SDL_OpenAudioDevice() causes nearly 100% CPU usage

nc-pv · March 12, 2018, 7:14pm

SDL 2.0.5, Linux.

I am wondering why after calling SDL_OpenAudioDevice() the program starts to consume nearly 100% of CPU time of one core.

Even this highly simplified program will make it:

gist.github.com

https://gist.github.com/vl-80/511943db52459890e30501aa0885a793

sdl_openaudiodevice.cpp

#include <chrono>
#include <iostream>
#include <thread>
#include <SDL2/SDL.h>

void callback( void *, Uint8 * stream, int len )
{
    memset( stream, 0, len );
}

This file has been truncated. show original

The Audio Device starts paused, it does not play anything. I did strace on one of the threads with 100% CPU usage and this is what I saw:

Trace of process 10070 - ./sdl_audio
getpid()                                = 10067
getpid()                                = 10067
getpid()                                = 10067
poll([{fd=3, events=POLLIN|POLLERR|POLLNVAL}], 1, -1) = 1 ([{fd=3, revents=POLLIN}])
getpid()                                = 10067
getpid()                                = 10067
getpid()                                = 10067
poll([{fd=3, events=POLLIN|POLLERR|POLLNVAL}], 1, -1) = 1 ([{fd=3, revents=POLLIN}])
getpid()                                = 10067
getpid()                                = 10067
getpid()                                = 10067
poll([{fd=3, events=POLLIN|POLLERR|POLLNVAL}], 1, -1) = 1 ([{fd=3, revents=POLLIN}])
getpid()                                = 10067
getpid()                                = 10067
getpid()                                = 10067
poll([{fd=3, events=POLLIN|POLLERR|POLLNVAL}], 1, -1) = 1 ([{fd=3, revents=POLLIN}])
getpid()                                = 10067
getpid()                                = 10067
getpid()                                = 10067
poll([{fd=3, events=POLLIN|POLLERR|POLLNVAL}], 1, -1) = 1 ([{fd=3, revents=POLLIN}])
getpid()                                = 10067
getpid()                                = 10067
futex(0x55b3d0e0e6f0, FUTEX_LOCK_PI_PRIVATE, NULL) = 0
getpid()                                = 10067
futex(0x55b3d0e0e6f0, FUTEX_UNLOCK_PI_PRIVATE) = 0
getpid()                                = 10067
getpid()                                = 10067
write(6, "W", 1)                        = 1
getpid()                                = 10067
getpid()                                = 10067
read(3, "xxxxxxxxxx", 10)               = 10
read(3, "xxxxxxx", 10)                  = 7
read(3, 0x7f1845272c9e, 10)             = -1 EAGAIN (Resource temporarily unavailable)
futex(0x55b3d0e0e6f0, FUTEX_UNLOCK_PI_PRIVATE) = 0
poll([{fd=3, events=POLLIN|POLLERR|POLLNVAL}], 1, 1000) = 1 ([{fd=3, revents=POLLIN}])
getpid()                                = 10067
getpid()                                = 10067
getpid()                                = 10067
poll([{fd=3, events=POLLIN|POLLERR|POLLNVAL}], 1, -1) = 1 ([{fd=3, revents=POLLIN}])
getpid()                                = 10067
getpid()                                = 10067
getpid()                                = 10067
poll([{fd=3, events=POLLIN|POLLERR|POLLNVAL}], 1, -1) = 1 ([{fd=3, revents=POLLIN}])
getpid()                                = 10067
getpid()                                = 10067
getpid()                                = 10067
poll([{fd=3, events=POLLIN|POLLERR|POLLNVAL}], 1, -1) = 1 ([{fd=3, revents=POLLIN}])
getpid()                                = 10067
getpid()                                = 10067
getpid()                                = 10067
poll([{fd=3, events=POLLIN|POLLERR|POLLNVAL}], 1, -1) = 1 ([{fd=3, revents=POLLIN}])
getpid()                                = 10067
getpid()                                = 10067

Is it normal that even idling audio subsystem consumes 100% of the CPU time of one core?