NAME¶
seldrain
,
selrecord
,
selwakeup
—
record and wakeup select requests
SYNOPSIS¶
#include
<sys/param.h>
#include
<sys/selinfo.h>
void
seldrain
(
struct
selinfo *sip);
void
selrecord
(
struct
thread *td,
struct selinfo
*sip);
void
selwakeup
(
struct
selinfo *sip);
DESCRIPTION¶
seldrain
(),
selrecord
() and
selwakeup
() are the three 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.
seldrain
() will flush the waiters queue on a
specified object before its destruction. The object handling code must ensure
that
*sip cannot be used once
seldrain
() has been called.
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.
seldrain
() could usually be just a wrapper
for
selwakeup
(), but consumers should not
generally rely on this feature.
SEE ALSO¶
poll(2),
select(2)
AUTHORS¶
This manual page was written by
Chad David
⟨davidc@FreeBSD.org⟩ and
Alfred
Perlstein ⟨alfred@FreeBSD.org⟩.