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/*---------------------------------------------------------------------------*\ |
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$Id: poll.c,v 1.4 2003/01/01 19:02:29 bmc Exp $ |
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|
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NAME |
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|
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poll - select(2)-based poll() emulation function for BSD systems. |
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|
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SYNOPSIS |
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#include "poll.h" |
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|
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struct pollfd |
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{ |
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int fd; |
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short events; |
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short revents; |
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} |
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|
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int poll (struct pollfd *pArray, unsigned long n_fds, int timeout) |
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|
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DESCRIPTION |
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|
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This file, and the accompanying "poll.h", implement the System V |
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poll(2) system call for BSD systems (which typically do not provide |
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poll()). Poll() provides a method for multiplexing input and output |
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on multiple open file descriptors; in traditional BSD systems, that |
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capability is provided by select(). While the semantics of select() |
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differ from those of poll(), poll() can be readily emulated in terms |
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of select() -- which is how this function is implemented. |
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|
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REFERENCES |
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Stevens, W. Richard. Unix Network Programming. Prentice-Hall, 1990. |
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|
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NOTES |
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1. This software requires an ANSI C compiler. |
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|
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LICENSE |
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|
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This software is released under the following license: |
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|
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Copyright (c) 1995-2002 Brian M. Clapper |
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All rights reserved. |
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|
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Redistribution and use in source and binary forms are |
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permitted provided that: (1) source distributions retain |
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this entire copyright notice and comment; (2) modifications |
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made to the software are prominently mentioned, and a copy |
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of the original software (or a pointer to its location) are |
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included; and (3) distributions including binaries display |
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the following acknowledgement: "This product includes |
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software developed by Brian M. Clapper <bmc@clapper.org>" |
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in the documentation or other materials provided with the |
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distribution. The name of the author may not be used to |
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endorse or promote products derived from this software |
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without specific prior written permission. |
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|
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THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS |
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OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE |
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IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A |
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PARTICULAR PURPOSE. |
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|
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Effectively, this means you can do what you want with the software |
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except remove this notice or take advantage of the author's name. |
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If you modify the software and redistribute your modified version, |
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you must indicate that your version is a modification of the |
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original, and you must provide either a pointer to or a copy of the |
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original. |
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\*---------------------------------------------------------------------------*/ |
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|
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|
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/*---------------------------------------------------------------------------*\ |
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Includes |
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\*---------------------------------------------------------------------------*/ |
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|
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#if defined(HAVE_SYS_POLL_H) && defined(HAVE_POLL) |
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|
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#include <unistd.h> /* standard Unix definitions */ |
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#include <sys/types.h> /* system types */ |
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#include <sys/time.h> /* time definitions */ |
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#include <assert.h> /* assertion macros */ |
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#include <string.h> /* string functions */ |
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#include "poll.h" /* this package */ |
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|
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/*---------------------------------------------------------------------------*\ |
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Macros |
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\*---------------------------------------------------------------------------*/ |
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|
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#ifndef MAX |
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#define MAX(a,b) ((a) > (b) ? (a) : (b)) |
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#endif |
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|
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|
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/*---------------------------------------------------------------------------*\ |
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Private Functions |
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\*---------------------------------------------------------------------------*/ |
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|
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static int map_poll_spec |
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#if __STDC__ > 0 |
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(struct pollfd *pArray, |
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unsigned long n_fds, |
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fd_set *pReadSet, |
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fd_set *pWriteSet, |
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fd_set *pExceptSet) |
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#else |
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(pArray, n_fds, pReadSet, pWriteSet, pExceptSet) |
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struct pollfd *pArray; |
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unsigned long n_fds; |
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fd_set *pReadSet; |
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fd_set *pWriteSet; |
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fd_set *pExceptSet; |
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#endif |
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{ |
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register unsigned long i; /* loop control */ |
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register struct pollfd *pCur; /* current array element */ |
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register int max_fd = -1; /* return value */ |
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|
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/* |
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Map the poll() structures into the file descriptor sets required |
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by select(). |
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*/ |
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for (i = 0, pCur = pArray; i < n_fds; i++, pCur++) |
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{ |
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/* Skip any bad FDs in the array. */ |
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|
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if (pCur->fd < 0) |
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continue; |
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|
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if (pCur->events & POLLIN) |
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{ |
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/* "Input Ready" notification desired. */ |
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FD_SET (pCur->fd, pReadSet); |
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} |
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|
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if (pCur->events & POLLOUT) |
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{ |
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/* "Output Possible" notification desired. */ |
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FD_SET (pCur->fd, pWriteSet); |
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} |
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|
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if (pCur->events & POLLPRI) |
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{ |
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/* |
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"Exception Occurred" notification desired. (Exceptions |
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include out of band data. |
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*/ |
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FD_SET (pCur->fd, pExceptSet); |
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} |
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|
