh, interface, msg, sizeof(msg), &bSent, 1000);
if (retval < 0) {
printf("ERROR: libusb_interrupt_transfer() returned %d: %s\n", retval, libusb_strerror(retval));
} else {
printf("libusb_interrupt_transfer() sent %d bytes\n", bSent);
}
libusb_release_interface(devh, interface);
libusb_close(devh);
libusb_exit(NULL);
return(0);
}
Output:
Found device
Set auto detach kernel driver
Claimed interface 2
ERROR: libusb_interrupt_transfer() returned -1: Input/Output Error
SDL capture audio callbacks seem to be called once for every 12 playback callbacks. Am I doing something wrong? This feels like an SDL or PulseAudio bug.
The program below prints "Reading audio..." once every ~12 "Writing audio..." prints. Tested via running the command directly, through gdb, and through Valgrind.
I've tried this in both C and Golang (using github.com/veandco/go-sdl2/sdl), on the same machine.
C code:
// A test program to copy audio in (microphone) to audio out (speaker) via SDL.
//
// Compile: cc inout.c -o inout -lSDL2
// Run: ./inout
#include <SDL2/SDL.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#define BUF_SIZE 1024
// Stereo float32 samples.
static uint8_t saved[BUF_SIZE*2*sizeof(float)];
// Copies audio callback data into the saved buffer.
void audioReader(void* udata, uint8_t* buf, int len) {
fprintf(stderr, "Reading audio: %d -> %ld bytes\n", len, sizeof(saved));
memcpy(saved, buf, len);
}
// Copies saved audio data into the callback buffer.
void audioWriter(void* udata, uint8_t* buf, int len) {
fprintf(stderr, "Writing audio: %ld -> %d bytes\n", sizeof(saved), len);
memcpy(buf, saved, len);
}
// List all devices of the given type, and return the name of the first or NULL.
// Caller must free the returned pointer.
char* ChooseDevice(int is_capture) {
int dev_cnt = SDL_GetNumAudioDevices(is_capture);
if (dev_cnt < 1) {
fprintf(stderr, "No %s devices: %s\n", is_capture ? "capture" : "playback", SDL_GetError());
return NULL;
}
printf("%s devices:\n", is_capture ? "capture" : "playback");
char* dev_name = NULL;
for (int i = 0; i < dev_cnt; i++) {
printf("%c %s\n", !dev_name ? '*' : ' ', SDL_GetAudioDeviceName(i, is_capture));
if (!dev_name) {
const char* tmp = SDL_GetAudioDeviceName(i, is_capture);
dev_name = malloc(strlen(tmp)+1);
strcpy(dev_name, tmp);
}
}
if (!dev_name) {
fprintf(stderr, "No %s devices\n", is_capture ? "capture" : "playback");
}
return dev_name;
}
// Opens and unpauses the first device of the given type, returning its ID, or
// returns 0.
SDL_AudioDeviceID OpenDevice(int is_capture) {
char* dev_name = ChooseDevice(is_capture);
if (!dev_name) return 0;
SDL_AudioSpec spec;
SDL_memset(&spec, 0, sizeof(spec));
spec.freq = 48000;
spec.format = AUDIO_F32;
spec.channels = 2;
spec.samples = BUF_SIZE;
spec.callback = is_capture ? audioReader : audioWriter;
SDL_AudioDeviceID dev_id = SDL_OpenAudioDevice(dev_name, is_capture, &spec, NULL, 0);
if (dev_id == 0) {
fprintf(stderr, "Failed to open %s device %s: %s\n", is_capture ? "input" : "output", dev_name, SDL_GetError());
return 0;
}
free(dev_name);
SDL_PauseAudioDevice(dev_id, SDL_FALSE);
return dev_id;
}
int main(int argc, char** argv) {
SDL_memset(saved, 0, sizeof(saved));
if (SDL_Init(SDL_INIT_AUDIO) < 0) {
fprintf(stderr, "Failed to initialize SDL audio: %s\n", SDL_GetError());
return 1;
}
SDL_AudioDeviceID in_dev_id = OpenDevice(/* is_capture = */ SDL_TRUE);
if (in_dev_id == 0) return 1;
SDL_AudioDeviceID out_dev_id = OpenDevice(/* is_capture = */ SDL_FALSE);
if (out_dev_id == 0) return 1;
SDL_Delay(10000); // 10 seconds
SDL_CloseAudioDevice(in_dev_id);
SDL_CloseAudioDevice(out_dev_id);
SDL_Quit();
return 0;
}
I'm new to Stackoverflow and c and pulseaudio. Thanks for all help.
