NAME

       zmq_ppoll - input/output multiplexing with signal mask

SYNOPSIS

       int zmq_ppoll (zmq_pollitem_t *items, int nitems, long timeout, const sigset_t *sigmask);

DESCRIPTION

       The relationship between zmq_poll() and zmq_ppoll() is analogous to the relationship
       between poll(2) and ppoll(2) and between select(2) and pselect(2): zmq_ppoll() allows an
       application to safely wait until either a file descriptor becomes ready or until a signal
       is caught.

       When using zmq_ppoll() with sigmask set to NULL, its behavior is identical to that of
       zmq_poll(). See zmq_poll(3) for more on this.

       To make full use of zmq_ppoll(), a non-NULL pointer to a signal mask must be constructed
       and passed to sigmask. See sigprocmask(2) for more details. When this is done, inside the
       actual ppoll() (or pselect(), see note below) system call, an atomic operation consisting
       of three steps is performed: 1. The current signal mask is replaced by the one pointed to
       by sigmask. 2. The actual poll() call is done. 3. The original signal mask is restored.
       Because these operations are done atomically, there is no opportunity for race conditions
       in between the calls changing the signal mask and the poll/select system call. This means
       that only during this (atomic) call, we can unblock certain signals, so that they can be
       handled at that time only, not outside of the call. This means that effectively, we extend
       our poller into a function that not only watches sockets for changes, but also watches the
       "POSIX signal socket" for incoming signals. At other times, these signals will be blocked,
       and we will not have to deal with interruptions in system calls at these other times.

           Note
           The zmq_ppoll() function may be implemented or emulated using operating system
           interfaces other than ppoll(), and as such may be subject to the limits of those
           interfaces in ways not defined in this documentation.

           Note
           There is no ppoll or pselect on Windows, so zmq_ppoll() is not supported in Windows
           builds. It is still callable, but its sigmask has void pointer type (because sigset_t
           is also not available on Windows) and zmq_ppoll() will return with an error (see error
           section below).

THREAD SAFETY

       The zmq_pollitem_t array must only be used by the thread which will/is calling zmq_ppoll.

       If a socket is contained in multiple zmq_pollitem_t arrays, each owned by a different
       thread, the socket itself needs to be thead-safe (Server, Client, ...). Otherwise,
       behaviour is undefined.

RETURN VALUE

       Upon successful completion, the zmq_ppoll() function shall return the number of
       zmq_pollitem_t structures with events signaled in revents or 0 if no events have been
       signaled. Upon failure, zmq_ppoll() shall return -1 and set errno to one of the values
       defined below.

ERRORS

       ETERM
           At least one of the members of the items array refers to a socket whose associated 0MQ
           context was terminated.

       EFAULT
           The provided items was not valid (NULL).

       EINTR
           The operation was interrupted by delivery of a signal before any events were
           available.

       EINTR
           The operation was interrupted by delivery of a signal before any events were
           available.

       ENOTSUP
           zmq_ppoll() was not activated in this build.

EXAMPLE

       Polling indefinitely for input events on both a 0MQ socket and a standard socket.. See the
       example section of zmq_poll(3). One only needs to replace the zmq_poll call with zmq_ppoll
       and add a NULL argument for the sigmask parameter.

       Handle SIGTERM during zmq_ppoll (and block it otherwise)..

           // simple global signal handler for SIGTERM
           static bool sigterm_received = false;
           void handle_sigterm (int signum) {
               sigterm_received = true;
           }

           // set up signal mask and install handler for SIGTERM
           sigset_t sigmask, sigmask_without_sigterm;
           sigemptyset(&sigmask);
           sigaddset(&sigmask, SIGTERM);
           sigprocmask(SIG_BLOCK, &sigmask, &sigmask_without_sigterm);
           struct sigaction sa;
           memset(&sa, '\0', sizeof(sa));
           sa.sa_handler = handle_sigterm;

           // poll
           zmq_pollitem_t items [1];
           // Just one item, which refers to 0MQ socket 'socket' */
           items[0].socket = socket;
           items[0].events = ZMQ_POLLIN;
           // Poll for events indefinitely, but also exit on SIGTERM
           int rc = zmq_poll (items, 2, -1, &sigmask_without_sigterm);
           if (rc < 0 && errno == EINTR && sigterm_received) {
             // do your SIGTERM business
           } else {
             // do your non-SIGTERM error handling
           }

SEE ALSO

       zmq_poll(3) zmq_socket(3) zmq_send(3) zmq_recv(3) zmq(7)

       Your operating system documentation for the poll() system call.

AUTHORS

       This page was written by the 0MQ community. To make a change please read the 0MQ
       Contribution Policy at http://www.zeromq.org/docs:contributing.