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.\" Copyright (c) 2016 The FreeBSD Foundation, Inc.
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.\" Konstantin Belousov <kib@FreeBSD.org> under sponsorship
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.Dd May 5, 2020
.Dt THR_WAKE 2
.Os
.Sh NAME
.Nm thr_wake
.Nd wake up the suspended thread
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/thr.h
.Ft int
.Fn thr_wake "long id"
.Sh DESCRIPTION
.Bf -symbolic
This function is intended for implementing threading.
Normal applications should use
.Xr pthread_cond_timedwait 3
together with
.Xr pthread_cond_broadcast 3
for typical safe suspension with cooperation of the thread
being suspended, or
.Xr pthread_suspend_np 3
and
.Xr pthread_resume_np 3
in some specific situations, instead.
.Ef
.Pp
Passing the thread identifier of the calling thread
.Po
see
.Xr thr_self 2
.Pc
to
.Fn thr_wake
sets a thread's flag to cause the next signal-interruptible sleep
of that thread in the kernel to fail immediately with the
.Er EINTR
error.
The flag is cleared by an interruptible sleep attempt or by a call to
.Xr thr_suspend 2 .
This is used by the system threading library to implement cancellation.
.Pp
If
.Fa id
is not equal to the current thread identifier, the specified thread is
woken up if suspended by the
.Xr thr_suspend 2
system call.
If the thread is not suspended at the time of the
.Nm
call, the wake is remembered and the next attempt of the thread to
suspend itself with the
.Xr thr_suspend 2
results in immediate return with success.
Only one wake is remembered.
.Sh RETURN VALUES
.Rv -std thr_wake
.Sh ERRORS
The
.Fn thr_wake
operation returns these errors:
.Bl -tag -width Er
.It Bq Er ESRCH
The specified thread was not found or does not belong to the process
of the calling thread.
.El
.Sh SEE ALSO
.Xr ps 1 ,
.Xr thr_self 2 ,
.Xr thr_suspend 2 ,
.Xr pthread_cancel 3 ,
.Xr pthread_resume_np 3 ,
.Xr pthread_suspend_np 3
.Sh STANDARDS
The
.Fn thr_suspend
system call is non-standard and is used by
.Lb libthr
to implement
.St -p1003.1-2001
.Xr pthread 3
functionality.
.Sh HISTORY
The
.Fn thr_suspend
system call first appeared in
.Fx 5.2 .