From: "Mihai Donțu" <mihai.dontu@gmail.com>
To: Xin Tong <xerox.time.tech@gmail.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: futex system call in write
Date: Sun, 3 Jun 2012 12:16:03 +0300 [thread overview]
Message-ID: <20120603121603.047c86c4@mdontu-l> (raw)
In-Reply-To: <CALKntY1xQ7v5VRKxqT3A3G+W3s3CK_JtqWB5GkBcN08J6Hn=-A@mail.gmail.com>
On Sun, 3 Jun 2012 01:58:55 -0400 Xin Tong wrote:
> I am a program with 2 threads, each of which calling printf in a loop.
> when i strace this programs. i see besides write() gets calls a good
> number of times. futex gets call many times as well. it seems to be
> related to the write system call ? how is the futex system call used
> here ? maybe write() is blocking and futex is used to wait the thread
> up when the write finishes ? if that is the case, what about other
> blocking system calls ?
>
You should probably ask this question on a glibc mailing list.
What you're seeing is the effect of using the locking version of the
standard IO calls, where before each output a mutex is acquired to
ensure thread safety. Thus futex() has nothing to do with write(), it
is merely the underlaying system call for pthread_mutex_xxxx() calls.
--
Mihai Donțu
prev parent reply other threads:[~2012-06-03 9:16 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-03 5:58 futex system call in write Xin Tong
2012-06-03 9:16 ` Mihai Donțu [this message]
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