Duplicate call to pthread_join segvs

Duplicate call to pthread_join segvs

[Steve Osselton]

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Hi,

Am using musl on the latest Alpine Linux release. Although the behaviour of
calling pthread_join on
the same thread is undefined, would be nice if returned an errno as opposed
to a segv:

#include <pthread.h>

void * start_routine (void * arg)
{
}

int main (int argc, char ** argv)
{
  pthread_t id;

  pthread_create (&id, NULL, start_routine, NULL);
  pthread_join (id, NULL);
  pthread_join (id, NULL);
}

Cheers Steve.

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Re: Duplicate call to pthread_join segvs

[Rich Felker]

On Thu, Aug 18, 2016 at 12:51:23PM +0100, Steve Osselton wrote:
> Hi,
> 
> Am using musl on the latest Alpine Linux release. Although the behaviour of
> calling pthread_join on
> the same thread is undefined, would be nice if returned an errno as opposed
> to a segv:

No, that would be harmful because it would hide an extremely serious
bug (think what happens if another thread had been created after the
first join and its id happened to match the id of the already-joined
one). It would also be generally impossible to produce. pthread_join
is inherently a free-type operation (it frees a resource) and
double-frees are not reliably detectable unless the implementation
just never reuses freed resources at all (i.e. leak them).

Rich