man2/gettid.2

   1 .\" Copyright 2003 Abhijit Menon-Sen <ams@wiw.org>
   2 .\" and Copyright (C) 2008 Michael Kerrisk <mtk.manpages@gmail.com>
   3 .\"
   4 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   5 .\"
   6 .TH GETTID 2 2021-03-22 "Linux" "Linux Programmer's Manual"
   7 .SH NAME
   8 gettid \- get thread identification
   9 .SH LIBRARY
  10 Standard C library
  11 .RI ( libc ", " \-lc )
  12 .SH SYNOPSIS
  13 .nf
  14 .B #define _GNU_SOURCE
  15 .B #include <unistd.h>
  16 .PP
  17 .B pid_t gettid(void);
  18 .fi
  19 .SH DESCRIPTION
  20 .BR gettid ()
  21 returns the caller's thread ID (TID).
  22 In a single-threaded process, the thread ID
  23 is equal to the process ID (PID, as returned by
  24 .BR getpid (2)).
  25 In a multithreaded process, all threads
  26 have the same PID, but each one has a unique TID.
  27 For further details, see the discussion of
  28 .B CLONE_THREAD
  29 in
  30 .BR clone (2).
  31 .SH RETURN VALUE
  32 On success, returns the thread ID of the calling thread.
  33 .SH ERRORS
  34 This call is always successful.
  35 .SH VERSIONS
  36 The
  37 .BR gettid ()
  38 system call first appeared on Linux in kernel 2.4.11.
  39 Library support was added in glibc 2.30.
  40 (Earlier glibc versions did not provide a wrapper for this system call,
  41 necessitating the use of
  42 .BR syscall (2).)
  43 .SH CONFORMING TO
  44 .BR gettid ()
  45 is Linux-specific and should not be used in programs that
  46 are intended to be portable.
  47 .SH NOTES
  48 The thread ID returned by this call is not the same thing as a
  49 POSIX thread ID (i.e., the opaque value returned by
  50 .BR pthread_self (3)).
  51 .PP
  52 In a new thread group created by a
  53 .BR clone (2)
  54 call that does not specify the
  55 .B CLONE_THREAD
  56 flag (or, equivalently, a new process created by
  57 .BR fork (2)),
  58 the new process is a thread group leader,
  59 and its thread group ID (the value returned by
  60 .BR getpid (2))
  61 is the same as its thread ID (the value returned by
  62 .BR gettid ()).
  63 .SH SEE ALSO
  64 .BR capget (2),
  65 .BR clone (2),
  66 .BR fcntl (2),
  67 .BR fork (2),
  68 .BR get_robust_list (2),
  69 .BR getpid (2),
  70 .\" .BR kcmp (2),
  71 .BR ioprio_set (2),
  72 .\" .BR move_pages (2),
  73 .\" .BR migrate_pages (2),
  74 .BR perf_event_open (2),
  75 .\" .BR process_vm_readv (2),
  76 .\" .BR ptrace (2),
  77 .BR sched_setaffinity (2),
  78 .BR sched_setparam (2),
  79 .BR sched_setscheduler (2),
  80 .BR tgkill (2),
  81 .BR timer_create (2)