compat/w32pthreads: change pthread_t into pointer to malloced struct

pthread_t is currently defined as a struct, which gets placed into
caller's memory and filled by pthread_create() (which accepts a
pthread_t*).

The problem with this approach is that pthread_join() accepts pthread_t
itself rather than a pointer to it, so it gets a _copy_ of this
structure. This causes non-deterministic failures of pthread_join() to
produce the correct return value - depending on whether the thread
already finished before pthread_join() is called (and thus the copy
contains the correct value), or not (then it contains 0).

Change the definition of pthread_t into a pointer to a struct, that gets
malloced by pthread_create() and freed by pthread_join().

Fixes random failures of fate-ffmpeg-error-rate-fail on Windows after
433cf391f58210432be907d817654929a66e80ba.

See also [1] for an alternative approach that does not require dynamic
allocation, but relies on an assumption that the pthread_t value
remains in a fixed memory location.

[1] https://code.videolan.org/videolan/x264/-/commit/23829dd2b2c909855481f46cc884b3c25d92c2d7

Reviewed-By: Martin Storsjö <martin@martin.st>

0 files changed, 0 insertions, 0 deletions