poll - wait for some event on a file descriptor
poll(2) is a variation on the theme of select. It specifies an array of nfds structures of type
and a timeout in milliseconds. A negative value means infinite timeout. The field fd contains a file descriptor for an open file. The field events is an input parameter, a bitmask specifying the events the application is interested in. The field revents is an output parameter, filled by the kernel with the events that actually occurred, either of the type requested, or of one of the types POLLERR or POLLHUP or POLLNVAL. (These three bits are meaningless in the events field, and will be set in the revents field whenever the corresponding condition is true.) If none of the events requested (and no error) has occurred for any of the file descriptors, the kernel waits for timeout milliseconds for one of these events to occur. The following possible bits in these masks are defined in '<sys/poll.h>'
In POLLRDNORM, POLLRDBAND, POLLWRNORM, POLLWRBAND and POLLMSG__ are defined.
On success, a positive number is returned, where the number returned is the number of structures which have non-zero revents fields (in other words, those descriptors with events or errors reported). A value of 0 indicates that the call timed out and no file descriptors have been selected. On error, -1 is returned, and errno is set appropriately.
The poll() systemcall was introduced in Linux 2.1.23. The poll() library call was introduced in libc 5.4.28 (and provides emulation using select if your kernel does not have a poll syscall).
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