I get a the Segmentation fault (core dumped) error in the mainloop of a custom pulseaudiolib code. It it takes 1 to 30s to apear.
I am trying to get the audio data of a custom sink
pacmd load-module module-null-sink sink_name=MySink
pacmd update-sink-proplist MySink device.description=MySink
pacmd load-module module-loopback sink=MySink
use its data and pip it back to the speaker.
I'm pretty new at C and pulseaudio so I used the doc and https://menno.io/posts/pulseaudio_monitoring/
This is my code:
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <pulse/simple.h>
#include <pulse/error.h>
#include <pulse/context.h>
#include <pulse/def.h>
#include <pulse/format.h>
#include <pulse/introspect.h>
#include <pulse/stream.h>
#include <pulse/thread-mainloop.h>
const char * SINKNAME = "MySink";
const char * SPEAKNAME = "alsa_output.pci-0000_05_00.6.analog-stereo";
char found = 0;
const uint32_t RATE = 344;
pa_stream * gStream = NULL;
void stream_read_cb(pa_stream *stream, size_t length, void *index_incr){
printf("in read\n");
const void * samples[length];
size_t * leng;
(*leng) = length;
printf("length : %d, %d\n",length,(*leng));
int res = pa_stream_peek(stream, samples, leng);
pa_stream_drop(stream);
if(gStream != NULL){
int result = pa_stream_write( gStream, samples,length, NULL,0, PA_SEEK_RELATIVE);
}
printf("[");
if (res == 0){
for(int i = 0 ; i< length; i++){
printf("%d,",samples[i]);
}
}
printf("]\n");
}
void sink_info_cb(pa_context* context, const pa_sink_info *sink_info_p, int eol, void *userdata){
printf( "in sinkinfo\n");
const pa_sink_info* sink_info = sink_info_p;
if(found !=1){
printf( "index: %d\n", (*sink_info).index);
printf("help\n");
printf( "name: %s\n", (*sink_info).name);
printf( "description: %s\n", (*sink_info).description);
printf("searchName: %s\n",SINKNAME);
if (strcmp((*sink_info).name, SINKNAME) == 0){
found = 1;
// Found the sink we want to monitor for peak levels.
// Tell PA to call stream_read_cb with peak samples.
printf( "setting up peak recording using: %s\n ", (*sink_info).monitor_source_name);
pa_sample_spec *samplespec;
(*samplespec).channels = 1;
(*samplespec).format = PA_SAMPLE_U8;
(*samplespec).rate = RATE;
pa_stream * stream = pa_stream_new(context, "peak detect demo", samplespec, NULL);
pa_stream_set_read_callback(stream,
stream_read_cb,
( *sink_info).index);
pa_stream_connect_record(stream,
(*sink_info).monitor_source_name,
NULL,
PA_STREAM_PEAK_DETECT);
printf("settetd \n");
}/*
if((*sink_info).name[0] == 'a'){
//printf( "setting up peak recording using: %s\n ", (*sink_info).monitor_source_name);
//pa_sample_spec *samplespec;
// (*samplespec).channels = 1;
// (*samplespec).format = PA_SAMPLE_U8;
// (*samplespec).rate = RATE;
printf("set gStream");
//gStream = pa_stream_new(context, "peak detect demo", samplespec, NULL);
//printf("gSteam setted\n");
}*/
printf("out sink\n");
}
}
void context_notify_cb(pa_context *context, void *userdata){
printf("in context\n");
pa_context_state_t state = pa_context_get_state(context);
if( state == PA_CONTEXT_READY){
printf( "Pulseaudio connection ready...");
// Connected to Pulseaudio. Now request that sink_info_cb
// be called with information about the available sinks.
