[Ffmpeg-devel] Stream file handle hijacking by another thread

[Stas Oskin]

Hi again.

>If you get this you obviously have not.
>You get this message only if the sum of threads executing one of either
>avcodec_open or avcodec_close is > 1.

I resolved the threading issues, but I'm still receiving errors from
av_write_frame(), and several threads are still writing to the same
file. After several debug sessions, I found the source of these
errors:

static int file_write(URLContext *h, unsigned char *buf, int size)
{
    int fd = (size_t)h->priv_data;
    return write(fd, buf, size);
}

Apparently, the h->priv_data somehow resets to 0x0, which in turn sets
the file descriptor to 0 as well. This leads to the mentioned errors,
and apparently to the bug of several threads writing to same file.

I also checked for errno messages:

Bad file descriptor - appears on the first write error
Operation not permitted - appears for any subsequent write error


I think this might be a threading bug in libavcodec, but it's weird it
got undetected so far. Any help to pinpoint the issue will be greatly
appreciated.