/* Copyright Joyent, Inc. and other Node contributors. All rights reserved.

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to

 * deal in the Software 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.

 */

/* This file contains both the uv__async internal infrastructure and the

 * user-facing uv_async_t functions.

 */

#include "uv.h"

#include "internal.h"

#include "atomic-ops.h"

#include <errno.h>

#include <stdio.h>  /* snprintf() */

#include <assert.h>

#include <stdlib.h>

#include <string.h>

#include <unistd.h>

#include <sched.h>  /* sched_yield() */

#ifdef __linux__

#include <sys/eventfd.h>

#endif

static void uv__async_send(uv_loop_t* loop);

static int uv__async_start(uv_loop_t* loop);

int uv_async_init(uv_loop_t* loop, uv_async_t* handle, uv_async_cb async_cb) {

  int err;

  err = uv__async_start(loop);

  if (err)

    return err;

  uv__handle_init(loop, (uv_handle_t*)handle, UV_ASYNC);

  handle->async_cb = async_cb;

  handle->pending = 0;

  QUEUE_INSERT_TAIL(&loop->async_handles, &handle->queue);

  uv__handle_start(handle);

  return 0;

}

int uv_async_send(uv_async_t* handle) {

  /* Do a cheap read first. */

  if (ACCESS_ONCE(int, handle->pending) != 0)

    return 0;

  /* Tell the other thread we're busy with the handle. */

  if (cmpxchgi(&handle->pending, 0, 1) != 0)

    return 0;

  /* Wake up the other thread's event loop. */

  uv__async_send(handle->loop);

  /* Tell the other thread we're done. */

  if (cmpxchgi(&handle->pending, 1, 2) != 1)

    abort();

  return 0;

}

/* Only call this from the event loop thread. */

static int uv__async_spin(uv_async_t* handle) {

  int i;

  int rc;

  for (;;) {

    /* 997 is not completely chosen at random. It's a prime number, acyclical

     * by nature, and should therefore hopefully dampen sympathetic resonance.

     */

    for (i = 0; i < 997; i++) {

      /* rc=0 -- handle is not pending.

       * rc=1 -- handle is pending, other thread is still working with it.

       * rc=2 -- handle is pending, other thread is done.

       */

      rc = cmpxchgi(&handle->pending, 2, 0);

      if (rc != 1)

        return rc;

      /* Other thread is busy with this handle, spin until it's done. */

      cpu_relax();

    }

    /* Yield the CPU. We may have preempted the other thread while it's

     * inside the critical section and if it's running on the same CPU

     * as us, we'll just burn CPU cycles until the end of our time slice.

     */

    sched_yield();

  }

}

void uv__async_close(uv_async_t* handle) {

  uv__async_spin(handle);

  QUEUE_REMOVE(&handle->queue);

  uv__handle_stop(handle);

}

static void uv__async_io(uv_loop_t* loop, uv__io_t* w, unsigned int events) {

  char buf[1024];

  ssize_t r;

  QUEUE queue;

  QUEUE* q;

  uv_async_t* h;

  assert(w == &loop->async_io_watcher);

  for (;;) {

    r = read(w->fd, buf, sizeof(buf));

    if (r == sizeof(buf))

      continue;

    if (r != -1)

      break;

    if (errno == EAGAIN || errno == EWOULDBLOCK)

      break;

    if (errno == EINTR)

      continue;

    abort();

  }

  QUEUE_MOVE(&loop->async_handles, &queue);

  while (!QUEUE_EMPTY(&queue)) {

    q = QUEUE_HEAD(&queue);

    h = QUEUE_DATA(q, uv_async_t, queue);

    QUEUE_REMOVE(q);

    QUEUE_INSERT_TAIL(&loop->async_handles, q);

    if (0 == uv__async_spin(h))

      continue;  /* Not pending. */

    if (h->async_cb == NULL)

      continue;

    h->async_cb(h);

  }

}

static void uv__async_send(uv_loop_t* loop) {

  const void* buf;

  ssize_t len;

  int fd;

  int r;

  buf = "";

  len = 1;

  fd = loop->async_wfd;

#if defined(__linux__)

  if (fd == -1) {

    static const uint64_t val = 1;

    buf = &val;

    len = sizeof(val);

    fd = loop->async_io_watcher.fd;  /* eventfd */

  }

#endif

  do

    r = write(fd, buf, len);

  while (r == -1 && errno == EINTR);

  if (r == len)

    return;

  if (r == -1)

    if (errno == EAGAIN || errno == EWOULDBLOCK)

      return;

  abort();

}

static int uv__async_start(uv_loop_t* loop) {

  int pipefd[2];

  int err;

  if (loop->async_io_watcher.fd != -1)

    return 0;

#ifdef __linux__

  err = eventfd(0, EFD_CLOEXEC | EFD_NONBLOCK);

  if (err < 0)

    return UV__ERR(errno);

  pipefd[0] = err;

  pipefd[1] = -1;

#else

  err = uv__make_pipe(pipefd, UV__F_NONBLOCK);

  if (err < 0)

    return err;

#endif

  uv__io_init(&loop->async_io_watcher, uv__async_io, pipefd[0]);

  uv__io_start(loop, &loop->async_io_watcher, POLLIN);

  loop->async_wfd = pipefd[1];

  return 0;

}

int uv__async_fork(uv_loop_t* loop) {

  if (loop->async_io_watcher.fd == -1) /* never started */

    return 0;

  uv__async_stop(loop);

  return uv__async_start(loop);

}

void uv__async_stop(uv_loop_t* loop) {

  if (loop->async_io_watcher.fd == -1)

    return;

  if (loop->async_wfd != -1) {

    if (loop->async_wfd != loop->async_io_watcher.fd)

      uv__close(loop->async_wfd);

    loop->async_wfd = -1;

  }

  uv__io_stop(loop, &loop->async_io_watcher, POLLIN);

  uv__close(loop->async_io_watcher.fd);

  loop->async_io_watcher.fd = -1;

}