pa_operation * o = pa_context_get_sink_info_list(context, sink_info_cb, userdata);
pa_operation_unref(o);
}
else if( state == PA_CONTEXT_FAILED){
printf( "Connection failed");
}
else if( state == PA_CONTEXT_TERMINATED){
printf( "Connection terminated");
}
printf("out context\n");
}
void init(){
// Wrap callback methods in appropriate ctypefunc instances so
// that the Pulseaudio C API can call them
printf("in init\n");
pa_context_notify_cb_t _context_notify_cb;
//context_notify_cb(context_notify_cb void ** userdata);
pa_sink_info_cb_t(sink_info_cb);
pa_stream_request_cb_t(stream_read_cb);
// Create the mainloop thread and set our context_notify_cb
// method to be called when there's updates relating to the
// connection to Pulseaudio
pa_threaded_mainloop* _mainloop = pa_threaded_mainloop_new();
pa_mainloop_api* _mainloop_api = pa_threaded_mainloop_get_api(_mainloop);
pa_context *context = pa_context_new(_mainloop_api, "peak_demo");
pa_context_set_state_callback(context, context_notify_cb,NULL);
pa_context_connect(context, NULL, 0, NULL);
pa_threaded_mainloop_start(_mainloop);
printf("out intit\n");
}
int main(int argc, char*argv[]) {
init();
printf("Hello World\n");
while(1){
;
}
printf("end World\n");
return 0;
}
if I try to uncomment
/*
if((*sink_info).name[0] == 'a'){
//printf( "setting up peak recording using: %s\n ", (*sink_info).monitor_source_name);
//pa_sample_spec *samplespec;
// (*samplespec).channels = 1;
// (*samplespec).format = PA_SAMPLE_U8;
// (*samplespec).rate = RATE;
printf("set gStream");
//gStream = pa_stream_new(context, "peak detect demo", samplespec, NULL);
//printf("gSteam setted\n");
}
*/
the error shots like directly.
the output:
...
in read
length : 1, 1
[-1261830080,]
in read
length : 6, 6
[-1246625728,-1017902384,0,0,-1017902304,591610535,]
in read
length : 1, 1
[-1259864000,]
in read
length : 6, 6
[-1227227072,-1017902384,0,0,-1017902304,591610535,]
in read
length : 1, 1
[-1255800768,]
in read
length : 6, 6
[-1234960320,-1017902384,0,0,-1017902304,591610535,]
in read
length : 7, 7
[-1249247168,-939474438,-1017902512,-1017902384,0,0,-1017902304,]
in read
length : 7, 7
[-1242693568,-939474438,-1017902464,-1017902336,0,0,-1017902256,]
Segmentation fault (core dumped)
the uncomment output:
in init
in context
out context
out intit
Hello World
in context
out context
in context
out context
in context
Pulseaudio connection ready...out context
in sinkinfo
index: 0
help
name: alsa_output.pci-0000_05_00.6.analog-stereo
description: Family 17h (Models 10h-1fh) HD Audio Controller Analog Stereo
searchName: MySink
set gStreamout sink
in sinkinfo
index: 1
help
name: MySink
description: MySink
searchName: MySink
setting up peak recording using: MySink.monitor
settetd
Segmentation fault (core dumped)
I need to read a file from a separate thread, to avoid hiccups in the flow of my opengl program. I already do that for loading textures and blending them using global variables, that works fine.
However now I need some separate threads to read small data files.
I have created a struct, which basically contains 2 args and 1 result.
