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    The following form allows you to view linux man pages.

    Command:

    ppoll

    
    
    

    SYNOPSIS

           #include <poll.h>
    
           int poll(struct pollfd *fds, nfds_t nfds, int timeout);
    
           #define _GNU_SOURCE         /* See feature_test_macros(7) */
           #include <poll.h>
    
           int ppoll(struct pollfd *fds, nfds_t nfds,
                   const struct timespec *timeout_ts, const sigset_t *sigmask);
    
    
    

    DESCRIPTION

           poll()  performs a similar task to select(2): it waits for one of a set
           of file descriptors to become ready to perform I/O.
    
           The set of file descriptors to be monitored is  specified  in  the  fds
           argument, which is an array of structures of the following form:
    
               struct pollfd {
                   int   fd;         /* file descriptor */
                   short events;     /* requested events */
                   short revents;    /* returned events */
               };
    
           The caller should specify the number of items in the fds array in nfds.
    
           The field fd contains a file descriptor for  an  open  file.   If  this
           field  is  negative, then the corresponding events field is ignored and
           the revents field returns zero.  (This provides an easy way of ignoring
           a  file  descriptor  for  a  single  poll()  call: simply negate the fd
           field.)
    
           The field events is an input  parameter,  a  bit  mask  specifying  the
           events  the  application  is  interested in for the file descriptor fd.
           This field may be specified as zero, in which case the only events that
           can  be  returned  in  revents  are POLLHUP, POLLERR, and POLLNVAL (see
           below).
    
           The field revents is an output parameter, filled by the kernel with the
           events  that  actually  occurred.   The  bits  returned  in revents can
           include any of those specified in events, or one of the values POLLERR,
           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, then  poll()  blocks  until  one  of  the  events
           occurs.
    
           The  timeout  argument specifies the number of milliseconds that poll()
           should block waiting for a file descriptor to become ready.   The  call
           will block until either:
           <poll.h>:
    
                  POLLIN There is data to read.
    
                  POLLPRI
                         There is urgent data to read (e.g., out-of-band  data  on
                         TCP socket; pseudoterminal master in packet mode has seen
                         state change in slave).
    
                  POLLOUT
                         Writing now will not block.
    
                  POLLRDHUP (since Linux 2.6.17)
                         Stream socket peer closed connection, or shut down  writ-
                         ing  half  of  connection.   The _GNU_SOURCE feature test
                         macro must be defined (before including any header files)
                         in order to obtain this definition.
    
                  POLLERR
                         Error condition (output only).
    
                  POLLHUP
                         Hang up (output only).
    
                  POLLNVAL
                         Invalid request: fd not open (output only).
    
           When  compiling with _XOPEN_SOURCE defined, one also has the following,
           which convey no further information beyond the bits listed above:
    
                  POLLRDNORM
                         Equivalent to POLLIN.
    
                  POLLRDBAND
                         Priority band data  can  be  read  (generally  unused  on
                         Linux).
    
                  POLLWRNORM
                         Equivalent to POLLOUT.
    
                  POLLWRBAND
                         Priority data may be written.
    
           Linux also knows about, but does not use POLLMSG.
    
       ppoll()
           The  relationship  between poll() and ppoll() is analogous to the rela-
           tionship between select(2) and  pselect(2):  like  pselect(2),  ppoll()
           allows  an  application  to  safely wait until either a file descriptor
           becomes ready or until a signal is caught.
    
           Other than the difference in the precision of the timeout argument, the
    
           See  the description of pselect(2) for an explanation of why ppoll() is
           necessary.
    
           If the sigmask argument is specified  as  NULL,  then  no  signal  mask
           manipulation is performed (and thus ppoll() differs from poll() only in
           the precision of the timeout argument).
    
           The timeout_ts argument specifies an upper limit on the amount of  time
           that  ppoll() will block.  This argument is a pointer to a structure of
           the following form:
    
               struct timespec {
                   long    tv_sec;         /* seconds */
                   long    tv_nsec;        /* nanoseconds */
               };
    
           If timeout_ts is specified as NULL,  then  ppoll()  can  block  indefi-
           nitely.
    
    
    

    RETURN VALUE

           On success, a positive number is returned; this is the number of struc-
           tures which have nonzero revents fields (in other words, those descrip-
           tors  with events or errors reported).  A value of 0 indicates that the
           call timed out and no file descriptors were ready.   On  error,  -1  is
           returned, and errno is set appropriately.
    
    
    

    ERRORS

           EFAULT The  array  given  as  argument was not contained in the calling
                  program's address space.
    
           EINTR  A signal occurred before any requested event; see signal(7).
    
           EINVAL The nfds value exceeds the RLIMIT_NOFILE value.
    
           ENOMEM There was no space to allocate file descriptor tables.
    
    
    

    VERSIONS

           The poll() system call was introduced in Linux 2.1.23.  On  older  ker-
           nels  that  lack  this  system call, the glibc (and the old Linux libc)
           poll() wrapper function provides emulation using select(2).
    
           The ppoll() system call was added  to  Linux  in  kernel  2.6.16.   The
           ppoll() library call was added in glibc 2.4.
    
    
    

    CONFORMING TO

           poll() conforms to POSIX.1-2001.  ppoll() is Linux-specific.
    
    
    

    NOTES

           Some  implementations  define  the nonstandard constant INFTIM with the
           value -1 for use as a timeout for poll().  This constant  is  not  pro-
           vided in glibc.
    
    
    

    SEE ALSO

           restart_syscall(2), select(2), select_tut(2), time(7)
    
    
    

    Linux 2014-01-31 POLL(2)

    
    
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