__WAKE_UP_SYNC_KEY(9) Driver Basics __WAKE_UP_SYNC_KEY(9)NAME
__wake_up_sync_key - wake up threads blocked on a waitqueue.
SYNOPSIS
void __wake_up_sync_key(wait_queue_head_t * q, unsigned int mode, int nr_exclusive, void * key);
ARGUMENTS
q
the waitqueue
mode
which threads
nr_exclusive
how many wake-one or wake-many threads to wake up
key
opaque value to be passed to wakeup targets
DESCRIPTION
The sync wakeup differs that the waker knows that it will schedule away soon, so while the target thread will be woken up, it will not be
migrated to another CPU - ie. the two threads are 'synchronized' with each other. This can prevent needless bouncing between CPUs.
On UP it can prevent extra preemption.
It may be assumed that this function implies a write memory barrier before changing the task state if and only if any tasks are woken up.
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 __WAKE_UP_SYNC_KEY(9)
Check Out this Related Man Page
SELRECORD(9) BSD Kernel Developer's Manual SELRECORD(9)NAME
selrecord, selwakeup -- record and wakeup select requests
SYNOPSIS
#include <sys/param.h>
#include <sys/selinfo.h>
void
selrecord(struct thread *td, struct selinfo *sip);
void
selwakeup(struct selinfo *sip);
DESCRIPTION
selrecord() and selwakeup() are the two central functions used by select(2), poll(2) and the objects that are being selected on. They handle
the task of recording which threads are waiting on which objects and the waking of the proper threads when an event of interest occurs on an
object.
selrecord() records that the calling thread is interested in events related to a given object. If another thread is already waiting on the
object a collision will be flagged in sip which will be later dealt with by selwakeup().
selrecord() acquires and releases sellock.
selwakeup() is called by the underlying object handling code in order to notify any waiting threads that an event of interest has occurred.
If a collision has occurred, selwakeup() will increment nselcoll, and broadcast on the global cv in order to wake all waiting threads so that
they can handle it. If the thread waiting on the object is not currently sleeping or the wait channel is not selwait, selwakeup() will clear
the TDF_SELECT flag which should be noted by select(2) and poll(2) when they wake up.
The contents of *sip must be zeroed, such as by softc initialization, before any call to selrecord() or selwakeup(), otherwise a panic may
occur. selwakeup() acquires and releases sellock and may acquire and release sched_lock.
SEE ALSO poll(2), select(2)AUTHORS
This manual page was written by Chad David <davidc@FreeBSD.org> and Alfred Perlstein <alfred@FreeBSD.org>.
BSD June 13, 2007 BSD
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