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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_SUSPEND 2
.Os
.Sh NAME
.Nm thr_suspend
.Nd suspend the calling thread
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/thr.h
.Ft int
.Fn thr_suspend "struct timespec *timeout"
.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
The
.Fn thr_suspend
system call puts the calling thread in a suspended state, where it is
not eligible for CPU time.
This state is exited by another thread calling
.Xr thr_wake 2 ,
when the time interval specified by
.Fa timeout
has elapsed,
or by the delivery of a signal to the suspended thread.
.Pp
If the
.Fa timeout
argument is
.Dv NULL ,
the suspended state can be only terminated by explicit
.Fn thr_wake
or signal.
.Pp
If a wake from
.Xr thr_wake 2
was delivered before the
.Nm
call, the thread is not put into a suspended state.
Instead, the call
returns immediately without an error.
.Pp
If a thread previously called
.Xr thr_wake 2
with its own thread identifier, which resulted in setting the internal kernel
flag to immediately abort interruptible sleeps with an
.Er EINTR
error
.Po
see
.Xr thr_wake 2
.Pc ,
the flag is cleared.
As with
.Xr thr_wake 2
called from another thread, the next
.Nm
call does not result in suspension.
.Pp
.Sh RETURN VALUES
.Rv -std thr_suspend
.Sh ERRORS
The
.Fn thr_suspend
operation returns the following errors:
.Bl -tag -width Er
.It Bq Er EFAULT
The memory pointed to by the
.Fa timeout
argument is not valid.
.It Bq Er ETIMEDOUT
The specified timeout expired.
.It Bq Er ETIMEDOUT
The
.Fa timeout
argument specified a zero time interval.
.It Bq Er EINTR
The sleep was interrupted by a signal.
.El
.Sh SEE ALSO
.Xr ps 1 ,
.Xr thr_wake 2 ,
.Xr pthread_resume_np 3 ,
.Xr pthread_suspend_np 3
.Sh STANDARDS
The
.Fn thr_suspend
system call is non-standard.
.Sh HISTORY
The
.Fn thr_suspend
system call first appeared in
.Fx 5.2 .