BSD 4_4 release

[unix-history] / usr / src / lib / libc / sys / select.2

diff --git a/usr/src/lib/libc/sys/select.2 b/usr/src/lib/libc/sys/select.2
index 82499cd..3c757cd 100644 (file)
--- a/usr/src/lib/libc/sys/select.2
+++ b/usr/src/lib/libc/sys/select.2
@@ -1,121 +1,182 @@
-.\" Copyright (c) 1983 Regents of the University of California.
-.\" All rights reserved.  The Berkeley software License Agreement
-.\" specifies the terms and conditions for redistribution.
+.\" Copyright (c) 1983, 1991, 1993
+.\"    The Regents of the University of California.  All rights reserved.

 .\"
 .\"

-.\"    @(#)select.2    6.3 (Berkeley) %G%
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"    This product includes software developed by the University of
+.\"    California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.

 .\"
 .\"

-.TH SELECT 2 ""
-.UC 5
-.SH NAME
-select \- synchronous i/o multiplexing
-.SH SYNOPSIS
-.nf
-.ft B
-#include <sys/types.h>
-#include <sys/time.h>
-.PP
-.ft B
-nfound = select(nfds, readfds, writefds, exceptfds, timeout)
-int nfound, nfds;
-fd_set *readfds, *writefds, *exceptfds;
-struct timeval *timeout;
-.PP
-.ft B
-int fd;
-fd_set fdset;
-FD_SET(fd, &fdset)     
-FD_CLR(fd, &fdset)     
-FD_ISSET(fd, &fdset)   
-FD_ZERO(&fdset)        
-.fi
-.SH DESCRIPTION
-.I Select
-examines the i/o descriptor sets whose addresses are passed in
-.IR readfds ,
-.IR writefds ,
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"     @(#)select.2   8.1 (Berkeley) 6/4/93
+.\"
+.Dd June 4, 1993
+.Dt SELECT 2
+.Os BSD 4.2
+.Sh NAME
+.Nm select
+.Nd synchronous I/O multiplexing
+.Sh SYNOPSIS
+.Fd #include <unistd.h>
+.Fd #include <sys/types.h>
+.Fd #include <sys/time.h>
+.Ft int
+.Fn select "int nfds" "fd_set *readfds" "fd_set *writefds" "fd_set *exceptfds" "struct timeval *timeout"
+.Fn FD_SET fd &fdset
+.Fn FD_CLR fd &fdset
+.Fn FD_ISSET fd &fdset
+.Fn FD_ZERO &fdset
+.Sh DESCRIPTION
+.Fn Select
+examines the I/O descriptor sets whose addresses are passed in
+.Fa readfds ,
+.Fa writefds ,

 and
 and

-.I exceptfds
+.Fa exceptfds

 to see if some of their descriptors
 are ready for reading, are ready for writing, or have an exceptional
 condition pending, respectively.
 The first
 to see if some of their descriptors
 are ready for reading, are ready for writing, or have an exceptional
 condition pending, respectively.
 The first

-.I nfds
+.Fa nfds

 descriptors are checked in each set;
 descriptors are checked in each set;

-i.e. the descriptors from 0 through
-.IR nfds -1
+i.e., the descriptors from 0 through
+.Fa nfds Ns No -1

 in the descriptor sets are examined.
 On return,
 in the descriptor sets are examined.
 On return,

-.I select
+.Fn select

 replaces the given descriptor sets
 replaces the given descriptor sets

-with subsets consisting of those descriptors that are ready.
-The total number of ready descriptors in all the sets is returned in
-.IR nfound .
-.PP
-Some macros are provided for manipulating descriptor sets.
-.I "FD_ZERO(&fdset)"
+with subsets consisting of those descriptors that are ready
+for the requested operation.
+.Fn Select
+returns the total number of ready descriptors in all the sets.
+.Pp
+The descriptor sets are stored as bit fields in arrays of integers.
+The following macros are provided for manipulating such descriptor sets:
+.Fn FD_ZERO &fdsetx

 initializes a descriptor set
 initializes a descriptor set

-.I fdset
+.Fa fdset

 to the null set.
 to the null set.

