Use libasound's polling functions, implement a bridge to GSource /
GPollFD and send idle events to clients when an external program
changes the ALSA mixer volume.
After we've been hit by Large File Support problems several times in
the past week (which only occur on 32 bit platforms, which I don't
have), this is yet another attempt to fix the issue.
Added the "fd_util" library, which attempts to use the new thread-safe
Linux system calls pipe2(), accept4() and the options O_CLOEXEC,
SOCK_CLOEXEC. Without these, it falls back to FD_CLOEXEC, which is
not thread safe.
This is particularly important for the "pipe" output plugin (and
others, such as JACK/PulseAudio), because we were heavily leaking file
descriptors to child processes.
Don't let the mixer plugin "override" the libpulse callbacks.
Instead, add a "mixer" attribute to the pulse_output struct, and call
the mixer on all interesting events.
This is a complete rewrite of the PulseAudio output plugin. It uses
the asynchronous API, which gives us more control over everything.
Additionally, it connects to the PulseAudio server on startup, and
keeps this connection up while MPD runs. During pause, instead of
closing the stream, it enables "cork".
This mixer plugin may be used instead of the traditional global
software mixer. It integrates with the "volume" filter plugin, and
can control the software volume of an audio output which has no
hardware mixer.
Using two different kinds of locks may result in a race condition with
a deadlock. The libpulse callbacks need no locks at all, because the
mainloop object can be assumed to be already locked.
snd_config_update_free_global() frees cached ALSA configuration. This
keeps valgrind a little bit more quiet. This patch moves the call
from the open() method into the finish() method, which seems more
natural: it allows the use of the config cache, and improves the
cleanup phase.
There are numerous race conditions between the libpulse thread
(pulse_mixer.c callbacks) and the rest of MPD. Protect the volatile
attributes of the pulse_mixer struct with a mutex to fix that.
Don't mess with pulse_mixer.volume for setting the volume. This
variable should only be used to transfer the current volume from
sink_input_vol() to pulse_mixer_get_volume().
The pa_context_get_sink_input_info() function is asynchronous, and
after it returns, libpulse does not guarantee that the operation has
completed yet; in fact, it is not likely. Explicitly wait for the
operation to complete.
The code for the new pulse_wait_for_operation() function was inspired
by mplayer and xine code.
The pm->volume attribute was allocated in pulse_mixer_init(), but is
never freed. This leaks memory. Instead of adding the g_free() call
to pulse_mixer_finish(), let's just make "volume" a static attribute
of the pulse_mixer struct. That is easier to deal with.
Nobody needs to modify these strings. We can make them const, and
convert config_dup_block_string() to config_get_block_string(). This
also fixes memory leaks in the pulse mixer.
