Hi all,
Some days before I asked for a fork-like C-wrapper for clone() which
could be used like fork() thinking that somebody could have done it
before but I only received two e-mails saying that probably it
wasn't worth it or even it was complete non-sense.
Therefore, I've done it myself. Code follows.
Please, before beginning to flame me for doing "such kind of non-
standard threading model", I've to say that IMHO it has some merit.
After all it was E.W.Dijkstra who invented it in the late sixties.
Greetings from Barcelona
Francesc Oller
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/*
* Implementation of Dijkstra's parbegin/parend using clone()
* Modified from original Linus' clone.c example
* A proof of concept for academic purposes
* (c) Francesc Oller 2001, Linus Torvalds
* Under GPL license
*/
#include <unistd.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sched.h>
#include <linux/unistd.h>
#include "tinyx.h"
#define STACKSIZE 4096 /* 4 KB */
pid_t myclone(void)
{
long retval;
long *childsp;
register long * motherbp __asm__ ("%ebp");
/*
* allocate new stack for child
*/
childsp = malloc(STACKSIZE);
if (!childsp)
return -1;
childsp = (long *)(((char *)childsp) + STACKSIZE);
*--childsp = *(motherbp + 1); /* push return address */
*--childsp = *motherbp; /* push mother's bp */
/*
* Do clone() system call. We need to do the low-level stuff
* entirely in assembly as we're returning with a different
* stack in the child process and we couldn't otherwise guarantee
* that the program doesn't use the old stack incorrectly.
*
* Parameters to clone() system call:
* %eax - __NR_clone, clone system call number
* %ebx - clone_flags, bitmap of cloned data
* %ecx - new stack pointer for cloned child
*
* In this example %ebx is CLONE_VM | CLONE_FS | CLONE_FILES |
* CLONE_SIGHAND which shares as much as possible between parent
* and child. (We or in the signal to be sent on child termination
* into clone_flags: SIGCHLD makes the cloned process work like
* a "normal" unix child process)
*
* The clone() system call returns (in %eax) the pid of the newly
* cloned process to the mother, and 0 to the cloned process. If
* an error occurs, the return value will be the negative errno.
*
* Prior to the creation of the child process, we have stored
* return adress and caller's bp in child's stack. Child will
* restore caller's bp and jmp to the post-clone adress. The
* "_exit()" system call at the child's body end will terminate
* the child.
*/
__asm__ __volatile__(
"int $0x80\n\t" /* Linux/i386 system call */
"testl %0,%0\n\t" /* check return value */
"jne 1f\n\t" /* jump if mother */
"popl %%ebp\n\t" /* restore caller's bp */
"ret\n" /* jmp to return address */
"1:\t"
:"=a" (retval)
:"0" (__NR_clone),
"b" (CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | SIGCHLD),
"c" (childsp));
if (retval < 0) {
errno = -retval;
retval = -1;
}
return retval;
}
int show_same_vm;
int main()
{
int fd;
fd = open("/dev/null", O_RDWR);
if (fd < 0) {
perror("/dev/null");
exit(1);
}
printf("mother:\t fd = %d\n", fd);
show_same_vm = 10;
printf("mother:\t vm = %d\n", show_same_vm);
switch(myclone())
{
case -1: perror("clone"); exit(1);
case 0:
printf("child:\t fd = %d\n", fd);
show_same_vm = 5;
printf("child:\t vm = %d\n", show_same_vm);
close(fd);
_exit(0);
default:
sleep(1);
printf("mother:\t vm = %d\n", show_same_vm);
if (write(fd, "c", 1) < 0)
printf("mother:\t child closed our file descriptor\n");
}
/*
* The implementation of this construct is left as an exercise
* to the reader ;-)
*/
/*parbegin
altpar
printf("I'm thread 1\n");
parbegin
altpar
printf("I'm thread 4, child of thread 1\n");
altpar
printf("I'm thread 5, child of thread 1\n");
altpar
printf("I'm thread 6, child of thread 1\n");
parend
altpar
printf("I'm thread 2\n");
altpar
printf("I'm thread 3\n");
parend*/
return 0;
}
cut here -----------------------------
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This archive was generated by hypermail 2b29 : Mon Apr 30 2001 - 21:00:13 EST