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author | rgrimes <rgrimes@FreeBSD.org> | 1994-05-27 05:00:24 +0000 |
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committer | rgrimes <rgrimes@FreeBSD.org> | 1994-05-27 05:00:24 +0000 |
commit | be22b15ae2ff8d7fe06b6e14fddf0c5b444a95da (patch) | |
tree | a18a706dffa5baf86a3b12bbfb4f81caa097f349 /lib/libc/sys/select.2 | |
parent | 2a27bd86e6002c871e3b5561a5334653bb222a77 (diff) | |
download | FreeBSD-src-be22b15ae2ff8d7fe06b6e14fddf0c5b444a95da.zip FreeBSD-src-be22b15ae2ff8d7fe06b6e14fddf0c5b444a95da.tar.gz |
BSD 4.4 Lite Lib Sources
Diffstat (limited to 'lib/libc/sys/select.2')
-rw-r--r-- | lib/libc/sys/select.2 | 183 |
1 files changed, 183 insertions, 0 deletions
diff --git a/lib/libc/sys/select.2 b/lib/libc/sys/select.2 new file mode 100644 index 0000000..3de5b5e --- /dev/null +++ b/lib/libc/sys/select.2 @@ -0,0 +1,183 @@ +.\" Copyright (c) 1983, 1991, 1993 +.\" The Regents of the University of California. All rights reserved. +.\" +.\" 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. +.\" +.\" 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 8.2 (Berkeley) 3/25/94 +.\" +.Dd March 25, 1994 +.Dt SELECT 2 +.Os BSD 4.2 +.Sh NAME +.Nm select +.Nd synchronous I/O multiplexing +.Sh SYNOPSIS +.Fd #include <sys/types.h> +.Fd #include <sys/time.h> +.Fd #include <unistd.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 +.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 +.Fa nfds +descriptors are checked in each set; +i.e., the descriptors from 0 through +.Fa nfds Ns No -1 +in the descriptor sets are examined. +On return, +.Fn select +replaces the given descriptor sets +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 +.Fa fdset +to the null set. +.Fn FD_SET fd &fdset +includes a particular descriptor +.Fa fd +in +.Fa fdset . +.Fn FD_CLR fd &fdset +removes +.Fa fd +from +.Fa fdset . +.Fn FD_ISSET fd &fdset +is non-zero if +.Fa fd +is a member of +.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 +.Dv FD_SETSIZE , +which is normally at least equal +to the maximum number of descriptors supported by the system. +.Pp +If +.Fa timeout +is a non-nil pointer, it specifies a maximum interval to wait for the +selection to complete. If +.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 +.Fa readfds , +.Fa writefds , +and +.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, +or -1 if an error occurred. +If the time limit expires, +.Fn select +returns 0. +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. +.It Bq Er EINTR +A signal was delivered before the time limit expired and +before any of the selected events occurred. +.It Bq Er EINVAL +The specified time limit is invalid. One of its components is +negative or too large. +.El +.Sh SEE ALSO +.Xr accept 2 , +.Xr connect 2 , +.Xr getdtablesize 2 , +.Xr gettimeofday 2 , +.Xr read 2 , +.Xr recv 2 , +.Xr send 2 , +.Xr write 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 . |