The <poll.h> header shall define the sigset_t type as described in <signal.h>.
The <poll.h> header shall define the timespec structure as described in <time.h>.

The following shall be declared as a function and may also be defined as a macro. A function prototype shall be provided.
int poll(struct pollfd [], nfds_t, int);

The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.
int poll(struct pollfd [], nfds_t, int);
int ppoll(struct pollfd [], nfds_t, const struct timespec *restrict, const sigset_t *restrict);
Inclusion of the <poll.h> header may make visible all symbols from the headers
<signal.h> and <time.h>.

poll

poll, ppoll

int ppoll(struct pollfd fds[], nfds_t nfds, const struct timespec *restrict timeout, const sigset_t *restrict sigmask);

The poll( ) function provides applications with a mechanism for multiplexing input/output over a set of file descriptors. For each member of the array pointed to by fds, poll( ) shall examine the given file descriptor for the event(s) specified in events. The number of pollfd structures in the fds array is specified by nfds. The poll( ) function shall identify those file descriptors on which an application can read or write data, or on which certain events have occurred.

The ppoll( ) function provides applications with a mechanism for multiplexing input/output over a set of file descriptors. For each member of the array pointed to by fds, ppoll( ) shall examine the given file descriptor for the event(s) specified in events. The number of pollfd structures in the fds array is specified by nfds. The ppoll( ) function shall identify those file descriptors on which an application can read or write data, or on which certain events have occurred.

The poll( ) function shall be equivalent to the ppoll( ) function, except as follows:
• For the poll( ) function, the timeout period is given in milliseconds in an argument of type int, whereas for the ppoll( ) function the timeout period is given in seconds and nanoseconds in an argument of type struct timespec. A timeout of -1 for poll( ) is equivalent to passing a null pointer for the timeout for ppoll( ).
• The poll( ) function has no sigmask argument; it shall behave as ppoll( ) does when sigmask is a null pointer.

If none of the defined events have occurred on any selected file descriptor, poll( ) shall wait at least timeout milliseconds for an event to occur on any of the selected file descriptors. If the value of timeout is 0, poll( ) shall return immediately. If the value of timeout is −1, poll( ) shall block until a requested event occurs or until the call is interrupted.
Implementations may place limitations on the granularity

The timeout parameter controls how long the poll( ) or ppoll( ) function shall take before timing out. If the timeout parameter is positive for poll( ) or not a null pointer for ppoll( ), it specifies a maximum interval to wait for the poll to complete. If the specified time interval expires without any requested operation becoming ready, the function shall return. If the timeout parameter is -1 for poll( ) or a null pointer for ppoll( ), then the call shall block indefinitely until at least one descriptor meets the specified criteria. To effect a poll, the timeout parameter should be 0 for poll( ), or for ppoll( ) should not be a null pointer, and should point to a zero-valued timespec structure.
Implementations may place limitations on the maximum timeout interval supported. All implementations shall support a maximum timeout interval of at least 31 days for ppoll( ). If the timeout argument specifies a timeout interval greater than the implementation-defined maximum value, the maximum value shall be used as the actual timeout value. Implementations may also place limitations on the granularity

If sigmask is not a null pointer, then the ppoll( ) function shall replace the signal mask of the caller by the set of signals pointed to by sigmask before examining the descriptors, and shall restore the signal mask of the calling thread before returning.

If a thread gets canceled during a ppoll( ) call, the signal mask in effect when executing the registered cleanup functions is either the original signal mask or the signal mask installed as part of the ppoll( ) call.

The ppoll( ) function shall fail if:
[EINVAL] An invalid timeout interval was specified.

None.

Other than the difference in the precision of the timeout argument, the following ppoll( ) call:
<code>ready = ppoll(&fds, nfds, tmo_p, &sigmask);</code>
is equivalent to atomically executing the following calls:
<code>sigset_t origmask;
int timeout;

timeout = (tmo_p == NULL) ? -1 :
  (tmo_p->tv_sec * 1000 + tmo_p->tv_nsec / 1000000);
pthread_sigmask(SIG_SETMASK, &sigmask, &origmask);
ready = poll(&fds, nfds, timeout);
pthread_sigmask(SIG_SETMASK, &origmask, NULL);</code>

Code which wants to avoid the ambiguity of the signal mask for thread cancellation handlers can install an additional cancellation handler which resets the signal mask to the expected value.
<code>void cleanup(void *arg)
{
  sigset_t *ss = (sigset_t *) arg;
  pthread_sigmask(SIG_SETMASK, ss, NULL);
}
int call_ppoll(struct pollfd fds[], nfds_t nfds, const struct timespec *restrict timeout, const sigset_t *restrict sigmask)
{
  sigset_t oldmask;
  int result;
  pthread_sigmask(SIG_SETMASK, NULL, &oldmask);
  pthread_cleanup_push(cleanup, &oldmask);
  result = ppoll(fds, nfds, timeout, sigmask);
  pthread_cleanup_pop(0);
  return result;
}</code>

None.

The use of select( ) and pselect( ) requires that the application construct the set of fds to work on each time through a polling loop, and is inherently limited from operating on file descriptors larger than FD_SETSIZE. Also, the amount of work to perform scales as nfds increases, even if the number of file descriptors selected within the larger set remains the same. Thus, applications may wish to consider using poll( ) and ppoll( ) instead, for better scaling.

NAME
ppoll select — input/output multiplexing
SYNOPSIS
#include <poll.h>
int ppoll(struct pollfd [], nfds_t, const struct timespec *restrict, const sigset_t *restrict);
DESCRIPTION
Refer to poll( ).