[openvswitch] / lib / poll-loop.c

/* Copyright (c) 2008 The Board of Trustees of The Leland Stanford
 * Junior University
 * 
 * We are making the OpenFlow specification and associated documentation
 * (Software) available for public use and benefit with the expectation
 * that others will use, modify and enhance the Software and contribute
 * those enhancements back to the community. However, since we would
 * like to make the Software available for broadest use, with as few
 * restrictions as possible permission is hereby granted, free of
 * charge, to any person obtaining a copy of this Software to deal in
 * the Software under the copyrights without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 * 
 * The name and trademarks of copyright holder(s) may NOT be used in
 * advertising or publicity pertaining to the Software or any
 * derivatives without specific, written prior permission.
 */

#include "poll-loop.h"
#include <assert.h>
#include <errno.h>
#include <poll.h>
#include <stdlib.h>
#include <string.h>
#include "list.h"

#define THIS_MODULE VLM_poll_loop
#include "vlog.h"

/* An event that will wake the following call to poll_block(). */
struct poll_waiter {
    /* Set when the waiter is created. */
    struct list node;           /* Element in global waiters list. */
    int fd;                     /* File descriptor. */
    short int events;           /* Events to wait for (POLLIN, POLLOUT). */
    poll_fd_func *function;     /* Callback function, if any, or null. */
    void *aux;                  /* Argument to callback function. */

    /* Set only when poll_block() is called. */
    struct pollfd *pollfd;      /* Pointer to element of the pollfds array
                                   (null if added from a callback). */
};

/* All active poll waiters. */
static struct list waiters = LIST_INITIALIZER(&waiters);

/* Number of elements in the waiters list. */
static size_t n_waiters;

/* Max time to wait in next call to poll_block(), in milliseconds, or -1 to
 * wait forever. */
static int timeout = -1;

/* Callback currently running, to allow verifying that poll_cancel() is not
 * being called on a running callback. */
#ifndef NDEBUG
static struct poll_waiter *running_cb;
#endif

static struct poll_waiter *new_waiter(int fd, short int events);

/* Registers 'fd' as waiting for the specified 'events' (which should be POLLIN
 * or POLLOUT or POLLIN | POLLOUT).  The following call to poll_block() will
 * wake up when 'fd' becomes ready for one or more of the requested events.
 *
 * The event registration is one-shot: only the following call to poll_block()
 * is affected.  The event will need to be re-registered after poll_block() is
 * called if it is to persist. */
struct poll_waiter *
poll_fd_wait(int fd, short int events)
{
    return new_waiter(fd, events);
}

/* Causes the following call to poll_block() to block for no more than 'msec'
 * milliseconds.  If 'msec' is nonpositive, the following call to poll_block()
 * will not block at all.
 *
 * The timer registration is one-shot: only the following call to poll_block()
 * is affected.  The timer will need to be re-registered after poll_block() is
 * called if it is to persist. */
void
poll_timer_wait(int msec)
{
    if (timeout < 0 || msec < timeout) {
        timeout = MAX(0, msec);
    }
}

/* Causes the following call to poll_block() to wake up immediately, without
 * blocking. */
void
poll_immediate_wake(void)
{
    timeout = 0;
}

/* Blocks until one or more of the events registered with poll_fd_wait()
 * occurs, or until the minimum duration registered with poll_timer_wait()
 * elapses, or not at all if poll_immediate_wake() has been called.
 *
 * Also executes any autonomous subroutines registered with poll_fd_callback(),
 * if their file descriptor have become ready. */
void
poll_block(void)
{
    static struct pollfd *pollfds;
    static size_t max_pollfds;

    struct poll_waiter *pw;
    struct list *node;
    int n_pollfds;
    int retval;

    assert(!running_cb);
    if (max_pollfds < n_waiters) {
        max_pollfds = n_waiters;
        pollfds = xrealloc(pollfds, max_pollfds * sizeof *pollfds);
    }

    n_pollfds = 0;
    LIST_FOR_EACH (pw, struct poll_waiter, node, &waiters) {
        pw->pollfd = &pollfds[n_pollfds];
        pollfds[n_pollfds].fd = pw->fd;
        pollfds[n_pollfds].events = pw->events;
        pollfds[n_pollfds].revents = 0;
        n_pollfds++;
    }

    do {
        retval = poll(pollfds, n_pollfds, timeout);
    } while (retval < 0 && errno == EINTR);
    if (retval < 0) {
        VLOG_ERR("poll: %s", strerror(errno));
    }

    for (node = waiters.next; node != &waiters; ) {
        pw = CONTAINER_OF(node, struct poll_waiter, node);
        if (!pw->pollfd || !pw->pollfd->revents) {
            if (pw->function) {
                node = node->next;
                continue;
            }
        } else if (pw->function) {
#ifndef NDEBUG
            running_cb = pw;
#endif
            pw->function(pw->fd, pw->pollfd->revents, pw->aux);
#ifndef NDEBUG
            running_cb = NULL;
#endif
        }
        node = node->next;
        poll_cancel(pw);
    }

    timeout = -1;
}

/* Registers 'function' to be called with argument 'aux' by poll_block() when
 * 'fd' becomes ready for one of the events in 'events', which should be POLLIN
 * or POLLOUT or POLLIN | POLLOUT.
 *
 * The callback registration persists until the event actually occurs.  At that
 * point, it is automatically de-registered.  The callback function must
 * re-register the event by calling poll_fd_callback() again within the
 * callback, if it wants to be called back again later. */
struct poll_waiter *
poll_fd_callback(int fd, short int events, poll_fd_func *function, void *aux)
{
    struct poll_waiter *pw = new_waiter(fd, events);
    pw->function = function;
    pw->aux = aux;
    return pw;
}

/* Cancels the file descriptor event registered with poll_fd_wait() or
 * poll_fd_callback().  'pw' must be the struct poll_waiter returned by one of
 * those functions.
 *
 * An event registered with poll_fd_wait() may be canceled from its time of
 * registration until the next call to poll_block().  At that point, the event
 * is automatically canceled by the system and its poll_waiter is freed.
 *
 * An event registered with poll_fd_callback() may be canceled from its time of
 * registration until its callback is actually called.  At that point, the
 * event is automatically canceled by the system and its poll_waiter is
 * freed. */
void
poll_cancel(struct poll_waiter *pw)
{
    if (pw) {
        assert(pw != running_cb);
        list_remove(&pw->node);
        free(pw);
        n_waiters--;
    }
}
\f
/* Creates and returns a new poll_waiter for 'fd' and 'events'. */
static struct poll_waiter *
new_waiter(int fd, short int events)
{
    struct poll_waiter *waiter = xcalloc(1, sizeof *waiter);
    assert(fd >= 0);
    waiter->fd = fd;
    waiter->events = events;
    list_push_back(&waiters, &waiter->node);
    n_waiters++;
    return waiter;
}