From: Rich Felker <dalias@libc.org>
To: musl@lists.openwall.com
Subject: Re: [PATCH 4/8] determine the existence of private futexes at the first thread creation
Date: Sat, 24 Jun 2017 18:23:38 -0400 [thread overview]
Message-ID: <20170624222338.GX1627@brightrain.aerifal.cx> (raw)
In-Reply-To: <f21ea165c38a4dfc9ac0b9a5b95f2a5622697213.1498228733.git.Jens.Gustedt@inria.fr>
On Tue, Jun 20, 2017 at 10:35:28PM +0200, Jens Gustedt wrote:
> diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
> index ca5c6b90..26945022 100644
> --- a/src/thread/pthread_create.c
> +++ b/src/thread/pthread_create.c
> @@ -10,6 +10,8 @@ void *__mmap(void *, size_t, int, int, int, off_t);
> int __munmap(void *, size_t);
> int __mprotect(void *, size_t, int);
>
> +int __futex_private = 0;
> +
> static void dummy_0()
> {
> }
> @@ -277,7 +279,13 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att
> new->unblock_cancel = self->cancel;
> new->CANARY = self->CANARY;
>
> - a_inc(&libc.threads_minus_1);
> + if (!a_fetch_add(&libc.threads_minus_1, 1)) {
> + // As long as we only have one thread, test if this supports
> + // private futexes.
> + __lock_t dummy = { 0 };
> + if (__syscall(SYS_futex, dummy.lc, FUTEX_WAKE|FUTEX_PRIVATE, 0) != -ENOSYS)
> + __futex_private = FUTEX_PRIVATE;
> + }
> ret = __clone((c11 ? start_c11 : start), stack, flags, new, &new->tid, TP_ADJ(new), &new->tid);
For future reference, this is also the wrong way to do "on first
thread creation" -- it will trigger every time the number of threads
changes from 1 to 2. There's already a block at the top of the
function for first thread creation, that sets up stdio for
multithreaded use and such; that would be the place to put this.
I was also momentarily concerned about whether there are cases where a
single-threaded process needs to be able to use the futex ops, but I
think it probably doesn't matter except for the not-private case
(pshared sync objects).
Rich
next prev parent reply other threads:[~2017-06-24 22:23 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-23 14:38 [PATCH 0/8] the new __lock and follow up patches Jens Gustedt
2017-06-16 7:11 ` [PATCH 1/8] (V2) a new lock algorithm with lock value and CS counts in the same atomic int Jens Gustedt
2017-12-20 21:58 ` Rich Felker
2017-12-21 11:06 ` Jens Gustedt
2017-12-21 23:34 ` Rich Felker
2018-01-03 14:08 ` automated coding style Jens Gustedt
2018-01-11 4:41 ` Samuel Holland
2018-01-11 8:28 ` Jens Gustedt
2017-06-20 13:25 ` [PATCH 3/8] revise the definition of multiple basic locks in the code Jens Gustedt
2017-06-20 19:08 ` [PATCH 6/8] use the new lock algorithm for malloc Jens Gustedt
2017-06-23 15:01 ` Jens Gustedt
2017-06-20 19:41 ` [PATCH 2/8] consistently use the LOCK an UNLOCK macros Jens Gustedt
2017-06-20 19:44 ` [PATCH 5/8] separate the fast parts of __lock and __unlock into a .h file that may be used by other TU Jens Gustedt
2017-06-20 20:35 ` [PATCH 4/8] determine the existence of private futexes at the first thread creation Jens Gustedt
2017-06-23 17:05 ` Rich Felker
2017-06-23 17:16 ` Jens Gustedt
2017-06-23 21:48 ` Jens Gustedt
2017-06-23 22:08 ` Rich Felker
2017-06-23 23:42 ` Jens Gustedt
2017-06-24 0:53 ` Rich Felker
2017-06-24 8:00 ` Jens Gustedt
2017-06-24 10:12 ` flag 128 Jens Gustedt
2017-06-24 22:28 ` Rich Felker
2017-06-24 22:23 ` Rich Felker [this message]
2017-06-22 21:17 ` [PATCH 7/8] implement __unlock_requeue Jens Gustedt
2017-06-22 21:42 ` [PATCH 8/8] implement the local lock for conditions with __lock & Co Jens Gustedt
2017-06-23 14:57 ` [PATCH 0/8] the new __lock and follow up patches Jens Gustedt
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