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IDProjectCategoryView StatusLast Update
0000209LDMudNetworkingpublic2004-11-26 22:55
ReporterlarsAssigned To 
Status newResolutionopen 
Summary0000209: Use poll() or kevents instead of select()
DescriptionShort: Use poll() instead of select()
Date: 980816
From: Lynx
Type: Feature
State: Acknowledged

poll() scales better for a large number of users, but is not implemented

See CUJ 2002/12 which presents a wrapper around poll(), /dev/poll and the (imo
superior) FreeBSD kqueues.

Implementation maybe by simulation poll() through select() where not


       poll - I/O multiplexing

       #include <poll.h>

       int poll(fds, nfds, timeout)
       struct pollfd *fds;
       unsigned long nfds;
       int timeout;

       poll() provides users with a mechanism for multiplexing
       input/output over a set of file descriptors (see
       intro(2)). poll() identifies those file descriptors on
       which a user can send or receive messages, or on which
       certain events have occurred. A user can receive messages
       using read(2V) or getmsg(2) and can send messages using
       write(2V) and putmsg(2). Certain ioctl(2) calls, such as
       I_RECVFD and I_SENDFD (see streamio(4)), can also be used
       to receive and send messages on streams.

       fds specifies the file descriptors to be examined and the
       events of interest for each file descriptor. It is a
       pointer to an array with one element for each open file
       descriptor of interest. The array's elements are pollfd
       structures which contain the following members:

              int fd; /* file descriptor */
              short events; /* requested events */
              short revents; /* returned events */

       where fd specifies an open file descriptor and events and
       revents are bitmasks constructed by ORing any combination
       of the following event flags:

       POLLIN If the file descriptor refers to a stream,
                      a non-priority or file descriptor passing
                      message (see I_RECVFD) is present on the
                      stream head read queue. This flag is set
                      even if the message is of zero length. If
                      the file descriptor is not a stream, the
                      file descriptor is readable. In revents,
                      this flag is mutually exclusive with POLL?

       POLLPRI If the file descriptor is a stream, a pri?
                      ority message is present on the stream head
                      read queue. This flag is set even if the
                      message is of zero length. If the file
                      descriptor is not a stream, some excep?
                      tional condition has occurred. In revents,
                      this flag is mutually exclusive with

                         21 January 1990 1


       POLLOUT If the file descriptor is a stream, the
                      first downstream write queue in the stream
                      is not full. Priority control messages can
                      be sent (see putmsg(2)) at any time. If
                      the file descriptor is not a stream, it is

       POLLERR If the file descriptor is a stream, an
                      error message has arrived at the stream
                      head. This flag is only valid in the
                      revents bitmask; it is not used in the
                      events field.

       POLLHUP If the file descriptor is a stream, a
                      hangup has occurred on the stream. This
                      event and POLLOUT are mutually exclusive; a
                      stream can never be writable if a hangup
                      has occurred. However, this event and
                      POLLIN or POLLPRI are not mutually exclu?
                      sive. This flag is only valid in the
                      revents bitmask; it is not used in the
                      events field.

       POLLNVAL The specified fd value does not specify an
                      open file descriptor. This flag is only
                      valid in the revents field; it is not used
                      in the events field.

       For each element of the array pointed to by fds, poll()
       examines the given file descriptor for the event(s) speci?
       fied in events. The number of file descriptors to be
       examined is specified by nfds. If nfds exceeds the system
       limit of open files (see getdtablesize(2)), poll() will

       If the value fd is less than zero, events is ignored and
       revents is set to 0 in that entry on return from poll().

       The results of the poll() query are stored in the revents
       field in the pollfd structure. Bits are set in the
       revents bitmask to indicate which of the requested events
       are true. If none are true, none of the specified bits is
       set in revents when the poll() call returns. The event
       flags POLLHUP, POLLERR, and POLLNVAL are always set in
       revents if the conditions they indicate are true; this
       occurs even though these flags were not present in events.

       If none of the defined events have occurred on any
       selected file descriptor, poll() waits at least timeout
       milliseconds for an event to occur on any of the selected
       file descriptors. On a computer where millisecond timing
       accuracy is not available, timeout is rounded up to the
       nearest legal value available on that system. If the
       value timeout is 0, poll() returns immediately. If the

                         21 January 1990 2


       value of timeout is -1, poll() blocks until a requested
       event occurs or until the call is interrupted. poll() is
       not affected by the O_NDELAY flag.

       poll() returns a non-negative value on success. A posi?
       tive value indicates the total number of file descriptors
       that has been selected (for instance, file descriptors for
       which the revents field is non-zero). 0 indicates the
       call timed out and no file descriptors have been selected.
       On failure, poll() returns -1 and sets errno to indicate
       the error.

       EAGAIN Allocation of internal data structures
                      failed, but the request should be attempted

       EFAULT Some argument points outside the allocated
                      address space.

       EINTR A signal was caught during the poll() sys?
                      tem call.

       EINVAL The argument nfds is less than zero.

                      nfds is greater than the system limit of
                      open files.

       getdtablesize(2), getmsg(2), intro(2), ioctl(2),
       putmsg(2), read(2V), select(2), write(2V), streamio(4)
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Issue History

Date Modified Username Field Change
2004-11-26 22:55 lars New Issue