/*
 *
 * Copyright 2015-2016, Google Inc.
 * All rights reserved.
 *
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 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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 */

#include <grpc/support/port_platform.h>

#ifdef GPR_LINUX_MULTIPOLL_WITH_EPOLL

#include <errno.h>
#include <poll.h>
#include <string.h>
#include <sys/epoll.h>
#include <unistd.h>

#include <grpc/support/alloc.h>
#include <grpc/support/log.h>
#include <grpc/support/useful.h>
#include "src/core/lib/iomgr/fd_posix.h"
#include "src/core/lib/iomgr/pollset_posix.h"
#include "src/core/lib/profiling/timers.h"
#include "src/core/lib/support/block_annotate.h"

struct epoll_fd_list {
  int *epoll_fds;
  size_t count;
  size_t capacity;
};

static struct epoll_fd_list epoll_fd_global_list;
static gpr_once init_epoll_fd_list_mu = GPR_ONCE_INIT;
static gpr_mu epoll_fd_list_mu;

static void init_mu(void) { gpr_mu_init(&epoll_fd_list_mu); }

static void add_epoll_fd_to_global_list(int epoll_fd) {
  gpr_once_init(&init_epoll_fd_list_mu, init_mu);

  gpr_mu_lock(&epoll_fd_list_mu);
  if (epoll_fd_global_list.count == epoll_fd_global_list.capacity) {
    epoll_fd_global_list.capacity =
        GPR_MAX((size_t)8, epoll_fd_global_list.capacity * 2);
    epoll_fd_global_list.epoll_fds =
        gpr_realloc(epoll_fd_global_list.epoll_fds,
                    epoll_fd_global_list.capacity * sizeof(int));
  }
  epoll_fd_global_list.epoll_fds[epoll_fd_global_list.count++] = epoll_fd;
  gpr_mu_unlock(&epoll_fd_list_mu);
}

static void remove_epoll_fd_from_global_list(int epoll_fd) {
  gpr_mu_lock(&epoll_fd_list_mu);
  GPR_ASSERT(epoll_fd_global_list.count > 0);
  for (size_t i = 0; i < epoll_fd_global_list.count; i++) {
    if (epoll_fd == epoll_fd_global_list.epoll_fds[i]) {
      epoll_fd_global_list.epoll_fds[i] =
          epoll_fd_global_list.epoll_fds[--(epoll_fd_global_list.count)];
      break;
    }
  }
  gpr_mu_unlock(&epoll_fd_list_mu);
}

void grpc_remove_fd_from_all_epoll_sets(int fd) {
  int err;
  gpr_once_init(&init_epoll_fd_list_mu, init_mu);
  gpr_mu_lock(&epoll_fd_list_mu);
  if (epoll_fd_global_list.count == 0) {
    gpr_mu_unlock(&epoll_fd_list_mu);
    return;
  }
  for (size_t i = 0; i < epoll_fd_global_list.count; i++) {
    err = epoll_ctl(epoll_fd_global_list.epoll_fds[i], EPOLL_CTL_DEL, fd, NULL);
    if (err < 0 && errno != ENOENT) {
      gpr_log(GPR_ERROR, "epoll_ctl del for %d failed: %s", fd,
              strerror(errno));
    }
  }
  gpr_mu_unlock(&epoll_fd_list_mu);
}

typedef struct {
  grpc_pollset *pollset;
  grpc_fd *fd;
  grpc_closure closure;
} delayed_add;

typedef struct { int epoll_fd; } pollset_hdr;

static void finally_add_fd(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
                           grpc_fd *fd) {
  pollset_hdr *h = pollset->data.ptr;
  struct epoll_event ev;
  int err;
  grpc_fd_watcher watcher;

