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Date:	Fri, 9 Mar 2012 02:14:02 +0100
From:	Enrico Forestieri <forenr AT lyx DOT org>
To:	cygwin AT cygwin DOT com
Subject:	Forking a program in a thread
Message-ID:	<20120309011402.GA4704@GIOVE>
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I would like to point out a regression, seemingly introduced in 1.7.10.
If a program is exec'ed after forking in a thread and the program is
a native Windows program, it (seemingly) fails to start.

Please, find attached a test case. You can try it with gvim, for example.
There's no problem with the cygwin version of gvim:

$ ./fork_in_thread /usr/bin/gvim

but trying to start the native windows version:

$ ./fork_in_thread "/cygdrive/c/Program Files/Vim/vim73/gvim"

fails, in the sense that nothing happens and no error is reported.
A workaround here is using env. Indeed, the following works:

$ ./fork_in_thread env "/cygdrive/c/Program Files/Vim/vim73/gvim"

However, what puzzles me is the fact that a wrapper (like the one below)
starting gvim by using system() and compiled with i686-pc-mingw32-gcc
works, too!

All the previous examples were working in 1.7.9.

----- wrapper.c -----
#include <stdio.h>
int main(void)
{
    system("\"C:/Program Files/Vim/vim73/gvim\"");
    return 0;
}
---------------------

-- 
Enrico

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/*
 *    Forks a program in a thread.
 */ 
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>

void *start(void *arg)
{
    int pid, status;
    char **av = (char **)arg;
    printf("Forking in a thread to start %s\n", av[0]);
    pid = fork();
    if (pid == -1) {
	perror("fork");
	exit(1);
    }
    if (pid == 0) {
	execvp(av[0], av);
	perror("execvp");
	exit(1);
    }
    printf("Waiting in thread for %s to finish\n", av[0]);
    if (wait(&status) == -1) {
	perror("wait");
	exit(1);
    }
    if (WIFEXITED(status) && WEXITSTATUS(status))
	fprintf(stderr, "%s returned nonzero status %d", av[0], WEXITSTATUS(status));
    pthread_exit(NULL);
}

int main (int argc, char *argv[])
{
    pthread_t thread;
    int i, rc;
    char **av;

    if (argc < 2) {
        printf("Usage: %s <prog> [<arg> ...]\n", argv[0]);
        exit(0);
    }

    /* Build the argument vector for the child */
    av = malloc(argc * sizeof(char *));
    if (!av) {
        fprintf(stderr, "%s: no memory\n", argv[0]);
        exit(1);
    }
    for (i = 0; i < argc - 1; ++i) {
        av[i] = strdup(argv[i + 1]);
        if (!av[i]) {
	    fprintf(stderr, "%s: no memory\n", argv[0]);
	    exit(1);
        }
    }
    av[argc - 1] = NULL;

    printf("Main: creating thread for starting %s\n", argv[1]);
    rc = pthread_create(&thread, NULL, start, (void *)av);
    if (rc) {
        fprintf(stderr, "Error: return code from pthread_create() is %d\n", rc);
        exit(1);
    }
    return 0;
}


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