path: root/share/man/man9/timeout.9

.\"	$OpenBSD: timeout.9,v 1.55 2022/06/22 14:10:49 visa Exp $
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.Dd $Mdocdate: June 22 2022 $
.Dt TIMEOUT_SET 9
.Os
.Sh NAME
.Nm timeout_set ,
.Nm timeout_set_flags ,
.Nm timeout_set_proc ,
.Nm timeout_add ,
.Nm timeout_add_sec ,
.Nm timeout_add_msec ,
.Nm timeout_add_nsec ,
.Nm timeout_add_usec ,
.Nm timeout_add_tv ,
.Nm timeout_del ,
.Nm timeout_del_barrier ,
.Nm timeout_barrier ,
.Nm timeout_pending ,
.Nm timeout_initialized ,
.Nm timeout_triggered ,
.Nm TIMEOUT_INITIALIZER ,
.Nm TIMEOUT_INITIALIZER_FLAGS
.Nd execute a function after a specified period of time
.Sh SYNOPSIS
.In sys/types.h
.In sys/timeout.h
.Ft void
.Fn timeout_set "struct timeout *to" "void (*fn)(void *)" "void *arg"
.Ft void
.Fo timeout_set_flags
.Fa "struct timeout *to"
.Fa "void (*fn)(void *)"
.Fa "void *arg"
.Fa "int flags"
.Fc
.Ft void
.Fn timeout_set_proc "struct timeout *to" "void (*fn)(void *)" "void *arg"
.Ft int
.Fn timeout_add "struct timeout *to" "int ticks"
.Ft int
.Fn timeout_del "struct timeout *to"
.Ft int
.Fn timeout_del_barrier "struct timeout *to"
.Ft void
.Fn timeout_barrier "struct timeout *to"
.Ft int
.Fn timeout_pending "struct timeout *to"
.Ft int
.Fn timeout_initialized "struct timeout *to"
.Ft int
.Fn timeout_triggered "struct timeout *to"
.Ft int
.Fn timeout_add_tv "struct timeout *to" "struct timeval *"
.Ft int
.Fn timeout_add_sec "struct timeout *to" "int sec"
.Ft int
.Fn timeout_add_msec "struct timeout *to" "int msec"
.Ft int
.Fn timeout_add_usec "struct timeout *to" "int usec"
.Ft int
.Fn timeout_add_nsec "struct timeout *to" "int nsec"
.Fn TIMEOUT_INITIALIZER "void (*fn)(void *)" "void *arg"
.Fn TIMEOUT_INITIALIZER_FLAGS "void (*fn)(void *)" "void *arg" "int flags"
.Sh DESCRIPTION
The
.Nm timeout
API provides a mechanism to execute a function at a given time.
The granularity of the time is limited by the granularity of the
.Xr hardclock 9
timer which executes
.Xr hz 9
times a second.
.Pp
It is the responsibility of the caller to provide these functions with
pre-allocated timeout structures.
.Pp
The
.Fn timeout_set
function prepares the timeout structure
.Fa to
to be used in future calls to
.Fn timeout_add
and
.Fn timeout_del .
The timeout will be prepared to call the function specified by the
.Fa fn
argument with a
.Fa void *
argument given in the
.Fa arg
argument.
Once initialized, the
.Fa to
structure can be used repeatedly in
.Fn timeout_add
and
.Fn timeout_del
and does not need to be reinitialized unless
the function called and/or its argument must change.
.Pp
The
.Fn timeout_set_flags
function is similar to
.Fn timeout_set
but it additionally accepts the bitwise OR of zero or more of the
following
.Fa flags :
.Bl -tag -width TIMEOUT_PROC -offset indent
.It Dv TIMEOUT_PROC
Runs the timeout in a process context instead of the default
.Dv IPL_SOFTCLOCK
interrupt context.
.El
.Pp
The
.Fn timeout_set_proc
function is similar to
.Fn timeout_set
but it runs the timeout in a process context instead of the default
.Dv IPL_SOFTCLOCK
interrupt context.
.Pp
The function
.Fn timeout_add
schedules the execution of the
.Fa to
timeout in at least
.Fa ticks Ns /hz
seconds.
Negative values of
.Fa ticks
are illegal.
If the value is
.Sq 0
it will, in the current implementation, be treated as
.Sq 1 ,
but in the future it might cause an immediate timeout.
