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.TH GETTID 2 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
gettid \- get thread identification
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.PP
.B pid_t gettid(void);
.fi
.PP
.IR Note :
There is no glibc wrapper for this system call; see NOTES.
.SH DESCRIPTION
.BR gettid ()
returns the caller's thread ID (TID).
In a single-threaded process, the thread ID
is equal to the process ID (PID, as returned by
.BR getpid (2)).
In a multithreaded process, all threads
have the same PID, but each one has a unique TID.
For further details, see the discussion of
.BR CLONE_THREAD
in
.BR clone (2).
.SH RETURN VALUE
On success, returns the thread ID of the calling process.
.SH ERRORS
This call is always successful.
.SH VERSIONS
The
.BR gettid ()
system call first appeared on Linux in kernel 2.4.11.
.SH CONFORMING TO
.BR gettid ()
is Linux-specific and should not be used in programs that
are intended to be portable.
.SH NOTES
Glibc does not provide a wrapper for this system call; call it using
.BR syscall (2).
.\" FIXME . See http://sourceware.org/bugzilla/show_bug.cgi?id=6399
.\" "gettid() should have a wrapper"
.PP
The thread ID returned by this call is not the same thing as a
POSIX thread ID (i.e., the opaque value returned by
.BR pthread_self (3)).
.PP
In a new thread group created by a
.BR clone (2)
call that does not specify the
.BR CLONE_THREAD
flag (or, equivalently, a new process created by
.BR fork (2)),
the new process is a thread group leader,
and its thread group ID (the value returned by
.BR getpid (2))
is the same as its thread ID (the value returned by
.BR gettid ()).
.SH SEE ALSO
.BR capget (2),
.BR clone (2),
.BR fcntl (2),
.BR fork (2),
.BR getpid (2),
.BR get_robust_list (2),
.\" .BR kcmp (2),
.BR ioprio_set (2),
.\" .BR move_pages (2),
.\" .BR migrate_pages (2),
.BR perf_event_open (2),
.\" .BR process_vm_readv (2),
.\" .BR ptrace (2),
.BR sched_setaffinity (2),
.BR sched_setparam (2),
.BR sched_setscheduler (2),
.BR tgkill (2),
.BR timer_create (2)
.SH COLOPHON
This page is part of release 4.16 of the Linux
.I 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/.