It seems I can't do that or I got it wrong somewhere (or in many places)
Here is the sample code of my non proof of concept:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <pthread.h>
#define content_file "/home/tias/content.txt" //this file contains "foobar!!"
typedef struct {
int* reading; // 0 = not reading , 1 = reading , 2 = finished reading
char* content; // content of the file
char* file; // file to read
} struct_file_content;
struct_file_content first_file;
void *thread_read_file ( void* data ) {
struct_file_content *thisdata = (struct_file_content*) data;
long length;
int i = 0;
char readchar;
char * thiscontent = 0;
int reading_finished = 2;
int *ptr_to_reading_finished = (int*)malloc(sizeof(int));
ptr_to_reading_finished = &reading_finished;
fprintf(stdout,"thread_Read_file called with file: %s and reading: %u\n",(*thisdata).file,*(*thisdata).reading);
FILE * f = fopen ((*thisdata).file, "r");
if (f) {
fseek (f, 0, SEEK_END);
length = ftell (f);
fseek (f, 0, SEEK_SET);
if (length > 39) {
fprintf(stderr,"file %s is too big\n",(*thisdata).file);
exit (1);
}
thiscontent = (char*) malloc (length*sizeof(char));
if ( thiscontent ) {
fread (thiscontent, 1, length, f);
}
fclose (f);
thisdata->content = thiscontent;
} else {
fprintf (stderr, "cannot read file %s\n",(*thisdata).file);
exit (1);
}
sleep(1);
thisdata->reading = ptr_to_reading_finished;
fprintf(stdout,"finished reading: %u\n",*(*thisdata).reading);
fprintf(stdout,"content: %s\n",thiscontent);
pthread_exit(NULL);
return NULL;
}
main()
{
pthread_t thread1;
int filename_length = strlen(content_file);
int rfinish = 2;
int rbegin = 1;
first_file.reading = (int*) malloc(sizeof(int));
first_file.file = (char*) malloc((filename_length+1)*sizeof(char));
first_file.reading = &rbegin;
strcpy(first_file.file,content_file);
pthread_create( &thread1, NULL, thread_read_file, (void*) &first_file);
while ( *(first_file.reading) != 2 ) {
fprintf(stdout,"still reading, reading: %u\n",*(first_file.reading));
sleep(1);
}
fprintf(stdout,"exited control loop with file: %s, reading: %u, content: %s\n",first_file.file, *(first_file.reading), first_file.content);
}
Here's the result:
~/repository/thread/test$ ./tt
still reading, reading: 1
thread_Read_file called with file: /home/tias/content.txt and reading: 1
still reading, reading: 1
still reading, reading: 1
still reading, reading: 1
finished reading: 2
content: foobar!!
still reading, reading: 0
still reading, reading: 0
I was expecting reading = 2 to get out of the loop, instead it is 0.
Any idea on what I have to modify to make it work?
I have read about mutex and so, may be it is the way?
I had found my solution elegant and not working, your help is greatly appreciated.
typedef struct {
int* reading; // 0 = not reading , 1 = reading , 2 = finished reading
char* content; // content of the file
char* file; // file to read
} struct_file_content;
Why is reading a pointer type? It is used in the code as a flag, there is absolutely no need to make it a pointer, especially given that you dynamically allocate memory for this structure field. It complicates the design and is unnecessary. Go ahead and make that an int, not a pointer:
typedef struct {
int reading; // 0 = not reading , 1 = reading , 2 = finished reading
char *content; // content of the file
char *file; // file to read
} struct_file_content;
This simplifies the code in main() used to set up first_file:
first_file.reading = 1;
first_file.content = NULL;
first_file.file = content_file;
Note that there is no need to have first_file.file be dynamically allocated memory, since you know the file name (and size) at compile time. Keep things simple.
