calling pthread_self (on ubuntu), expensive? Post: 302427075

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Top Forums Programming calling pthread_self (on ubuntu), expensive? Post 302427075 by Corona688 on Thursday 3rd of June 2010 06:39:55 PM

06-03-2010

Registered User

The internals of this function are some pretty hairy inline assembly, differing wildly from architecture to architecture. I can't tell precisely what it's doing. But from the comments, it sure looks like they're trying hard to make it minimal(down to the instruction-level, even) and nonblocking.

Code:

/* Return the thread descriptor for the current thread.

   The contained asm must *not* be marked volatile since otherwise
   assignments like
        pthread_descr self = thread_self();
   do not get optimized away.  */
# define THREAD_SELF \
  ({ struct pthread *__self;                                                  \
     asm ("movq %%fs:%c1,%q0" : "=r" (__self)                                 \
          : "i" (offsetof (struct pthread, header.self)));                    \
     __self;})

Last edited by Corona688; 06-03-2010 at 07:46 PM..

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LEARN ABOUT OPENDARWIN

pthread_self

PTHREAD_SELF(3) 					     Linux Programmer's Manual						   PTHREAD_SELF(3)

NAME

       pthread_self - obtain ID of the calling thread

SYNOPSIS

       #include <pthread.h>

       pthread_t pthread_self(void);

       Compile and link with -pthread.

DESCRIPTION

       The  pthread_self()  function returns the ID of the calling thread.  This is the same value that is returned in *thread in the pthread_cre-
       ate(3) call that created this thread.

RETURN VALUE

       This function always succeeds, returning the calling thread's ID.

ERRORS

       This function always succeeds.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       +---------------+---------------+---------+
       |Interface      | Attribute     | Value	 |
       +---------------+---------------+---------+
       |pthread_self() | Thread safety | MT-Safe |
       +---------------+---------------+---------+
CONFORMING TO

       POSIX.1-2001, POSIX.1-2008.

NOTES

       POSIX.1 allows an implementation wide freedom in choosing the type used to represent a thread ID; for example, representation using  either
       an  arithmetic  type  or  a structure is permitted.  Therefore, variables of type pthread_t can't portably be compared using the C equality
       operator (==); use pthread_equal(3) instead.

       Thread identifiers should be considered opaque: any attempt to use a thread ID other than in pthreads calls is nonportable and can lead	to
       unspecified results.

       Thread  IDs  are  guaranteed to be unique only within a process.  A thread ID may be reused after a terminated thread has been joined, or a
       detached thread has terminated.

       The thread ID returned by pthread_self() is not the same thing as the kernel thread ID returned by a call to gettid(2).

SEE ALSO

       pthread_create(3), pthread_equal(3), pthreads(7)

COLOPHON

       This page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and  the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Linux								    2017-09-15							   PTHREAD_SELF(3)