From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <2b459c3d79844876c01956749cc7c35c@quintile.net>
From: "Steve Simon" <steve@quintile.net>
Date: Sat, 16 Dec 2006 14:55:24 +0000
To: 9fans@cse.psu.edu
Subject: Re: [9fans] wait race?
In-Reply-To: <ee9e417a0612151812r74d8e0b4ka955dc57509d523a@mail.gmail.com>
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>> for(i in `{seq 1 $n}){echo fu>/dev/null&}

> If you can reproduce the "hang", can you run ps and see if
> the pid that rc is waiting for.

I can reproduce this quite easily, with n=150,
one time in three the script hangs.

Waitfor seems to be waiting for a proc which has already exited.

felix% acid 63541
/proc/63541/text:386 plan 9 executable

/sys/lib/acid/port
/sys/lib/acid/386
acid: lstk()
await()+0x7 /sys/src/libc/9syscall/await.s:5
wait()+0x1b /sys/src/libc/9sys/wait.c:13
	buf=0x35323536
	fld=0xdfffcc04
	l=0x33930
	w=0x33938
Waitfor(pid=0xff7e)+0xb4 /sys/src/cmd/rc/plan9.c:210
	w=0x33938
	p=0x36538
	errbuf=0x33b4c
Xbackq()+0x158 /sys/src/cmd/rc/havefork.c:120
	wd=0x303531
	ewd=0xdfffeeef
	stop=0x1d958
	pfd=0x5
	f=0x33938
	s=0xdfffceef
	v=0x36538
	c=0xa
	pid=0xff7e
main(argc=0x1,argv=0xdfffefb4)+0x327 /sys/src/cmd/rc/exec.c:184
...

0xff7e == 65406

felix% ps
...
steve         63540    0:00   0:00      252K Await    rc
steve         63541    0:00   0:00      252K Await    rc
steve         63546    0:00   0:00      164K Pread    stats
steve         63547    0:00   0:00      168K Pread    stats
steve         63548    0:00   0:00      140K Pread    clock
steve         63549    0:00   0:00      140K Sleep    clock
steve         63550    0:00   0:00      376K Sleep    faces
steve         63551    0:00   0:00      376K Pread    faces
steve         63805    0:00   0:00     1116K Await    rio
steve         63806    0:00   0:00      252K Await    rc
steve         63807    0:00   0:00      124K Pread    nedmail
steve         63960    0:00   0:00     1116K Await    rio
steve         63961    0:00   0:00      252K Await    rc
steve         65153    0:00   0:00        8K Sleep    sleep
steve         65226    0:00   0:00     1116K Await    rio
steve         65227    0:00   0:00      252K Await    rc
steve         65228    0:00   0:00      228K Pread    sam
steve         65229    0:00   0:00      320K Rendez   samterm
steve         65230    0:00   0:00      320K Pread    samterm
steve         65231    0:00   0:00      320K Pread    samterm
steve         65232    0:00   0:00      320K Pread    samterm
steve         65233    0:00   0:00      320K Pread    samterm
steve         65251    0:00   0:00     1116K Await    rio
steve         65252    0:00   0:00      252K Await    rc
steve         65253    0:00   0:00      124K Pread    nedmail
steve         65419    0:00   0:00      200K Pread    ps
felix%