Date: Thu, 3 Dec 1998 20:56:35 -0500 (EST) From: HighWind Software Information <info@highwind.com> To: Kurt@OpenLDAP.Org Cc: current@FreeBSD.ORG Subject: Re: Thread fd locking and fork() Message-ID: <199812040156.UAA08468@highwind.com> In-Reply-To: <3.0.5.32.19981203124540.00b03b80@localhost> (Kurt@OpenLDAP.Org)
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In a Posix Threads environment, state of locks should not be changed.
If it's locked in the parent it must be locked in the child. Posix
Threads provides the pthread_atfork() function to allow the parent
to specify routines to manage fork()'ing... however it's not implemented
in FreeBSD. If it was, you could argue that -lc_r probably should push
an atfork cleanup handler.
Kurt,
1. I agree with you 100%. However, these locks are simply
libc_r internals and have nothing to do with locks the application can
see.
2. libc_r simply doesn't do the right thing with regard to these
internal fd locks in the case of fork().
3. My patch causes absolutely no harm and fixes the
problem. An atfork() handler will not work since it can't get inside
the libc_r library and no external calls exist to touch these hidden
libc_r private locks.
I've tested this and it works like a champ. If someone with commit
priv's could take a look at this simple code fragment for libc_r's
uthread_fork.c, I'd greatly appreciate it. It needs to be inserted
after fork() does its "kill all the threads but this one" thing.
/*
* Enter a loop to remove all locks on all locked fd's
*/
for (i = 0; i < _thread_dtablesize; i++) {
if (_thread_fd_table[i] != NULL) {
memset(&_thread_fd_table[i]->lock,
0, sizeof(_thread_fd_table[i]->lock));
_thread_fd_table[i]->r_owner = NULL;
_thread_fd_table[i]->w_owner = NULL;
_thread_fd_table[i]->r_fname = NULL;
_thread_fd_table[i]->w_fname = NULL;
_thread_fd_table[i]->r_lineno = 0;;
_thread_fd_table[i]->w_lineno = 0;;
_thread_fd_table[i]->r_lockcount = 0;
_thread_fd_table[i]->w_lockcount = 0;
/* Initialize the read/write queues: */
_thread_queue_init(&_thread_fd_table[i]->r_queu\
e);
_thread_queue_init(&_thread_fd_table[i]->w_queu\
e);
}
}
-Rob
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