1 .\" Copyright (C) 2008 Michael Kerrisk <tmk.manpages@gmail.com>
2 .\" and Copyright 2003 Abhijit Menon-Sen <ams@wiw.org>
4 .\" %%%LICENSE_START(VERBATIM)
5 .\" Permission is granted to make and distribute verbatim copies of this
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9 .\" Permission is granted to copy and distribute modified versions of this
10 .\" manual under the conditions for verbatim copying, provided that the
11 .\" entire resulting derived work is distributed under the terms of a
12 .\" permission notice identical to this one.
14 .\" Since the Linux kernel and libraries are constantly changing, this
15 .\" manual page may be incorrect or out-of-date. The author(s) assume no
16 .\" responsibility for errors or omissions, or for damages resulting from
17 .\" the use of the information contained herein. The author(s) may not
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19 .\" which is licensed free of charge, as they might when working
22 .\" Formatted or processed versions of this manual, if unaccompanied by
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26 .\" 2004-05-31, added tgkill, ahu, aeb
27 .\" 2008-01-15 mtk -- rewrote DESCRIPTION
29 .TH TKILL 2 2019-08-02 "Linux" "Linux Programmer's Manual"
31 tkill, tgkill \- send a signal to a thread
34 .BI "int tkill(int " tid ", int " sig );
36 .BI "int tgkill(int " tgid ", int " tid ", int " sig );
40 There is no glibc wrapper for
47 to the thread with the thread ID
53 can be used to send a signal only to a process (i.e., thread group)
54 as a whole, and the signal will be delivered to an arbitrary
55 thread within that process.)
58 is an obsolete predecessor to
60 It allows only the target thread ID to be specified,
61 which may result in the wrong thread being signaled if a thread
62 terminates and its thread ID is recycled.
63 Avoid using this system call.
64 .\" FIXME Maybe say something about the following:
65 .\" http://sourceware.org/bugzilla/show_bug.cgi?id=12889
67 .\" Quoting Rich Felker <bugdal@aerifal.cx>:
69 .\" There is a race condition in pthread_kill: it is possible that,
70 .\" between the time pthread_kill reads the pid/tid from the target
71 .\" thread descriptor and the time it makes the tgkill syscall,
72 .\" the target thread terminates and the same tid gets assigned
73 .\" to a new thread in the same process.
75 .\" (The tgkill syscall was designed to eliminate a similar race
76 .\" condition in tkill, but it only succeeded in eliminating races
77 .\" where the tid gets reused in a different process, and does not
78 .\" help if the same tid gets assigned to a new thread in the
81 .\" The only solution I can see is to introduce a mutex that ensures
82 .\" that a thread cannot exit while pthread_kill is being called on it.
84 .\" Note that in most real-world situations, like almost all race
85 .\" conditions, this one will be extremely rare. To make it
86 .\" measurable, one could exhaust all but 1-2 available pid values,
87 .\" possibly by lowering the max pid parameter in /proc, forcing
88 .\" the same tid to be reused rapidly.
90 These are the raw system call interfaces, meant for internal
93 On success, zero is returned.
94 On error, \-1 is returned, and \fIerrno\fP
101 resource limit was reached and
103 is a real-time signal.
106 Insufficient kernel memory was available and
108 is a real-time signal.
111 An invalid thread ID, thread group ID, or signal was specified.
115 For the required permissions, see
119 No process with the specified thread ID (and thread group ID) exists.
122 is supported since Linux 2.4.19 / 2.5.4.
124 was added in Linux 2.5.75.
128 was added to glibc in version 2.30.
133 are Linux-specific and should not be used
134 in programs that are intended to be portable.
136 See the description of
140 for an explanation of thread groups.
142 Glibc does not provide a wrapper for
146 Before glibc 2.30, there was also no wrapper function for
152 .BR rt_sigqueueinfo (2)