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    SubjectRe: futex system call in write
    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
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