SELRECORD(9) MidnightBSD 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〉.

MidnightBSD 0.3 June 13, 2007 MidnightBSD 0.3