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);
DESCRIPTIONselrecord() and selwakeup() are the two central functions used by
select(2), poll(2) and the objects that are being selected on. They han‐
dle 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 broad‐
cast 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 ALSOpoll(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
