Poisoning returned buffers is based around the implicit assumption
that the contents of said buffers are transient. Yet this is not true
for the buffer pools used by the various hardware contexts which store
important state in there that needs to be preserved.
Furthermore, the current code is also based on the assumption
that the complete buffer pointed to by AVBuffer->data coincides with
AVBufferRef->data; yet an implementation might store some data of its
own before the actual user-visible data (accessible via AVBufferRef)
which would be broken by the current code.
(This is of course yet more proof that the AVBuffer API is not the right
tool for the hardware contexts.)
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Do this by putting an AVBuffer structure into BufferPoolEntry and
reuse it for all subsequent uses of said BufferPoolEntry.
Reviewed-by: James Almer <jamrial@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
No buffer will be fetched from the pool after it's uninitialized, so there's
no benefit from waiting until every single buffer has been returned to it
before freeing them all.
This should free some memory in certain scenarios, which can be beneficial in
low memory systems.
Based on a patch by Jonas Karlman.
Reviewed-by: Anton Khirnov <anton@khirnov.net>
Signed-off-by: James Almer <jamrial@gmail.com>
A common pattern e.g. in libavcodec is replacing/updating buffer
references: unref old one, ref new one. This function allows simplifying
such code and avoiding unnecessary refs+unrefs if the references are
already equivalent.
In order to access the original opaque parameter of a buffer in the buffer
pool. (The buffer pool implementation overrides the normal opaque parameter but
also saves it so it is accessible).
v2: add assertion check before dereferencing the BufferPoolEntry.
Signed-off-by: Marton Balint <cus@passwd.hu>
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>
Andreas Rheinhardt
James Almer
Anton Khirnov
Nicolas George
Marton Balint
Zhao Zhili
Clément Bœsch
Michael Niedermayer
wm4
Lukasz Marek
Stefano Sabatini
Xidorn Quan
Clément Bœsch