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<!-- Copyright (C) 2003 Red Hat, Inc. --><!-- This material may be distributed only subject to the terms --><!-- and conditions set forth in the Open Publication License, v1.0 --><!-- or later (the latest version is presently available at --><!-- http://www.opencontent.org/openpub/). --><!-- Distribution of the work or derivative of the work in any --><!-- standard (paper) book form is prohibited unless prior --><!-- permission is obtained from the copyright holder. --><HTML><HEAD><TITLE>poll</TITLE><meta name="MSSmartTagsPreventParsing" content="TRUE"><METANAME="GENERATOR"CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+"><LINKREL="HOME"TITLE="eCos Reference Manual"HREF="ecos-ref.html"><LINKREL="UP"TITLE="TCP/IP Library Reference"HREF="tcpip-library-reference.html"><LINKREL="PREVIOUS"TITLE="ioctl"HREF="net-common-tcpip-manpages-ioctl.html"><LINKREL="NEXT"TITLE="select"HREF="net-common-tcpip-manpages-select.html"></HEAD><BODYCLASS="SECT1"BGCOLOR="#FFFFFF"TEXT="#000000"LINK="#0000FF"VLINK="#840084"ALINK="#0000FF"><DIVCLASS="NAVHEADER"><TABLESUMMARY="Header navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><THCOLSPAN="3"ALIGN="center">eCos Reference Manual</TH></TR><TR><TDWIDTH="10%"ALIGN="left"VALIGN="bottom"><AHREF="net-common-tcpip-manpages-ioctl.html"ACCESSKEY="P">Prev</A></TD><TDWIDTH="80%"ALIGN="center"VALIGN="bottom">Chapter 38. TCP/IP Library Reference</TD><TDWIDTH="10%"ALIGN="right"VALIGN="bottom"><AHREF="net-common-tcpip-manpages-select.html"ACCESSKEY="N">Next</A></TD></TR></TABLE><HRALIGN="LEFT"WIDTH="100%"></DIV><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="NET-COMMON-TCPIP-MANPAGES-POLL">poll</H1><TABLEBORDER="5"BGCOLOR="#E0E0F0"WIDTH="70%"><TR><TD><PRECLASS="SCREEN">POLL(2) System Calls Manual POLL(2)NAME poll - synchronous I/O multiplexingSYNOPSIS #include <poll.h> int poll(struct pollfd *fds, int nfds, int timeout);DESCRIPTION poll() provides a mechanism for reporting I/O conditions across a set of file descriptors. The arguments are as follows: fds Points to an array of pollfd structures, which are defined as: struct pollfd { int fd; short events; short revents; }; The fd member is an open file descriptor. The events and revents members are bitmasks of conditions to monitor and condi- tions found, respectively. nfds The number of pollfd structures in the array. timeout Maximum interval to wait for the poll to complete, in millisec- onds. If this value is 0, then poll() will return immediately. If this value is INFTIM (-1), poll() will block indefinitely until a condition is found. The calling process sets the events bitmask and poll() sets the revents bitmask. Each call to poll() resets the revents bitmask for accuracy. The condition flags in the bitmasks are defined as: POLLIN Data is available on the file descriptor for reading. POLLNORM Same as POLLIN. POLLPRI Same as POLLIN. POLLOUT Data can be written to the file descriptor without blocking. POLLERR This flag is not used in this implementation and is provided only for source code compatibility. POLLHUP The file descriptor was valid before the polling process and invalid after. Presumably, this means that the file descrip- tor was closed sometime during the poll. POLLNVAL The corresponding file descriptor is invalid. POLLRDNORM Same as POLLIN. POLLRDBAND Same as POLLIN. POLLWRNORM Same as POLLOUT. POLLWRBAND Same as POLLOUT. POLLMSG This flag is not used in this implementation and is provided only for source code compatibility. All flags except POLLIN, POLLOUT, and their synonyms are for use only in the revents member of the pollfd structure. An attempt to set any of these flags in the events member will generate an error condition. In addition to I/O multiplexing, poll() can be used to generate simple timeouts. This functionality may be achieved by passing a null pointer for fds.WARNINGS The POLLHUP flag is only a close approximation and may not always be accurate.RETURN VALUES Upon error, poll() returns a -1 and sets the global variable errno to indicate the error. If the timeout interval was reached before any events occurred, a 0 is returned. Otherwise, poll() returns the number of file descriptors for which revents is non-zero.ERRORS poll() will fail if: [EINVAL] nfds was either a negative number or greater than the number of available file descriptors. [EINVAL] An invalid flags was set in the events member of the pollfd structure. [EINVAL] The timeout passed to poll() was too large. [EAGAIN] Resource allocation failed inside of poll(). Subsequent calls to poll() may succeed. [EINTR] poll() caught a signal during the polling process.SEE ALSO poll(2), select(2), sysconf(3)HISTORY A poll() system call appeared in AT&T System V UNIX.BSD December 13, 1994 BSD </PRE></TD></TR></TABLE></DIV><DIVCLASS="NAVFOOTER"><HRALIGN="LEFT"WIDTH="100%"><TABLESUMMARY="Footer navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top"><AHREF="net-common-tcpip-manpages-ioctl.html"ACCESSKEY="P">Prev</A></TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="ecos-ref.html"ACCESSKEY="H">Home</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top"><AHREF="net-common-tcpip-manpages-select.html"ACCESSKEY="N">Next</A></TD></TR><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top">ioctl</TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="tcpip-library-reference.html"ACCESSKEY="U">Up</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top">select</TD></TR></TABLE></DIV></BODY></HTML>⌨️ 快捷键说明
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