-.I "FD_SET(fd, &fdset)"
+.Fn FD_SET fd &fdset

 includes a particular descriptor
 includes a particular descriptor

-.I fd
+.Fa fd

 in
 in

-.IR fdset .
-.I "FD_CLR(fd, &fdset)"
+.Fa fdset .
+.Fn FD_CLR fd &fdset

 removes
 removes

-.I fd
+.Fa fd

 from
 from

-.IR fdset .
-.I "FD_ISSET(fd, &fdset)"
-is nonzero if
-.I fd
+.Fa fdset .
+.Fn FD_ISSET fd &fdset
+is non-zero if
+.Fa fd

 is a member of
 is a member of

-.IR fdset ,
+.Fa fdset ,

 zero otherwise.
 The behavior of these macros is undefined if
 a descriptor value is less than zero or greater than or equal to
 zero otherwise.
 The behavior of these macros is undefined if
 a descriptor value is less than zero or greater than or equal to

-.IR FD_SETSIZE ,
+.Dv FD_SETSIZE ,

 which is normally at least equal
 to the maximum number of descriptors supported by the system.
 which is normally at least equal
 to the maximum number of descriptors supported by the system.

-.PP
+.Pp

 If
 If

-.I timeout
-is a non-zero pointer, it specifies a maximum interval to wait for the
+.Fa timeout
+is a non-nil pointer, it specifies a maximum interval to wait for the

 selection to complete.  If 
 selection to complete.  If 

-.I timeout
-is a zero pointer, the select blocks indefinitely.  To affect a poll, the
-.I timeout
-argument should be non-zero, pointing to a zero valued timeval structure.
-.PP
+.Fa timeout
+is a nil pointer, the select blocks indefinitely.  To affect a poll, the
+.Fa timeout
+argument should be non-nil, pointing to a zero-valued timeval structure.
+.Pp

 Any of
 Any of

-.IR readfds ,
-.IR writefds ,
+.Fa readfds ,
+.Fa writefds ,

 and
 and

-.I exceptfds
-may be given as zero pointers if no descriptors are of interest.
-.SH "RETURN VALUE
-.I Select
+.Fa exceptfds
+may be given as nil pointers if no descriptors are of interest.
+.Sh RETURN VALUES
+.Fn Select

 returns the number of ready descriptors that are contained in
 the descriptor sets,
 returns the number of ready descriptors that are contained in
 the descriptor sets,

-or \-1 if an error occurred.
-If the time limit expires then
-.I select
+or -1 if an error occurred.
+If the time limit expires,
+.Fn select

 returns 0.
 returns 0.

-.SH "ERRORS
-An error return from \fIselect\fP indicates:
-.TP 15
-[EBADF]
+If
+.Fn select
+returns with an error,
+including one due to an interrupted call,
+the descriptor sets will be unmodified.
+.Sh ERRORS
+An error return from
+.Fn select
+indicates:
+.Bl -tag -width Er
+.It Bq Er EBADF

 One of the descriptor sets specified an invalid descriptor.
 One of the descriptor sets specified an invalid descriptor.

-.TP 15
-[EINTR]
+.It Bq Er EINTR

 A signal was delivered before the time limit expired and
 before any of the selected events occurred.
 A signal was delivered before the time limit expired and
 before any of the selected events occurred.

-.TP 15
-[EINVAL]
+.It Bq Er EINVAL

 The specified time limit is invalid.  One of its components is
 negative or too large.
 The specified time limit is invalid.  One of its components is
 negative or too large.

-.SH SEE ALSO
-accept(2), connect(2), read(2), write(2), recv(2), send(2), getdtablesize(2)
-.SH BUGS
-The descriptor sets are always modified on return, even
-if the call returns as the result of the timeout.
+.El
+.Sh SEE ALSO
+.Xr accept 2 ,
+.Xr connect 2 ,
+.Xr read 2 ,
+.Xr write 2 ,
+.Xr recv 2 ,
+.Xr send 2 ,
+.Xr getdtablesize 2
+.Sh BUGS
+Although the provision of
+.Xr getdtablesize 2
+was intended to allow user programs to be written independent
+of the kernel limit on the number of open files, the dimension
+of a sufficiently large bit field for select remains a problem.
+The default size
+.Dv FD_SETSIZE
+(currently 256) is somewhat larger than
+the current kernel limit to the number of open files.
+However, in order to accommodate programs which might potentially
+use a larger number of open files with select, it is possible
+to increase this size within a program by providing
+a larger definition of
+.Dv FD_SETSIZE
+before the inclusion of
+.Aq Pa sys/types.h .
+.Pp
+.Fn Select
+should probably return the time remaining from the original timeout,
+if any, by modifying the time value in place.
+This may be implemented in future versions of the system.
+Thus, it is unwise to assume that the timeout value will be unmodified
+by the
+.Fn select
+call.
+.Sh HISTORY
+The
+.Nm
+function call appeared in
+.Bx 4.2 .