Next, you ignore a possible error return value from pthread_create(3). It returns non-zero in case of failure, and you should check for that. Something like this will do:
pthread_t thread1;
int thread_res = pthread_create(&thread1, NULL, thread_read_file, &first_file);
if (thread_res != 0) {
fprintf(stderr, "pthread_create(3) error: %s\n", strerror(thread_res));
exit(EXIT_FAILURE);
}
The code to wait for reading to finish is buggy and racy, you need to either synchronize access to the reading field of struct_file_content with a mutex, or properly wait for the thread to terminate before accessing the first_file again. Since the code does nothing but wait for the thread, pthread_join(3) is a much more reasonable choice here. You'd do something like:
int join_res = pthread_join(thread1, NULL);
if (join_res != 0) {
fprintf(stderr, "pthread_join(3) error: %s\n", strerror(join_res));
exit(EXIT_FAILURE);
}
Inside thread_read_file(), you probably want pthread_exit(3) when handling errors instead of exit(2), since the latter will terminate the entire process, not just the local thread. You also need to handle malloc(3) errors.
Here's the code with all of these issues addressed:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <pthread.h>
#define content_file "/home/tias/content.txt" //this file contains "foobar!!"
typedef struct {
int reading; // 0 = not reading , 1 = reading , 2 = finished reading
char *content; // content of the file
char *file; // file to read
} struct_file_content;
struct_file_content first_file;
void *thread_read_file(void *data) {
struct_file_content *thisdata = data;
long length;
char *thiscontent = NULL;
fprintf(stdout,"thread_Read_file called with file: %s and reading: %u\n", thisdata->file, thisdata->reading);
FILE *f = fopen (thisdata->file, "r");
if (f) {
fseek(f, 0, SEEK_END);
length = ftell(f);
fseek (f, 0, SEEK_SET);
if (length > 39) {
fprintf(stderr,"file %s is too big\n", thisdata->file);
pthread_exit(NULL);
}
thiscontent = malloc(length);
if (thiscontent) {
fread(thiscontent, 1, length, f);
} else {
perror("malloc(3) error");
pthread_exit(NULL);
}
fclose(f);
thisdata->content = thiscontent;
} else {
fprintf(stderr, "cannot open file %s\n", thisdata->file);
pthread_exit(NULL);
}
thisdata->reading = 2;
fprintf(stdout, "finished reading: %u\n", thisdata->reading);
fprintf(stdout, "content: %s\n", thiscontent);
return NULL;
}
int main(void) {
first_file.reading = 1;
first_file.content = NULL;
first_file.file = content_file;
pthread_t thread1;
int thread_res = pthread_create(&thread1, NULL, thread_read_file, &first_file);
if (thread_res != 0) {
fprintf(stderr, "pthread_create(3) error: %s\n", strerror(thread_res));
exit(EXIT_FAILURE);
}
int join_res = pthread_join(thread1, NULL);
if (join_res != 0) {
fprintf(stderr, "pthread_join(3) error: %s\n", strerror(join_res));
exit(EXIT_FAILURE);
}
fprintf(stdout, "Read file %s, reading: %u, content: %s\n", first_file.file, first_file.reading, first_file.content);
return 0;
}
UPDATE
From the comments, it seems like you want to do some additional processing and periodically test (at your convenience) whether the thread is done reading. Your approach of using a flag to test for termination is mostly correct, but you should synchronize access to the reading field of struct_file_content to make sure that you always get consistent values. As such, I suggest adding a mutex to struct_file_content that is used to control concurrent access to the reading field. You should lock the mutex every time you need to read or update reading.