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max_fd = MAX (max_fd, pCur->fd); |
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} |
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|
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return max_fd; |
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} |
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|
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static struct timeval *map_timeout |
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#if __STDC__ > 0 |
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(int poll_timeout, struct timeval *pSelTimeout) |
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#else |
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(poll_timeout, pSelTimeout) |
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int poll_timeout; |
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struct timeval *pSelTimeout; |
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#endif |
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{ |
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struct timeval *pResult; |
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|
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/* |
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Map the poll() timeout value into a select() timeout. The possible |
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values of the poll() timeout value, and their meanings, are: |
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VALUE MEANING |
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-1 wait indefinitely (until signal occurs) |
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0 return immediately, don't block |
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>0 wait specified number of milliseconds |
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|
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select() uses a "struct timeval", which specifies the timeout in |
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seconds and microseconds, so the milliseconds value has to be mapped |
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accordingly. |
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*/ |
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|
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assert (pSelTimeout != (struct timeval *) NULL); |
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|
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switch (poll_timeout) |
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{ |
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case -1: |
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/* |
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A NULL timeout structure tells select() to wait indefinitely. |
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*/ |
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pResult = (struct timeval *) NULL; |
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break; |
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|
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case 0: |
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/* |
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"Return immediately" (test) is specified by all zeros in |
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a timeval structure. |
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*/ |
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pSelTimeout->tv_sec = 0; |
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pSelTimeout->tv_usec = 0; |
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pResult = pSelTimeout; |
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break; |
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|
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default: |
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/* Wait the specified number of milliseconds. */ |
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pSelTimeout->tv_sec = poll_timeout / 1000; /* get seconds */ |
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poll_timeout %= 1000; /* remove seconds */ |
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pSelTimeout->tv_usec = poll_timeout * 1000; /* get microseconds */ |
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pResult = pSelTimeout; |
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break; |
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} |
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|
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|
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return pResult; |
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} |
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|
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static void map_select_results |
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#if __STDC__ > 0 |
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(struct pollfd *pArray, |
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unsigned long n_fds, |
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fd_set *pReadSet, |
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fd_set *pWriteSet, |
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fd_set *pExceptSet) |
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#else |
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(pArray, n_fds, pReadSet, pWriteSet, pExceptSet) |
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struct pollfd *pArray; |
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unsigned long n_fds; |
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fd_set *pReadSet; |
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fd_set *pWriteSet; |
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fd_set *pExceptSet; |
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#endif |
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{ |
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register unsigned long i; /* loop control */ |
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register struct pollfd *pCur; /* current array element */ |
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|
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for (i = 0, pCur = pArray; i < n_fds; i++, pCur++) |
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{ |
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/* Skip any bad FDs in the array. */ |
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|
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if (pCur->fd < 0) |
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continue; |
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|
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/* Exception events take priority over input events. */ |
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|
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pCur->revents = 0; |
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if (FD_ISSET (pCur->fd, pExceptSet)) |
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pCur->revents |= POLLPRI; |
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|
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else if (FD_ISSET (pCur->fd, pReadSet)) |
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pCur->revents |= POLLIN; |
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|
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if (FD_ISSET (pCur->fd, pWriteSet)) |
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pCur->revents |= POLLOUT; |
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} |
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|
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return; |
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} |
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|
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/*---------------------------------------------------------------------------*\ |
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Public Functions |
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\*---------------------------------------------------------------------------*/ |
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|
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int poll |
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|
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#if __STDC__ > 0 |
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(struct pollfd *pArray, unsigned long n_fds, int timeout) |
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#else |
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(pArray, n_fds, timeout) |
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struct pollfd *pArray; |
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unsigned long n_fds; |
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int timeout; |
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#endif |
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|
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{ |
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fd_set read_descs; /* input file descs */ |
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fd_set write_descs; /* output file descs */ |
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fd_set except_descs; /* exception descs */ |
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struct timeval stime; /* select() timeout value */ |
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int ready_descriptors; /* function result */ |
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int max_fd; /* maximum fd value */ |
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struct timeval *pTimeout; /* actually passed */ |
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|
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FD_ZERO (&read_descs); |
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FD_ZERO (&write_descs); |
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FD_ZERO (&except_descs); |
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|
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assert (pArray != (struct pollfd *) NULL); |
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|
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/* Map the poll() file descriptor list in the select() data structures. */ |
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|
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max_fd = map_poll_spec (pArray, n_fds, |
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&read_descs, &write_descs, &except_descs); |
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|
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/* Map the poll() timeout value in the select() timeout structure. */ |
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|
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pTimeout = map_timeout (timeout, &stime); |
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|
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/* Make the select() call. */ |
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|
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ready_descriptors = select (max_fd + 1, &read_descs, &write_descs, |
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&except_descs, pTimeout); |
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|
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if (ready_descriptors >= 0) |
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{ |
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map_select_results (pArray, n_fds, |
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&read_descs, &write_descs, &except_descs); |
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} |
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|
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return ready_descriptors; |
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} |
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|
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#endif |
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|
