| .\" Copyright (C) 2008 Michael Kerrisk <tmk.manpages@gmail.com> |
| .\" and Copyright 2003 Abhijit Menon-Sen <ams@wiw.org> |
| .\" |
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| .\" 2004-05-31, added tgkill, ahu, aeb |
| .\" 2008-01-15 mtk -- rewrote DESCRIPTION |
| .\" |
| .TH TKILL 2 2021-03-22 "Linux" "Linux Programmer's Manual" |
| .SH NAME |
| tkill, tgkill \- send a signal to a thread |
| .SH SYNOPSIS |
| .nf |
| .BI "int tkill(pid_t " tid ", int " sig ); |
| .BI "int tgkill(pid_t " tgid ", pid_t " tid ", int " sig ); |
| .fi |
| .PP |
| .IR Note : |
| There is no glibc wrapper for |
| .BR tkill (); |
| see NOTES. |
| .SH DESCRIPTION |
| .BR tgkill () |
| sends the signal |
| .I sig |
| to the thread with the thread ID |
| .I tid |
| in the thread group |
| .IR tgid . |
| (By contrast, |
| .BR kill (2) |
| can be used to send a signal only to a process (i.e., thread group) |
| as a whole, and the signal will be delivered to an arbitrary |
| thread within that process.) |
| .PP |
| .BR tkill () |
| is an obsolete predecessor to |
| .BR tgkill (). |
| It allows only the target thread ID to be specified, |
| which may result in the wrong thread being signaled if a thread |
| terminates and its thread ID is recycled. |
| Avoid using this system call. |
| .\" FIXME Maybe say something about the following: |
| .\" http://sourceware.org/bugzilla/show_bug.cgi?id=12889 |
| .\" |
| .\" Quoting Rich Felker <bugdal@aerifal.cx>: |
| .\" |
| .\" There is a race condition in pthread_kill: it is possible that, |
| .\" between the time pthread_kill reads the pid/tid from the target |
| .\" thread descriptor and the time it makes the tgkill syscall, |
| .\" the target thread terminates and the same tid gets assigned |
| .\" to a new thread in the same process. |
| .\" |
| .\" (The tgkill syscall was designed to eliminate a similar race |
| .\" condition in tkill, but it only succeeded in eliminating races |
| .\" where the tid gets reused in a different process, and does not |
| .\" help if the same tid gets assigned to a new thread in the |
| .\" same process.) |
| .\" |
| .\" The only solution I can see is to introduce a mutex that ensures |
| .\" that a thread cannot exit while pthread_kill is being called on it. |
| .\" |
| .\" Note that in most real-world situations, like almost all race |
| .\" conditions, this one will be extremely rare. To make it |
| .\" measurable, one could exhaust all but 1-2 available pid values, |
| .\" possibly by lowering the max pid parameter in /proc, forcing |
| .\" the same tid to be reused rapidly. |
| .PP |
| These are the raw system call interfaces, meant for internal |
| thread library use. |
| .SH RETURN VALUE |
| On success, zero is returned. |
| On error, \-1 is returned, and \fIerrno\fP |
| is set to indicate the error. |
| .SH ERRORS |
| .TP |
| .B EAGAIN |
| The |
| .B RLIMIT_SIGPENDING |
| resource limit was reached and |
| .I sig |
| is a real-time signal. |
| .TP |
| .B EAGAIN |
| Insufficient kernel memory was available and |
| .I sig |
| is a real-time signal. |
| .TP |
| .B EINVAL |
| An invalid thread ID, thread group ID, or signal was specified. |
| .TP |
| .B EPERM |
| Permission denied. |
| For the required permissions, see |
| .BR kill (2). |
| .TP |
| .B ESRCH |
| No process with the specified thread ID (and thread group ID) exists. |
| .SH VERSIONS |
| .BR tkill () |
| is supported since Linux 2.4.19 / 2.5.4. |
| .BR tgkill () |
| was added in Linux 2.5.75. |
| .PP |
| Library support for |
| .BR tgkill () |
| was added to glibc in version 2.30. |
| .SH CONFORMING TO |
| .BR tkill () |
| and |
| .BR tgkill () |
| are Linux-specific and should not be used |
| in programs that are intended to be portable. |
| .SH NOTES |
| See the description of |
| .B CLONE_THREAD |
| in |
| .BR clone (2) |
| for an explanation of thread groups. |
| .PP |
| Glibc does not provide a wrapper for |
| .BR tkill (); |
| call it using |
| .BR syscall (2). |
| Before glibc 2.30, there was also no wrapper function for |
| .BR tgkill (). |
| .SH SEE ALSO |
| .BR clone (2), |
| .BR gettid (2), |
| .BR kill (2), |
| .BR rt_sigqueueinfo (2) |