So, the structure definition becomes:
typedef struct {
pthread_mutex_t read_mutex; // synchronize access to reading flag
int reading; // 0 = not reading , 1 = reading , 2 = finished reading
char *content; // content of the file
char *file; // file to read
} struct_file_content;
Then, as part of initializing struct_file_content, you need to remember to initialize the mutex. Here's how you'd do it in main():
int mutex_err = pthread_mutex_init(&first_file.read_mutex, NULL);
if (mutex_err != 0) {
fprintf(stderr, "pthread_mutex_init(3) error: %s\n", strerror(mutex_err));
exit(EXIT_FAILURE);
}
first_file.reading = 1;
first_file.content = NULL;
first_file.file = content_file;
Now, the loop in main() simply locks the mutex, checks the status of the reading field (breaking out if it is equal to 2), and unlocks the mutex. Something like:
int read_done = 0;
while (!read_done) {
mutex_err = pthread_mutex_lock(&first_file.read_mutex);
if (mutex_err != 0) {
fprintf(stderr, "pthread_mutex_lock(3) error: %s\n", strerror(mutex_err));
exit(EXIT_FAILURE);
}
/* Reading is finished when first_file.reading == 2 */
read_done = (first_file.reading == 2);
if (first_file.reading != 2)
printf("Still reading, reading: %u\n", first_file.reading);
mutex_err = pthread_mutex_unlock(&first_file.read_mutex);
if (mutex_err != 0) {
fprintf(stderr, "pthread_mutex_unlock(3) error: %s\n", strerror(mutex_err));
}
}
Of course, you also need to update the thread function to lock the mutex before modifying reading:
void *thread_read_file(void *data) {
struct_file_content *thisdata = data;
int mutex_res;
long length;
char *thiscontent = NULL;
mutex_res = pthread_mutex_lock(&thisdata->read_mutex);
if (mutex_res != 0) {
fprintf(stderr, "thread_read_file() failed to acquire mutex: %s\n", strerror(mutex_res));
pthread_exit(NULL);
}
fprintf(stdout, "thread_read_file() called with file: %s and reading: %u\n", thisdata->file, thisdata->reading);
mutex_res = pthread_mutex_unlock(&thisdata->read_mutex);
if (mutex_res != 0) {
fprintf(stderr, "thread_read_file() failed to release mutex: %s\n", strerror(mutex_res));
pthread_exit(NULL);
}
FILE *f = fopen(thisdata->file, "r");
if (f) {
fseek(f, 0, SEEK_END);
length = ftell(f);
fseek (f, 0, SEEK_SET);
if (length > 39) {
fprintf(stderr, "file %s is too big\n", thisdata->file);
pthread_exit(NULL);
}
thiscontent = malloc(length);
if (thiscontent) {
fread(thiscontent, 1, length, f);
} else {
perror("malloc(3) error");
pthread_exit(NULL);
}
fclose(f);
thisdata->content = thiscontent;
} else {
fprintf(stderr, "cannot open file %s\n", thisdata->file);
pthread_exit(NULL);
}
mutex_res = pthread_mutex_lock(&thisdata->read_mutex);
if (mutex_res != 0) {
fprintf(stderr, "thread_read_file() failed to acquire mutex: %s\n", strerror(mutex_res));
pthread_exit(NULL);
}
thisdata->reading = 2;
fprintf(stdout, "finished reading: %u\n", thisdata->reading);
mutex_res = pthread_mutex_unlock(&thisdata->read_mutex);
if (mutex_res != 0) {
fprintf(stderr, "thread_read_file() failed to release mutex: %s\n", strerror(mutex_res));
pthread_exit(NULL);
}
fprintf(stdout, "content: %s\n", thiscontent);
return NULL;
}
That should be enough. Here's the full code:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <pthread.h>
#define content_file "/home/tias/content.txt" //this file contains "foobar!!"
