pthread_cleanup_push error

[petter wahlman]

Code to trigger the problem:
================================================================
#include <stdio.h>
#include <pthread.h>

static void thread_destructor(void *arg)
{
    printf("die!\n");
}

int main(int argc, const char *argv[])
{
    pthread_cleanup_push(thread_destructor, NULL);

    return 0;
}

Compiling results in the following errors:
================================================================
/tmp/ cc foo.c -Wall
foo.c: In function ‘main’:
foo.c:14: error: expected ‘while’ at end of input
foo.c:14: error: expected declaration or statement at end of input
foo.c:14: error: expected declaration or statement at end of input

The problem is obvious if you look at the code generated by the preprocessor:
('do { } while(0)' is not terminated with '} while(0)', but 'do {' )
================================================================
...
int main(int argc, char **argv)
{
    do { __pthread_unwind_buf_t __cancel_buf; void (*__cancel_routine) (void *) = (((void *)0)); void *__cancel_arg = (((void *)0)); int not_first_call = __sigsetjmp ((struct __jmp_buf_tag *) (void *) __cancel_buf.__cancel_jmp_buf, 0); if (__builtin_expect (not_first_call, 0)) { __cancel_routine (__cancel_arg); __pthread_unwind_next (&__cancel_buf); } __pthread_register_cancel (&__cancel_buf); do {;

    return 0;
}

The correct code should look similar to the following:
================================================================
#define pthread_cleanup_push(__thread_destructor, __arg) \
do { \
    __pthread_unwind_buf_t __cancel_buf; \
    void (*__cancel_routine) (void *) = (__thread_destructor); \
    void *__cancel_arg = (__arg); \
    int not_first_call = __sigsetjmp ((struct __jmp_buf_tag *) (void *) __cancel_buf.__cancel_jmp_buf, 0); \
    if (__builtin_expect (not_first_call, 0)) { \
        __cancel_routine (__cancel_arg); \
        __pthread_unwind_next (&__cancel_buf); \
    } \
    __pthread_register_cancel (&__cancel_buf); \
} while(0)

ProblemType: Bug
DistroRelease: Ubuntu 10.04
Package: libc6-dev 2.11.1-0ubuntu7
ProcVersionSignature: Ubuntu 2.6.31-17.54-generic
Uname: Linux 2.6.31-17-generic x86_64
Architecture: amd64
Date: Tue May 4 09:57:52 2010
InstallationMedia: Ubuntu 9.10 "Karmic Koala" - Release amd64 (20091027)
ProcEnviron:
 PATH=(custom, user)
 LANG=en_US.utf8
 SHELL=/bin/bash
SourcePackage: eglibc

[Josh Matthews (joshmatthews-gmail)]

Not a bug. A pthread_cleanup_push must be accompanied by a matching pthread_cleanup_pop. The macro definition contains an explanation:

/* Believe or not, the definitions of pthread_cleanup_push and
 * pthread_cleanup_pop below are correct. Posix states that these
 * can be implemented as macros that might introduce opening and
 * closing braces, and that using setjmp/longjmp/return/break/continue
 * between them results in undefined behaviour.
 *
 * And indeed, GLibc and other C libraries use a similar definition
 */
#define pthread_cleanup_push(routine, arg) \
    do { \
        __pthread_cleanup_t __cleanup; \
        __pthread_cleanup_push( &__cleanup, (routine), (arg) ); \

#define pthread_cleanup_pop(execute) \
        __pthread_cleanup_pop( &__cleanup, (execute)); \
    } while (0);