Because pthread failures are virtually undebuggable (which sure is
pretty strange, given all these heavy instrumentation tools these days).
Of course it affects only files which include osdep/threads.h.
I'm departing from the usual way to add symbols with config.h and using
"#if", and defining it on the compiler command line + "#ifdef" because I
don't want to include config.h from a header (which would be necessary
in this case) to keep things slightly cleaner. Maybe this is misguided,
but still.
This would have been easier if mpv defined its own wrappers for all
thread functions. But we don't (which to be honest is probably better
than e.g. going crazy like VLC and essentially reimplementing
everything). This seems to be a good compromise. Since it's off by
default and basically a developer tool, the minor undefined behavior
(redefining reserved symbols) isn't much of an issue.
There is not much of a reason to have these wrappers around. Use POSIX
standard functions directly, and use a separate utility function to take
care of the timespec calculations. (Course POSIX for using this weird
format for time values.)
Especially with other components (libavcodec, OSX stuff), the thread
list can get quite populated. Setting the thread name helps when
debugging.
Since this is not portable, we check the OS variants in waf configure.
old-configure just gets a special-case for glibc, since doing a full
check here would probably be a waste of effort.
Use the time as returned by mp_time_us() for mpthread_cond_timedwait(),
instead of calculating the struct timespec value based on a timeout.
This (probably) makes it easier to wait for a specific deadline.
This was part of osdep/threads.c out of laziness. But it doesn't contain
anything OS dependent. Note that the rest of threads.c actually isn't
all that OS dependent either (just some minor ifdeffery to work around
the lack of clock_gettime() on OSX).
Usually, you have to call pthread_cond_timedwait() in a loop (because it
can wake up sporadically). If this function is used by another higher
level function, which uses a relative timeout, we actually have to
reduce the timeout on each iteration - or, simpler, compute the
"deadline" at the beginning of the function, and always pass the same
absolute time to the waiting function.
Might be unsafe if the system time is changed. On the other hand, this
is a fundamental race condition with these APIs.
Kacper Michajłow
Thomas Weißschuh
wm4