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146 lines
4.9 KiB
Plaintext
146 lines
4.9 KiB
Plaintext
zmq_poll(3)
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===========
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NAME
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----
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zmq_poll - input/output multiplexing
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SYNOPSIS
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--------
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*int zmq_poll (zmq_pollitem_t '*items', int 'nitems', long 'timeout');*
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DESCRIPTION
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-----------
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The _zmq_poll()_ function provides a mechanism for applications to multiplex
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input/output events in a level-triggered fashion over a set of sockets. Each
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member of the array pointed to by the 'items' argument is a *zmq_pollitem_t*
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structure. The 'nitems' argument specifies the number of items in the 'items'
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array. The *zmq_pollitem_t* structure is defined as follows:
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["literal", subs="quotes"]
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typedef struct
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{
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void '*socket';
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zmq_fd_t 'fd';
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short 'events';
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short 'revents';
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} zmq_pollitem_t;
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For each *zmq_pollitem_t* item, _zmq_poll()_ shall examine either the 0MQ
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socket referenced by 'socket' *or* the standard socket specified by the file
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descriptor 'fd', for the event(s) specified in 'events'. If both 'socket' and
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'fd' are set in a single *zmq_pollitem_t*, the 0MQ socket referenced by
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'socket' shall take precedence and the value of 'fd' shall be ignored.
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For each *zmq_pollitem_t* item, _zmq_poll()_ shall first clear the 'revents'
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member, and then indicate any requested events that have occurred by setting the
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bit corresponding to the event condition in the 'revents' member.
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If none of the requested events have occurred on any *zmq_pollitem_t* item,
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_zmq_poll()_ shall wait 'timeout' milliseconds for an event to occur on
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any of the requested items. If the value of 'timeout' is `0`, _zmq_poll()_
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shall return immediately. If the value of 'timeout' is `-1`, _zmq_poll()_ shall
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block indefinitely until a requested event has occurred on at least one
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*zmq_pollitem_t*.
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The 'events' and 'revents' members of *zmq_pollitem_t* are bit masks constructed
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by OR'ing a combination of the following event flags:
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*ZMQ_POLLIN*::
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For 0MQ sockets, at least one message may be received from the 'socket' without
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blocking. For standard sockets this is equivalent to the 'POLLIN' flag of the
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_poll()_ system call and generally means that at least one byte of data may be
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read from 'fd' without blocking.
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*ZMQ_POLLOUT*::
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For 0MQ sockets, at least one message may be sent to the 'socket' without
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blocking. For standard sockets this is equivalent to the 'POLLOUT' flag of the
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_poll()_ system call and generally means that at least one byte of data may be
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written to 'fd' without blocking.
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*ZMQ_POLLERR*::
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For standard sockets, this flag is passed through _zmq_poll()_ to the
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underlying _poll()_ system call and generally means that some sort of error
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condition is present on the socket specified by 'fd'. For 0MQ sockets this flag
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has no effect if set in 'events', and shall never be returned in 'revents' by
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_zmq_poll()_.
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*ZMQ_POLLPRI*::
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For 0MQ sockets this flags is of no use. For standard sockets this means there
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is urgent data to read. Refer to the POLLPRI flag for more information.
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For file descriptor, refer to your use case: as an example, GPIO interrupts
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are signaled through a POLLPRI event.
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This flag has no effect on Windows.
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NOTE: The _zmq_poll()_ function may be implemented or emulated using operating
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system interfaces other than _poll()_, and as such may be subject to the limits
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of those interfaces in ways not defined in this documentation.
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THREAD SAFETY
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-------------
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The *zmq_pollitem_t* array must only be used by the thread which
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will/is calling _zmq_poll_.
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If a socket is contained in multiple *zmq_pollitem_t* arrays, each owned by a
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different thread, the socket itself needs to be thread-safe (Server, Client, ...).
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Otherwise, behaviour is undefined.
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RETURN VALUE
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------------
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Upon successful completion, the _zmq_poll()_ function shall return the number
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of *zmq_pollitem_t* structures with events signaled in 'revents' or `0` if no
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events have been signaled. Upon failure, _zmq_poll()_ shall return `-1` and set
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'errno' to one of the values defined below.
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ERRORS
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------
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*ETERM*::
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At least one of the members of the 'items' array refers to a 'socket' whose
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associated 0MQ 'context' was terminated.
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*EFAULT*::
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The provided 'items' was not valid (NULL).
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*EINTR*::
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The operation was interrupted by delivery of a signal before any events were
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available.
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EXAMPLE
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-------
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.Polling indefinitely for input events on both a 0MQ socket and a standard socket.
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----
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zmq_pollitem_t items [2];
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/* First item refers to 0MQ socket 'socket' */
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items[0].socket = socket;
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items[0].events = ZMQ_POLLIN;
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/* Second item refers to standard socket 'fd' */
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items[1].socket = NULL;
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items[1].fd = fd;
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items[1].events = ZMQ_POLLIN;
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/* Poll for events indefinitely */
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int rc = zmq_poll (items, 2, -1);
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assert (rc >= 0);
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/* Returned events will be stored in items[].revents */
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----
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SEE ALSO
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--------
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linkzmq:zmq_socket[3]
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linkzmq:zmq_send[3]
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linkzmq:zmq_recv[3]
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linkzmq:zmq[7]
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Your operating system documentation for the _poll()_ system call.
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AUTHORS
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-------
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This page was written by the 0MQ community. To make a change please
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read the 0MQ Contribution Policy at <http://www.zeromq.org/docs:contributing>.
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