  /* We pretend to be polling whilst adding an fd to keep the fd from being
     closed during the add. This may result in a spurious wakeup being assigned
     to this pollset whilst adding, but that should be benign. */
  GPR_ASSERT(grpc_fd_begin_poll(fd, pollset, NULL, 0, 0, &watcher) == 0);
  if (watcher.fd != NULL) {
    ev.events = (uint32_t)(EPOLLIN | EPOLLOUT | EPOLLET);
    ev.data.ptr = fd;
    err = epoll_ctl(h->epoll_fd, EPOLL_CTL_ADD, fd->fd, &ev);
    if (err < 0) {
      /* FDs may be added to a pollset multiple times, so EEXIST is normal. */
      if (errno != EEXIST) {
        gpr_log(GPR_ERROR, "epoll_ctl add for %d failed: %s", fd->fd,
                strerror(errno));
      }
    }
  }
  grpc_fd_end_poll(exec_ctx, &watcher, 0, 0);
}

static void perform_delayed_add(grpc_exec_ctx *exec_ctx, void *arg,
                                bool iomgr_status) {
  delayed_add *da = arg;

  if (!grpc_fd_is_orphaned(da->fd)) {
    finally_add_fd(exec_ctx, da->pollset, da->fd);
  }

  gpr_mu_lock(&da->pollset->mu);
  da->pollset->in_flight_cbs--;
  if (da->pollset->shutting_down) {
    /* We don't care about this pollset anymore. */
    if (da->pollset->in_flight_cbs == 0 && !da->pollset->called_shutdown) {
      da->pollset->called_shutdown = 1;
      grpc_exec_ctx_enqueue(exec_ctx, da->pollset->shutdown_done, true, NULL);
    }
  }
  gpr_mu_unlock(&da->pollset->mu);

  GRPC_FD_UNREF(da->fd, "delayed_add");

  gpr_free(da);
}

static void multipoll_with_epoll_pollset_add_fd(grpc_exec_ctx *exec_ctx,
                                                grpc_pollset *pollset,
                                                grpc_fd *fd,
                                                int and_unlock_pollset) {
  if (and_unlock_pollset) {
    gpr_mu_unlock(&pollset->mu);
    finally_add_fd(exec_ctx, pollset, fd);
  } else {
    delayed_add *da = gpr_malloc(sizeof(*da));
    da->pollset = pollset;
    da->fd = fd;
    GRPC_FD_REF(fd, "delayed_add");
    grpc_closure_init(&da->closure, perform_delayed_add, da);
    pollset->in_flight_cbs++;
    grpc_exec_ctx_enqueue(exec_ctx, &da->closure, true, NULL);
  }
}

/* TODO(klempner): We probably want to turn this down a bit */
#define GRPC_EPOLL_MAX_EVENTS 1000

static void multipoll_with_epoll_pollset_maybe_work_and_unlock(
    grpc_exec_ctx *exec_ctx, grpc_pollset *pollset, grpc_pollset_worker *worker,
    gpr_timespec deadline, gpr_timespec now) {
  struct epoll_event ep_ev[GRPC_EPOLL_MAX_EVENTS];
  int ep_rv;
  int poll_rv;
  pollset_hdr *h = pollset->data.ptr;
  int timeout_ms;
  struct pollfd pfds[2];

  /* If you want to ignore epoll's ability to sanely handle parallel pollers,
   * for a more apples-to-apples performance comparison with poll, add a
   * if (pollset->counter != 0) { return 0; }
   * here.
   */

  gpr_mu_unlock(&pollset->mu);

  timeout_ms = grpc_poll_deadline_to_millis_timeout(deadline, now);

  pfds[0].fd = GRPC_WAKEUP_FD_GET_READ_FD(&worker->wakeup_fd->fd);
  pfds[0].events = POLLIN;
  pfds[0].revents = 0;
  pfds[1].fd = h->epoll_fd;
  pfds[1].events = POLLIN;
  pfds[1].revents = 0;

