1 '\" te
   2 .\"  Copyright (c) 2014, Joyent, Inc. All Rights Reserved.
   3 .\"  This file and its contents are supplied under the terms of the
   4 .\"  Common Development and Distribution License ("CDDL"), version 1.0.
   5 .\"  You may only use this file in accordance with the terms of version
   6 .\"  1.0 of the CDDL.
   7 .\"
   8 .\"  A full copy of the text of the CDDL should have accompanied this
   9 .\"  source.  A copy of the CDDL is also available via the Internet at
  10 .\"  http://www.illumos.org/license/CDDL.
  11 .TH EPOLL 5 "Apr 17, 2014"
  12 .SH NAME
  13 epoll \- Linux-compatible I/O event notification facility
  15 .nf
  16 #include <sys/epoll.h>
  17 .fi
  20 \fBepoll\fR is a facility for efficient event-oriented I/O that has a
  21 similar model to \fBpoll\fR(2), but does not necessitate rescanning a
  22 set of file descriptors to wait for an event.  \fBepoll\fR is of Linux
  23 origins, and this facility is designed to be binary-compatible with
  24 the Linux facility, including the following interfaces:
  26 .RS +4
  27 .TP
  28 .ie t \(bu
  29 .el o
  30 \fBepoll_create\fR(3C) creates an \fBepoll\fR instance, returning a file
  31 descriptor. It contains a size arugment which is meaningful only in as
  32 much as it cannot be 0.
  33 .RE
  34 .RS +4
  35 .TP
  36 .ie t \(bu
  37 .el o
  38 \fBepoll_create1\fR(3C) also creates an \fBepoll\fR instance, but eliminates
  39 the meaningless size argument -- replacing it instead with a flags
  40 argument.
  41 .RE
  42 .RS +4
  43 .TP
  44 .ie t \(bu
  45 .el o
  46 \fBepoll_ctl\fR(3C) allows file descriptors to be added
  47 (via \fBEPOLL_CTL_ADD\fR), deleted (via \fBEPOLL_CTL_DEL\fR) or
  48 modified (via \fBEPOLL_CTL_MOD\fR) with respect to the \fBepoll\fR'd set
  49 of file descriptors.
  50 .RE
  51 .RS +4
  52 .TP
  53 .ie t \(bu
  54 .el o
  55 \fBepoll_wait\fR(3C) fetches pending events for file descriptors added
  56 via \fBepoll_ctl\fR(3C), blocking the caller if no such events are pending.
  57 .RE
  58 .RS +4
  59 .TP
  60 .ie t \(bu
  61 .el o
  62 \fBepoll_pwait\fR(3C) opeates in a similar manner to \fBepoll_wait\fR(3C), but
  63 allows the caller to specify a signal mask to be set atomically with respect
  64 to waiting for events.
  65 .RE
  67 .sp
  68 .SH NOTES
  69 The \fBepoll\fR facility is implemented
  70 for purposes of offering compatibility to and portability of Linux-borne
  71 applications; native applications should continue to prefer using event ports
  72 via the \fBport_create\fR(3C),
  73 \fBport_associate\fR(3C) and \fBport_getn\fR(3C) interfaces.
  74 In particular, use of \fBepoll\fR in a multithreaded environment is fraught
  75 with peril; even when using \fBEPOLLONESHOT\fR for one-shot events,
  76 there are race conditions with respect to \fBclose\fR(2) that are unresolvable.
  77 (For more details, see the aborted effort in Linux to resolve this via the
  78 proposed
  79 \fBEPOLL_CTL_DISABLE\fR operation.)
  80 The event port facility -- like the BSD kqueue facility that inspired it --
  81 is designed to deal with such issues via explicit event source dissociation.
  83 While a best effort has been made to mimic the Linux semantics, there
  84 are some semantics that are too peculiar or ill-conceived to merit
  85 accommodation.  In particular, the Linux \fBepoll\fR facility will -- by
  86 design -- continue to generate events for closed file descriptors where/when
  87 the underlying file description remains open.  For example, if one were
  88 to \fBfork\fR(2) and subsequently close an actively \fBepoll\fR'd file
  89 descriptor in the parent,
  90 any events generated in the child on the implicitly duplicated file descriptor
  91 will continue to be delivered to the parent -- despite the fact that the
  92 parent itself no longer has any notion of the file description!
  93 This \fBepoll\fR facility refuses to honor
  94 these semantics; closing the \fBEPOLL_CTL_ADD\fR'd file descriptor
  95 will always result in no further
  96 events being generated for that event description.
  99 \fBepoll_create\fR(3C), \fBepoll_create1\fR(3C), \fBepoll_ctl\fR(3C),
 100 \fBepoll_wait\fR(3C), \fBepoll_pwait\fR(3C),
 101 \fBport_create\fR(3C), \fBport_associate\fR(3C), \fBport_dissociate\fR(3C),
 102 \fBport_get\fR(3C),
 103 \fBpselect\fR(3C)