Python or OS forking/threading problem?

[Florian Weimer]

"Neil Schemenauer" <nascheme at enme.ucalgary.ca> writes:

> Not for my problem on Linux.  My code didn't call sleep().  It
> may be a bug with the pthreads in libc6 for Linux.  I can't
> reproduce it with C code though.

I think I can explain what happens.  Look at the following code:

#include <stdio.h>
#include <string.h>

#include <unistd.h>
#include <pthread.h>

void *
thread(void * v)
{
  for (;;) {
    char buf[40];
    int len = sprintf(buf, "%lu\n", (unsigned long) getpid());
    write(1, buf, len);
    sleep(1);
  }
}

main()
{
  pthread_t t;
  pthread_create (&t, NULL, &thread, NULL);
  fork();
  sleep(3600);
}

This clearly shows that the thread is not duplicated on fork().  

Now look at the Python source code:

static PyObject *
posix_fork(self, args)
	PyObject *self;
	PyObject *args;
{
	int pid;
	if (!PyArg_ParseTuple(args, ":fork"))
		return NULL;
	pid = fork();
	if (pid == -1)
		return posix_error();
	PyOS_AfterFork();
	return PyInt_FromLong((long)pid);
}

void
PyOS_AfterFork()
{
#ifdef WITH_THREAD
	main_thread = PyThread_get_thread_ident();
	main_pid = getpid();
#endif
}

long PyThread_get_thread_ident _P0()
{
	volatile pthread_t threadid;
	if (!initialized)
		PyThread_init_thread();
	/* Jump through some hoops for Alpha OSF/1 */
	threadid = pthread_self();
	return (long) *(long *) &threadid;
}

In the child process, all threads have disappeared, but the code doesn't
seem to be prepared to handle this.