[Caml-list] Sys.command is broken on MacOS X

[Caml-list] Sys.command is broken on MacOS X

[Sébastien Carlier]

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The system(3) C library function is seriously broken on MacOS X.
It may return with an Interrupted System Call error before the child
process has finished its execution, leaving a zombie process.

The Ocaml function Sys.command uses the system(3) function,
and thus is broken too.  Active DVI is one of the applications greatly
impacted by this bug, but there may be others.

The attached patch, to be applied to the Ocaml compiler, provides a
working implementation of the system(3) function.  If an Ocaml
application uses Sys.command, and unexpectedly fails on MacOS X
with "Interrupted System Call" errors, you should apply this patch.

--
Sébastien Carlier


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Index: byterun/sys.c
===================================================================
RCS file: /caml/ocaml/byterun/sys.c,v
retrieving revision 1.59
diff -r1.59 sys.c
256a257,298
> #if defined(SYS_rhapsody)
> int rhapsody_system(const char *string) {
>     int old_sigmask;
>     pid_t pid;
> 
>     if (string == 0)
> 	return 1;
>     old_sigmask = sigblock(sigmask(SIGQUIT));
>     pid = vfork();
>     if (pid < 0) {
> 	/* vfork failed */
> 	sigsetmask(old_sigmask);
> 	return -1;
>     } else if (pid == 0) {
> 	/* We are in the child process */
> 	sigsetmask(old_sigmask);
> 	execl("/bin/sh", "sh", "-c", string, 0);
> 	_exit(127);
> 	return -1;
>     } else {
> 	/* We are in the parent process */
> 	int status = 0;
> 	void* old_sigint;
> 	void* old_sigquit;
> 	int result;
> 
> 	old_sigint = signal(SIGINT, 0);
> 	old_sigquit = signal(SIGQUIT, 0);
> 	do {
> 	    result = waitpid(pid, &status, 0);
> 	} while (result < 0 && errno == EINTR);
> 	signal(SIGINT, old_sigint);
> 	signal(SIGQUIT, old_sigquit);
> 	sigsetmask(old_sigmask);
> 	if (result < 0)
> 	    return -1;
> 	else
> 	    return status;
>     }
> }
> #endif
> 
262a305,307
> #if defined(SYS_rhapsody)
>   status = rhapsody_system(String_val(command));
> #else
263a309
> #endif

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