1/* System-specific extensions of <unistd.h>, Linux version. 
2 Copyright (C) 2019-2020 Free Software Foundation, Inc. 
3 This file is part of the GNU C Library. 
4 
5 The GNU C Library is free software; you can redistribute it and/or 
6 modify it under the terms of the GNU Lesser General Public 
7 License as published by the Free Software Foundation; either 
8 version 2.1 of the License, or (at your option) any later version. 
9 
10 The GNU C Library is distributed in the hope that it will be useful, 
11 but WITHOUT ANY WARRANTY; without even the implied warranty of 
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 
13 Lesser General Public License for more details. 
14 
15 You should have received a copy of the GNU Lesser General Public 
16 License along with the GNU C Library; if not, see 
17 <https://www.gnu.org/licenses/>. */ 
18 
19#ifndef _UNISTD_H 
20# error "Never include <bits/unistd_ext.h> directly; use <unistd.h> instead." 
21#endif 
22 
23#ifdef __USE_GNU 
24 
25/* Return the kernel thread ID (TID) of the current thread. The 
26 returned value is not subject to caching. Most Linux system calls 
27 accept a TID in place of a PID. Using the TID to change properties 
28 of a thread that has been created using pthread_create can lead to 
29 undefined behavior (comparable to manipulating file descriptors 
30 directly that have not been created explicitly). Note that a TID 
31 uniquely identifies a thread only while this thread is running; a 
32 TID can be reused once a thread has exited, even if the thread is 
33 not detached and has not been joined. */ 
34extern __pid_t gettid (void) __THROW; 
35 
36#endif 
37