posix man page for gettid

GETTID(2)						     Linux Programmer's Manual							 GETTID(2)

NAME
       gettid - get thread identification

SYNOPSIS
       #include <sys/types.h>

       pid_t gettid(void);

       Note: There is no glibc wrapper for this system call; see NOTES.

DESCRIPTION
       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
       getpid(2)).  In a multithreaded process, all threads have the same PID, but each one has a unique TID.  For further details, see  the  dis-
       cussion of CLONE_THREAD in clone(2).

RETURN VALUE
       On success, returns the thread ID of the calling process.

ERRORS
       This call is always successful.

VERSIONS
       The gettid() system call first appeared on Linux in kernel 2.4.11.

CONFORMING TO
       gettid() is Linux-specific and should not be used in programs that are intended to be portable.

NOTES
       Glibc does not provide a wrapper for this system call; call it using syscall(2).

       The thread ID returned by this call is not the same thing as a POSIX thread ID (i.e., the opaque value returned by pthread_self(3)).

       In  a  new  thread group created by a clone(2) call that does not specify the CLONE_THREAD flag (or, equivalently, a new process created by
       fork(2)), the new process is a thread group leader, and its thread group ID (the value returned by getpid(2)) is the same as its thread	ID
       (the value returned by gettid()).

SEE ALSO
       capget(2),  clone(2), fcntl(2), fork(2), getpid(2), get_robust_list(2), ioprio_set(2), perf_event_open(2), sched_setaffinity(2), sched_set-
       param(2), sched_setscheduler(2), tgkill(2), timer_create(2)

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								 GETTID(2)