[vdr] Re: thread safeness II (was: Re: Re: solved: segment faultsfrom osdtelext plugin)

[Clemens Kirchgatterer <clemens@1541.org>]

Rainer Zocholl <UseNet-Posting-Nospam-74308-@zocki.toppoint.de> wrote:

>   static char *buffer = NULL;
>   const char *p = s;

[..]

>   return s; <======== is derivated from buffer, which is
>   "(re)malloced"
>             ( that will work every elegantly in single threading, but
>               in multithreading two tasks overwrites or invalidates
>               the memory of the other.)
> }
> 
> why is buffer "static" when it contains an malloc pointer?
> Is it it worth?

static is needed in this case. buffer would get lost between subsequent
calls to strescape otherwise. realloc on a NULL pointer is the same as
malloc and would produce a memleak.

> So why no mutex while using that buffer?

is the function called from multiple threads? if yes there should be a
mutex around it.

[..] many suspect functions


> Even if now it is absolutely clear for the programmer never to call
> that code from different tasks: There is nothing that will
> inhibit that "abuse", espacially in plugins.
> "But here it is working" does not proof anything in a multithreaded
> environemt. Here works also everthing. When i attach the debugger...
> The timing windows are so small that they may never occure on a slow
> machine(because the threads have never to sleep). 

full ack.

> Too the problem does not show up when it is caused.
> For example the above implicit "free" may release memory that is still
> pointed by a task which is sleeping for 24h hours.
> So the segfault may occure 24h later, but only if meanwhile nothing
> alloced memory in the same area. Then that third, totally unrelated 
> function may show "funny effects"...happy debugging...

i would like to hear a comment from klaus, if he is sure not to call any
of these functions with static locals from different threads.

clemens