NAME | SYNOPSIS | API RESTRICTIONS | DESCRIPTION | RETURN VALUES | ERRORS | ATTRIBUTES | SEE ALSO
#include <sys/types.h> #include <poll.h>int poll(int struct pollfd *fds, unsigned int nfds, int timeout[2]);
The function or functions documented here may not be used safely in all application contexts with all APIs provided in the ChorusOS 5.0 product.
See API(5FEA) for details.
The poll() function examines a set of file descriptors to see if some of them are ready for I/O. The fds argument is a pointer to an array of pollfd structures as defined in <poll.h> (shown below). The nfds argument determines the size of the fds array.
struct pollfd { int fd; /* file descriptor */ short events; /* events to look for */ short revents; /* events returned */ };
The fields of struct pollfd are as follows:
File descriptor to poll. If fd is equal to -1, revents is cleared (set to zero), and pollfd is not checked.
Events to poll for (see below).
Events which may occur (see below).
The event bitmasks in events and revents have the following bits:
Data other than high priority data may be read without blocking.
Normal data may be read without blocking.
Data with a non-zero priority may be read without blocking.
High priority data may be read without blocking.
Normal data may be written without blocking.
Data with a non-zero priority may be written without blocking.
An exceptional condition has occurred on the device or socket. This flag is always checked, even if not present in the events bitmask.
The device or socket has been disconnected. This flag is always checked, even if not present in the events bitmask. Note that POLLHUP and POLLOUT should never be present in the revents bitmask at the same time.
The file descriptor is not open. This flag is always checked, even if not present in the events bitmask.
If timeout is neither zero nor INFTIM (-1), it specifies a maximum interval to wait for any file descriptor to become ready, in milliseconds. If timeout is INFTIM (-1), the poll blocks indefinitely. If timeout is zero, poll() will return without blocking.
poll() returns the number of descriptors that are ready for I/O, or -1 if an error occured. If the time limit expires, poll() returns 0. If poll() returns with an error, including one due to an interrupted call, the fds array will be unmodified.
fds points outside the process's allocated address space.
A signal was delivered before the time limit expired and before any of the selected events occurred.
The specified time limit is negative.
See attributes(5) for descriptions of the following attributes:
ATTRIBUTE TYPE | ATTRIBUTE VALUE |
---|---|
Interface Stability | Evolving |
MT-level |
MT-safe |
accept(2POSIX), connect(2POSIX), read(2POSIX), recv(2POSIX), send(2POSIX), select(2POSIX), write(2POSIX)
NAME | SYNOPSIS | API RESTRICTIONS | DESCRIPTION | RETURN VALUES | ERRORS | ATTRIBUTES | SEE ALSO