The timeout in the
.Fa to
argument must be already initialized by
.Fn timeout_set ,
.Fn timeout_set_flags ,
or
.Fn timeout_set_proc
and may not be used in calls to
.Fn timeout_set ,
.Fn timeout_set_flags ,
or
.Fn timeout_set_proc
until it has timed out or been removed with
.Fn timeout_del .
If the timeout in the
.Fa to
argument is already scheduled, the old execution time will be
replaced by the new one.
.Pp
The function
.Fn timeout_del
will cancel the timeout in the argument
.Fa to .
If the timeout has already executed or has never been added,
the call will have no effect.
.Pp
.Fn timeout_del_barrier
is like
.Fn timeout_del
but it will wait until any current execution of the timeout has completed.
.Pp
.Fn timeout_barrier
ensures that any current execution of the timeout in the argument
.Fa to
has completed before returning.
.Pp
The caller of
.Fn timeout_barrier
or
.Fn timeout_del_barrier
must not hold locks that can block processing in the timeout's context.
Otherwise, the system will deadlock.
.Pp
The
.Fn timeout_pending
macro can be used to check if a timeout is scheduled to run.
.Pp
The
.Fn timeout_initialized
macro can be used to check if a timeout has been initialized.
.Pp
The
.Fn timeout_triggered
macro can be used to check if a timeout is running or has been run.
The
.Fn timeout_add
and
.Fn timeout_del
functions clear the triggered state for that timeout.
.Pp
When possible, use the
.Fn timeout_add_tv ,
.Fn timeout_add_sec ,
.Fn timeout_add_msec ,
.Fn timeout_add_usec ,
and
.Fn timeout_add_nsec
functions instead of
.Fn timeout_add .
Those functions add a timeout whilst converting the time specified
by the respective types.
They also defer the timeout handler for at least one tick if called
with a positive value.
.Pp
A timeout declaration can be initialised with the
.Fn TIMEOUT_INITIALIZER
macro.
The timeout will be prepared to call the function specified by the
.Fa fn
argument with the
.Fa void *
argument given in
.Fa arg .
.Pp
The
.Fn TIMEOUT_INITIALIZER_FLAGS
macro is similar to
.Fn TIMEOUT_INITIALIZER ,
but it accepts additional flags.
See the
.Fn timeout_set_flags
function for details.
.Sh CONTEXT
.Fn timeout_set ,
.Fn timeout_set_flags ,
and
.Fn timeout_set_proc
can be called during autoconf, from process context, or from interrupt
context.
.Pp
.Fn timeout_add ,
.Fn timeout_add_sec ,
.Fn timeout_add_msec ,
.Fn timeout_add_nsec ,
.Fn timeout_add_usec ,
.Fn timeout_add_tv ,
.Fn timeout_del ,
.Fn timeout_pending ,
.Fn timeout_initialized ,
.Fn timeout_triggered
can be called during autoconf, from process context, or from any
interrupt context at or below
.Dv IPL_CLOCK .
.Pp
.Fn timeout_barrier
and
.Fn timeout_del_barrier
can be called from process context.
.Pp
When the timeout runs, the
.Fa fn
argument to
.Fn timeout_set
or
.Fn timeout_set_flags
will be called in an interrupt context at
.Dv IPL_SOFTCLOCK
or a process context if the
.Dv TIMEOUT_PROC
flag was given at initialization.
The
.Fa fn
argument to
.Fn timeout_set_proc
will be called in a process context.
.Sh RETURN VALUES
.Fn timeout_add ,
.Fn timeout_add_sec ,
.Fn timeout_add_msec ,
.Fn timeout_add_nsec ,
.Fn timeout_add_usec ,
and
.Fn timeout_add_tv
will return 1 if the timeout
.Fa to
was added to the timeout schedule or 0 if it was already queued.
.Pp
.Fn timeout_del
and
.Fn timeout_del_barrier
will return 1 if the timeout
.Fa to
was removed from the pending timeout schedule or 0 if it was not
currently queued.
.Sh CODE REFERENCES
These functions are implemented in the file
.Pa sys/kern/kern_timeout.c .
.Sh SEE ALSO
.Xr hz 9 ,
.Xr splclock 9 ,
.Xr tsleep 9 ,
.Xr tvtohz 9
.Rs
.%A George Varghese
.%A Anthony Lauck
.%B Hashed and hierarchical timing wheels: efficient data structures for \
implementing a timer facility
.%O especially Schemes 6 and 7
.%I IEEE/ACM
.%J Transactions on Networking
.%V vol. 5
.%N no. 6
.%P pp. 824\(en834
.%D December 1997
.Re