selrecord(9) [freebsd man page]

SELRECORD(9)						   BSD Kernel Developer's Manual					      SELRECORD(9)

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>.

BSD
								  August 25, 2011							       BSD

Check Out this Related Man Page

SELECT(9)						   BSD Kernel Developer's Manual						 SELECT(9)

NAME

     seldestroy, selinit, selrecord, selnotify -- select and poll subsystem

SYNOPSIS

     #include <sys/param.h>
     #include <sys/select.h>

     void
     seldestroy(struct selinfo *sip);

     void
     selinit(struct selinfo *sip);

     void
     selrecord(struct lwp *selector, struct selinfo *sip);

     void
     selnotify(struct selinfo *sip, int events, long knhint);

DESCRIPTION

     selinit() and seldestroy() functions must be used to initialize and destroy the struct selinfo.  The seldestroy() function may block.

     selrecord() and selnotify() are used by device drivers to coordinate with the kernel implementation of select(2) and poll(2).  Each object
     that can be polled contains a selinfo record.  Device drivers provide locking for the selinfo record.

     selrecord() records that the calling thread is interested in events related to a given object.  selrecord() should only be called when the
     poll routine determines that the object is not ready for I/O: there are no events of interest pending.  The check for pending I/O and call to
     selrecord() must be atomic.  Atomicity can be provided by holding the object's lock across the test and call to selrecord().  For non-MPSAFE
     drivers, the global kernel_lock is enough to provide atomicity.

     selnotify() is called by the underlying object handling code in order to notify any waiting threads that an event of interest has occurred.
     The same lock held across the poll method and call to selrecord() must be held across the call to selnotify().  The lock prevents an event of
     interest being signalled while a thread is in the process of recording its interest.

     The events indicates which event happen.  Zero may be used if unknown.

     selnotify() also calls KNOTE() passing knhint as an argument.

CODE REFERENCES

     The core of the select and poll subsystem implementation is in sys/kern/sys_select.c.  Data structures and function prototypes are located in
     sys/sys/select.h, sys/sys/poll.h and sys/sys/selinfo.h.

SEE ALSO

     poll(2), select(2), knote(9)

BSD
								   May 13, 2008 							       BSD

Linux and UNIX Man Pages

selrecord(9) [freebsd man page]

Check Out this Related Man Page