Re: snap-2004-11-03 breakage

[Ross Johnson <rpj at ise dot canberra dot edu dot au>]

Hi,

I definitely don't want to break applications unnecessarily and 
particularly applications that have been ported to several different 
POSIX systems, but on the other hand POSIX thread IDs are not required 
to be scalar. See the rationale from the definition of pthread_equal() 
in the Single Unix Specification version 3, which says:


       RATIONALE

   Implementations may choose to define a thread ID as a structure.
   This allows additional flexibility and robustness over using an
   *int*. For example, a thread ID could include a sequence number that
   allows detection of "dangling IDs" (copies of a thread ID that has
   been detached). Since the C language does not support comparison on
   structure types, the /pthread_equal/() function is provided to
   compare thread IDs.

I don't think this is new to SUS or SUS version 3 either.

Nor (given the above) does the value 0 (zero) for a thread ID have any 
special meaning in the standard, although it obviously does as the value 
returned by ec_thread_getpid() in ettercap. If you want to test if a 
thread exists given it's thread ID, use:

   if (pthread_kill(pid, 0) == 0)  /* or (... != ESRCH) */

That should be portable to all POSIX implementations.

I'm not dismissing your problem, but in this case I think it would be 
better to fix the application.

Regards.
Ross

Gisle Vanem wrote:

> snap-2004-11-03 breaks a lot of applications by the way 'pthread_t' is 
> defined:
>
> typedef struct {
>    void * p;                   /* Pointer to actual object */
>    unsigned int x;             /* Extra information - reuse count etc */
> } ptw32_handle_t;
>
> typedef ptw32_handle_t pthread_t;
>
> Code like (from Ettercap)
>  pthread_t pid = ec_thread_getpid("golem");
>  if (pid != 0)
>    ec_thread_destroy(pid);
>
> no longer works; you cannot compare a struct against 0.
>
> I'm not sure you really meant to do that or if the typedef should be
> typedef ptw32_handle_t *pthread_t;
>
> --gv