msleep msleep_spin pause tsleep wakeup - wait for events
The parameter
Fa chan
is an arbitrary address that uniquely identifies the event on which
the thread is being put to sleep.
All threads sleeping on a single
Fa chan
are woken up later by
wakeup (,);
often called from inside an interrupt routine, to indicate that the
resource the thread was blocking on is available now.
The parameter Fa priority specifies a new priority for the thread as well as some optional flags. If the new priority is not 0, then the thread will be made runnable with the specified Fa priority when it resumes. If Fa priority includes the PCATCH flag, signals are checked before and after sleeping, otherwise signals are not checked. If PCATCH is set and a signal needs to be delivered, Er ERESTART is returned if the current system call should be restarted if possible, and Er EINTR is returned if the system call should be interrupted by the signal (return Er EINTR ) .
The parameter Fa wmesg is a string describing the sleep condition for tools like ps(1). Due to the limited space of those programs to display arbitrary strings, this message should not be longer than 6 characters.
The parameter Fa timo specifies a timeout for the sleep. If Fa timo is not 0, then the thread will sleep for at most Fa timo No / Va hz seconds. If the timeout expires, then the sleep function will return Er EWOULDBLOCK .
Several of the sleep functions including
msleep (,);
msleep_spin (,);
and the locking primitive sleep routines specify an additional lock
parameter.
The lock will be released before sleeping and reacquired
before the sleep routine returns.
If
Fa priority
includes the
PDROP
flag, then
the lock will not be reacquired before returning.
The lock is used to ensure that a condition can be checked atomically,
and that the current thread can be suspended without missing a
change to the condition, or an associated wakeup.
In addition, all of the sleep routines will fully drop the
Giant
mutex
(even if recursed)
while the thread is suspended and will reacquire the
Giant
mutex before the function returns.
To avoid lost wakeups,
either a lock should be used to protect against races,
or a timeout should be specified to place an upper bound on the delay due
to a lost wakeup.
As a result,
the
tsleep ();
function should only be invoked with a timeout of 0 when the
Giant
mutex is held.
The
msleep ();
function requires that
Fa mtx
reference a default, i.e. non-spin, mutex.
Its use is deprecated in favor of
mtx_sleep9
which provides identical behavior.
The
msleep_spin ();
function requires that
Fa mtx
reference a spin mutex.
The
msleep_spin ();
function does not accept a
Fa priority
parameter and thus does not support changing the current thread's priority,
the
PDROP
flag,
or catching signals via the
PCATCH
flag.
The
pause ();
function is a wrapper around
tsleep ();
that suspends execution of the current thread for the indicated timeout.
The thread can not be awakened early by signals or calls to
wakeup ();
or
wakeup_one (.);
The
wakeup_one ();
function makes the first thread in the queue that is sleeping on the
parameter
Fa chan
runnable.
This reduces the load when a large number of threads are sleeping on
the same address, but only one of them can actually do any useful work
when made runnable.
Due to the way it works, the
wakeup_one ();
function requires that only related threads sleep on a specific
Fa chan
address.
It is the programmer's responsibility to choose a unique
Fa chan
value.
The older
wakeup ();
function did not require this, though it was never good practice
for threads to share a
Fa chan
value.
When converting from
wakeup ();
to
wakeup_one (,);
pay particular attention to ensure that no other threads wait on the
same
Fa chan .
The
tsleep ();
function appeared in
BSD 4.4
and added the parameters
Fa wmesg
and
Fa timo .
The
sleep ();
function was removed in
Fx 2.2 .
The
wakeup_one ();
function appeared in
Fx 2.2 .
The
msleep ();
function appeared in
Fx 5.0 ,
and the
msleep_spin ();
function appeared in
Fx 6.2 .
The
pause ();
function appeared in
Fx 7.0 .
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