USE_ATOMICS is only set if there is no thread implementation enabled, in
which case you can't expect any lock mechanism from FFmpeg.
This is also conflicting with the incoming use of stdatomic.
In such a case behave as if the buffer was not reallocatable -- allocate a
new one and copy the data (preserving just the part described by the
reference passed to av_buffer_realloc).
CC: libav-stable@libav.org
Reported-By: wm4 <nfxjfg@googlemail.com>
The buffer pool has to atomically add and remove entries from the linked
list of available buffers. This was done by removing the entire list
with a CAS operation, working on it, and then setting it back again
(using a retry-loop in case another thread was doing the same thing).
This could effectively cause memory leaks: while a thread was working on
the buffer list, other threads would allocate new buffers, increasing
the pool's total size. There was no real leak, but since these extra
buffers were not needed, but not free'd either (except when the buffer
pool was destroyed), this had the same effects as a real leak. For some
reason, growth was exponential, and could easily kill the process due
to OOM in real-world uses.
Fix this by using a mutex to protect the list operations. The fancy
way atomics remove the whole list to work on it is not needed anymore,
which also avoids the situation which was causing the leak.
Signed-off-by: Anton Khirnov <anton@khirnov.net>
new function allows to unref buffer and obtain its data.
Signed-off-by: Lukasz Marek <lukasz.m.luki@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
This race will always happen sooner or later in a multi-threaded
environment and it will over time lead to OOM.
This fix works by spinning, there are other ways by which this
can be fixed, like simply detecting the issue after it happened
and freeing the over-allocated memory or simply using a mutex.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Clément Bœsch
Anton Khirnov
Michael Niedermayer
wm4
Lukasz Marek
Stefano Sabatini
Xidorn Quan
Clément Bœsch