cancellation handler won't run if pthread_exit called from C source instead of C++ source

Question

I'm linking a C++ source with a C source and a C++ source. I create a thread with pthread, a cancellation point and then I call pthread_exit either through the C or the C++ source file.

If the pthread_exit call comes from the C source, the cancellation handler does not fire! What may be the reason for this?

b.cc:

#include <cstdio>
#include <cstdlib>
#include <stdbool.h>
#include <pthread.h>


extern "C" void V();
extern "C" void Vpp();
extern "C" void Vs();

#define PTHREAD_EXIT Vs





void cleanup(void*v)
{
    fprintf(stderr, "Aadsfasdf\n");
    exit(0);
}


void* f(void*p)
{
    pthread_cleanup_push(cleanup, NULL);
    PTHREAD_EXIT();
    pthread_cleanup_pop(true);

    return NULL;
}

int main()
{
    pthread_t p;
    if (pthread_create(&p, NULL, f, NULL))
        abort();
    for(;;);
}

vpp.cc:

#include <pthread.h>

extern "C" void Vpp();
void Vpp() {
    pthread_exit(0);
}

v.c:

#include <pthread.h>

void V() {
    pthread_exit(0);
}

vs.s:

.text
Vs: .global Vs
    call pthread_exit
    spin: jmp spin

compilation with

g++ -c vpp.cc -g -o vpp.o -Wall
gcc -c v.c -g -o v.o -Wall
as vs.s -o vs.o
g++ b.cc vpp.o v.o vs.o -o b -lpthread -g -Wall

If PTHREAD_EXIT is Vpp the program displays a message and terminates, if it is V or Vs it doesn't.

the disassembly for V and Vpp is identical, and changing the definition of PTHREAD_EXIT between V and Vpp merely changes between call V and call Vpp in the disassembly.

EDIT: Not reproducible on another computer, so I guess I hit an error in the library or something.

Answer 1

I don't know, but you are giving the cancellation handler C++ linkage. What happens if you use C linkage for that as well?

extern "C"
{
  void cleanup(void*v) { ... }
}

Answer 2

In the "pthread.h" header file installed on my machine, the pthread_cleanup_push() function is not defined the same way for C and C++ (search for __cplusplus).

Could you try to give C linkage for both f() and cleanup()?

You may find the above link interesting: http://www.cs.rit.edu/~afb/20012/cs4/slides/threads-05.html

Answer 3

Inspired by Ch. Vu-Brugier I took a look at pthread.h and found out that I have to add

 #undef __EXCEPTIONS

before including pthread.h. This is a satisfactory workaround for my current needs.