[vlc-devel] [PATCH] Avoid deadlock on UDP stop
remi at remlab.net
Thu May 22 12:27:04 CEST 2014
Le 2014-05-22 18:00, Romain Vimont a écrit :
> However, (B ==> A) is false:
> By definition, we consider that we reach EOF once ThreadRead()
> put more blocks into to fifo queue anymore, i.e. once it calls
By definition, an UDP stream *never* reaches EOF. Setting EOF because
the user requested to stop is already a nasty kludge.
> The semantic of block_FifoWake() is to make
> exactly one call to block_FifoGet() nonblocking. During that call,
> fifo may not be empty (i.e. p_fifo->p_first != NULL). In that case,
> does not return NULL (and p_fifo->b_force_wake will remain unset).
By that line of reasoning, it is wrong to set EOF at all anyway. The
stream did not end. The user asked to stop reception.
> Therefore, setting b_eof when block_FifoGet() returns NULL is not
> sufficient, it would not fix the deadlock.
It will not fix the deadlock and your patch does not fix the alleged
deadlock either. Your patch is a kludge because not only it works around
the alleged bug rather than fix it, but it abuses the EOF flag.
> Instead, the command should be either "do not retrieve any block
> anymore" (what this patch implements), or "retrieve pending blocks,
> stop (do not block) once the queue is empty".
We already have an atomic variable for the purpose of detecting the
user stop. I refuse to add another one. Is it that difficult to grasp a
> I consider this as a root cause in itself.
We are going to have to disagree then.
If net_Read() failed, then there should not even be no more calls to
pf_block anyway. So either your alleged bug is non-existent or something
is wrong *outside* the UDP access.
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