typedef struct {
pthread_mutex_t read_mutex; // synchronize access to reading flag
int reading; // 0 = not reading , 1 = reading , 2 = finished reading
char *content; // content of the file
char *file; // file to read
} struct_file_content;
struct_file_content first_file;
void *thread_read_file(void *data) {
struct_file_content *thisdata = data;
int mutex_res;
long length;
char *thiscontent = NULL;
mutex_res = pthread_mutex_lock(&thisdata->read_mutex);
if (mutex_res != 0) {
fprintf(stderr, "thread_read_file() failed to acquire mutex: %s\n", strerror(mutex_res));
pthread_exit(NULL);
}
fprintf(stdout, "thread_read_file() called with file: %s and reading: %u\n", thisdata->file, thisdata->reading);
mutex_res = pthread_mutex_unlock(&thisdata->read_mutex);
if (mutex_res != 0) {
fprintf(stderr, "thread_read_file() failed to release mutex: %s\n", strerror(mutex_res));
pthread_exit(NULL);
}
FILE *f = fopen(thisdata->file, "r");
if (f) {
fseek(f, 0, SEEK_END);
length = ftell(f);
fseek (f, 0, SEEK_SET);
if (length > 39) {
fprintf(stderr, "file %s is too big\n", thisdata->file);
pthread_exit(NULL);
}
thiscontent = malloc(length);
if (thiscontent) {
fread(thiscontent, 1, length, f);
} else {
perror("malloc(3) error");
pthread_exit(NULL);
}
fclose(f);
thisdata->content = thiscontent;
} else {
fprintf(stderr, "cannot open file %s\n", thisdata->file);
pthread_exit(NULL);
}
mutex_res = pthread_mutex_lock(&thisdata->read_mutex);
if (mutex_res != 0) {
fprintf(stderr, "thread_read_file() failed to acquire mutex: %s\n", strerror(mutex_res));
pthread_exit(NULL);
}
thisdata->reading = 2;
fprintf(stdout, "finished reading: %u\n", thisdata->reading);
mutex_res = pthread_mutex_unlock(&thisdata->read_mutex);
if (mutex_res != 0) {
fprintf(stderr, "thread_read_file() failed to release mutex: %s\n", strerror(mutex_res));
pthread_exit(NULL);
}
fprintf(stdout, "content: %s\n", thiscontent);
return NULL;
}
int main(void) {
int mutex_err = pthread_mutex_init(&first_file.read_mutex, NULL);
if (mutex_err != 0) {
fprintf(stderr, "pthread_mutex_init(3) error: %s\n", strerror(mutex_err));
exit(EXIT_FAILURE);
}
first_file.reading = 1;
first_file.content = NULL;
first_file.file = content_file;
pthread_t thread1;
int thread_res = pthread_create(&thread1, NULL, thread_read_file, &first_file);
if (thread_res != 0) {
fprintf(stderr, "pthread_create(3) error: %s\n", strerror(thread_res));
exit(EXIT_FAILURE);
}
int read_done = 0;
while (!read_done) {
mutex_err = pthread_mutex_lock(&first_file.read_mutex);
if (mutex_err != 0) {
fprintf(stderr, "pthread_mutex_lock(3) error: %s\n", strerror(mutex_err));
exit(EXIT_FAILURE);
}
/* Reading is finished when first_file.reading == 2 */
read_done = (first_file.reading == 2);
if (first_file.reading != 2)
printf("Still reading, reading: %u\n", first_file.reading);
mutex_err = pthread_mutex_unlock(&first_file.read_mutex);
if (mutex_err != 0) {
fprintf(stderr, "pthread_mutex_unlock(3) error: %s\n", strerror(mutex_err));
}
}
/* Here we don't need to lock because the thread has finished and no other thread is
* using this struct
*/
fprintf(stdout, "Read file %s, reading: %u, content: %s\n", first_file.file, first_file.reading, first_file.content);
free(first_file.content);
mutex_err = pthread_mutex_destroy(&first_file.read_mutex);
if (mutex_err != 0) {
fprintf(stderr, "Warning: Error destroying mutex: %s\n", strerror(mutex_err));
}
return 0;
}
Note that I added cleanup code in the end of main(). Even though it is not necessary (because the program is about to terminate), it is there to make sure you don't forget what kind of cleanup needs to be done once a thread terminates.
I am New to audio programming.I want to create small application which is capable of playing and gives volume control . I am using alsa-lib.
I want to know what is the purpose of switch (ex.Master Playback switch), enum in mixer elements and what value should i set to those switchs .
