From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <f050e9670cf38f611b373308f56733df@proxima.alt.za>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] waitpid()
From: lucio@proxima.alt.za
In-Reply-To: <03be01c423aa$85426530$57d87d50@SOMA>
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Date: Fri, 16 Apr 2004 18:47:00 +0200
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> well i thought i'd coded it before.
> 
> look at pipe.c:

Thanks, Boyd, for the guidelines and also to Nemo for suggesting a
similar tack in previous private mail.

I have no idea whether this is adequate, but it matches some
superficial expectations, at least.

I'm including my efforts here because I'm going away for the weekend
and somebody may have the opportunity in the meantime to look at the
code and use it, but more specially to inspect it and hopefully make
suggestions on how to improve it (other than in code layout, I have a
great deal of trouble omitting spaces as seems to be the norm in Plan
9 sources, sorry about that).

I'll be grateful for all and any feedback, please be alerted that the
code is designed for use in the APE environment, modelled on the
NetBSD wait(2) man page I mentioned earlier.  It is intended to
replace

	/sys/src/ape/lib/ap/plan9/wait.c

in its entirety, but I have not checked this to any degree.  The
module compiles and runs with

	$ pcc -D_PLAN9_SOURCE -D_POSIX_SOURCE -I/sys/src/ape/lib/ap/plan9 -c pidwait.c
	$ 8l -o pidwait pidwait.8
	$ pidwait

from my home directory.

++L

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#include "lib.h"
#include <stdlib.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
#include "sys9.h"

pid_t wait(int *status);

pid_t waitpid(pid_t wpid, int *status, int options);

pid_t wait3(int *status, int options, Waitmsg *waitmsg);

pid_t wait4(pid_t wpid, int *status, int options, Waitmsg *waitmsg);

/*
**	PID cache
*/
typedef struct wdesc wdesc;
struct wdesc {
	pid_t w_pid;
	Waitmsg *w_msg;
	wdesc *w_next;
};
static wdesc *wd = 0;

static Waitmsg *
lookpid (pid_t pid) {
	wdesc **wp0 = &wd, *wp;
	Waitmsg *msg;

printf ("PID+ %d ", pid);

	if (pid == -1) {
		if (wd == 0)
			return 0;
		pid = wd->w_pid;
	}
	for (wp = wd; wp; wp = wp->w_next) {
printf ("looking: %d.", wp->w_pid);
		if (wp->w_pid == pid) {
			msg = wp->w_msg;
			*wp0 = wp->w_next;
printf (" yes\n");
			free (wp);
			return msg;
		}
		wp0 = &(wp->w_next);
	}
printf (" no\n");
	return 0;
}

static void
addpid (Waitmsg *msg) {
	wdesc **wp0 = &wd, *wp = malloc (sizeof (wdesc));

printf ("ADD: %d\n", msg->pid);
	wp->w_msg = msg;
	wp->w_pid = msg->pid;
	wp->w_next = wd;
	wd = wp;
}

pid_t
wait (int *status) {
	return wait4(-1, status, 0, 0);
}

pid_t
waitpid (pid_t wpid, int *status, int options) {
	return wait4(wpid, status, options, 0);
}

pid_t
wait3 (int *status, int options, Waitmsg *waitmsg) {
	return wait4(-1, status, options, waitmsg);
}

pid_t
wait4 (pid_t wpid, int *status, int options, Waitmsg *waitmsg) {
	Waitmsg *w;

	if (options & WNOHANG) {
		char pname[128];
		int i;
		struct stat buf;

		snprintf (pname, sizeof (pname), "/proc/%d/wait", getpid());
		i = stat (pname, &buf);
		if (i >= 0 && buf.st_size == 0)
			return 0;
	}
	if (w = lookpid (wpid)) {
		waitmsg = w;
		wpid = w->pid;
		return wpid;
	}
	w = _WAIT();
	while (w) {
		if (wpid <= 0) {
			waitmsg = w;
			wpid = w->pid;
			return wpid;
		}
		if (w->pid == wpid) {
			if (status) {
				int r = 0;
				int t = 0;
				char *bp, *ep;

				if (w->msg[0]) {
					/* message is 'prog pid:string' */
					bp = w->msg;
					while (*bp) {
						if (*bp++ == ':')
							break;
					}
					if (*bp == 0)
						bp = w->msg;
					r = strtol (bp, &ep, 10);
					if (*ep == 0) {
						if (r < 0 || r >= 256)
							r = 1;
					} else {
						t = _stringsig (bp);
						if (t == 0)
							r = 1;
					}
				}
				*status = (r << 8) | t;
			}
			waitmsg = w;
			wpid = w->pid;
			return wpid;
		} else {
			addpid (w);
		}
		w = _WAIT();
	}
	if (w == 0) {
		_syserrno ();
	}
}

#define N (5)

main () {
	int x, status;
	pid_t p, pid[N];
	Waitmsg waitmsg;

	for (x = 0; x < N; x++) {
		switch (pid[x] = fork()) {
			case 0:
				sleep (5);
				exit (0);
			case -1:
				_syserrno ();
				break;
			default:
				sleep (3);
				break;
		}
		printf ("ID[%d]: %d\n", x, pid[x]);
	}
	for (x = 0; x < N; x++) {
		if (p = wait4 (pid[x], &status, 0, &waitmsg))
			printf ("PID[%d]: %d\n", x, p);
	}
}
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