Please suggest me some tutorial for mixer settings as well as alsa programming .
Just collecting some here, that have example code:
ALSA Programming HOWTO v.1.0.0 [alsamodular.sourceforge.net]
A tutorial on using the ALSA Audio API [equalarea.com] 2002
A close look at ALSA [volkerschatz.com]
ALSA API - Sample Programs With Source Code By Aquiles Yanez 2005
Introduction to Sound Programming with ALSA | Linux Journal (pg3 with example code) 2004
Note that some of these are old, and API may have changed in the meantime... you can also look up aplay.c (the source for the command line arecord and aplay), but that one is not the easiest to read for starters...
You'll have a tough time finding anything concrete on ALSA, as I have have found from just starting learning it too. The best place to begin is the ALSA project homepage where they link to a number of tutorials, the best one being Dr Nagorni's one IMO.
From what it sounds like you're trying to do, JACK would most likely be a quicker and easier solution, though.
Check out the docs. There are some good examples.
http://www.alsa-project.org/alsa-doc/alsa-lib/examples.html
Be aware of the safe alsa subset.
https://www.winehq.org/pipermail/wine-bugs/2009-June/179698.html
Here's something small I put together using the various sources I could find. It miiiiiiiiiight be a good starting point.
/* Compile with gcc -lasound -pthread threadaudio.c */
#include <alsa/asoundlib.h>
#include <pthread.h>
#include <stdio.h>
unsigned char audiobuffer[0x400];
pthread_mutex_t audiomutex = PTHREAD_MUTEX_INITIALIZER;
void changeaudio (int volume) {
int i;
pthread_mutex_lock(&audiomutex);
for (i = 0; i < sizeof(audiobuffer); i++)
audiobuffer[i] = (random() & 0xff) * volume / 10;
pthread_mutex_unlock(&audiomutex);
}
void *startaudio (void *param)
{
static char *device = "default";
snd_output_t *output = NULL;
int *audiostop = (int*)param;
int err;
snd_pcm_t *handle;
snd_pcm_sframes_t frames;
changeaudio(5);
if ((err = snd_pcm_open(&handle, device, SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
printf("Playback open error: %s\n", snd_strerror(err));
exit(EXIT_FAILURE);
}
if ((err = snd_pcm_set_params(handle,
SND_PCM_FORMAT_U8,
SND_PCM_ACCESS_RW_INTERLEAVED,
1,
48000,
1,
100000)) < 0) { /* 0.1sec */
printf("Playback open error: %s\n", snd_strerror(err));
exit(EXIT_FAILURE);
}
while (!*audiostop) {
err = snd_pcm_wait(handle, 1000);
if (err < 0) {
fprintf (stderr, "poll failed (%d)\n", err);
break;
}
pthread_mutex_lock(&audiomutex);
frames = snd_pcm_writei(handle, audiobuffer, sizeof(audiobuffer));
pthread_mutex_unlock(&audiomutex);
if (frames < 0)
err = snd_pcm_recover(handle, frames, 0);
if (err < 0) {
printf("snd_pcm_writei failed: %s\n", snd_strerror(err));
break;
}
if (frames > 0 && frames < (long)sizeof(audiobuffer))
printf("Short write (expected %li, wrote %li)\n", (long)sizeof(audiobuffer), frames);
}
snd_pcm_close(handle);
}
int main(void)
{
pthread_t audiothread;
int audiostop = 0;
int volume;
pthread_create(&audiothread, NULL, startaudio, &audiostop);
while (1) {
printf("Enter volume 1 through 10. [0 to quit.]: ");
scanf("%d", &volume);
if (volume == 0) break;
changeaudio(volume);
}
audiostop = 1;
pthread_join(audiothread, NULL);
return 0;
}
And after reading the code above you'll probably want to read this article regarding (among other things) not using locks.
http://www.rossbencina.com/code/real-time-audio-programming-101-time-waits-for-nothing