  /* TODO(vpai): Consider first doing a 0 timeout poll here to avoid
     even going into the blocking annotation if possible */
  GPR_TIMER_BEGIN("poll", 0);
  GRPC_SCHEDULING_START_BLOCKING_REGION;
  poll_rv = grpc_poll_function(pfds, 2, timeout_ms);
  GRPC_SCHEDULING_END_BLOCKING_REGION;
  GPR_TIMER_END("poll", 0);

  if (poll_rv < 0) {
    if (errno != EINTR) {
      gpr_log(GPR_ERROR, "poll() failed: %s", strerror(errno));
    }
  } else if (poll_rv == 0) {
    /* do nothing */
  } else {
    if (pfds[0].revents) {
      grpc_wakeup_fd_consume_wakeup(&worker->wakeup_fd->fd);
    }
    if (pfds[1].revents) {
      do {
        /* The following epoll_wait never blocks; it has a timeout of 0 */
        ep_rv = epoll_wait(h->epoll_fd, ep_ev, GRPC_EPOLL_MAX_EVENTS, 0);
        if (ep_rv < 0) {
          if (errno != EINTR) {
            gpr_log(GPR_ERROR, "epoll_wait() failed: %s", strerror(errno));
          }
        } else {
          int i;
          for (i = 0; i < ep_rv; ++i) {
            grpc_fd *fd = ep_ev[i].data.ptr;
            /* TODO(klempner): We might want to consider making err and pri
             * separate events */
            int cancel = ep_ev[i].events & (EPOLLERR | EPOLLHUP);
            int read_ev = ep_ev[i].events & (EPOLLIN | EPOLLPRI);
            int write_ev = ep_ev[i].events & EPOLLOUT;
            if (fd == NULL) {
              grpc_wakeup_fd_consume_wakeup(&grpc_global_wakeup_fd);
            } else {
              if (read_ev || cancel) {
                grpc_fd_become_readable(exec_ctx, fd);
              }
              if (write_ev || cancel) {
                grpc_fd_become_writable(exec_ctx, fd);
              }
            }
          }
        }
      } while (ep_rv == GRPC_EPOLL_MAX_EVENTS);
    }
  }
}

static void multipoll_with_epoll_pollset_finish_shutdown(
    grpc_pollset *pollset) {}

static void multipoll_with_epoll_pollset_destroy(grpc_pollset *pollset) {
  pollset_hdr *h = pollset->data.ptr;
  close(h->epoll_fd);
  remove_epoll_fd_from_global_list(h->epoll_fd);
  gpr_free(h);
}

static const grpc_pollset_vtable multipoll_with_epoll_pollset = {
    multipoll_with_epoll_pollset_add_fd,
    multipoll_with_epoll_pollset_maybe_work_and_unlock,
    multipoll_with_epoll_pollset_finish_shutdown,
    multipoll_with_epoll_pollset_destroy};

static void epoll_become_multipoller(grpc_exec_ctx *exec_ctx,
                                     grpc_pollset *pollset, grpc_fd **fds,
                                     size_t nfds) {
  size_t i;
  pollset_hdr *h = gpr_malloc(sizeof(pollset_hdr));
  struct epoll_event ev;
  int err;

  pollset->vtable = &multipoll_with_epoll_pollset;
  pollset->data.ptr = h;
  h->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
  if (h->epoll_fd < 0) {
    /* TODO(klempner): Fall back to poll here, especially on ENOSYS */
    gpr_log(GPR_ERROR, "epoll_create1 failed: %s", strerror(errno));
    abort();
  }
  add_epoll_fd_to_global_list(h->epoll_fd);

  ev.events = (uint32_t)(EPOLLIN | EPOLLET);
  ev.data.ptr = NULL;
  err = epoll_ctl(h->epoll_fd, EPOLL_CTL_ADD,
                  GRPC_WAKEUP_FD_GET_READ_FD(&grpc_global_wakeup_fd), &ev);
  if (err < 0) {
    gpr_log(GPR_ERROR, "epoll_ctl add for %d failed: %s",
            GRPC_WAKEUP_FD_GET_READ_FD(&grpc_global_wakeup_fd),
            strerror(errno));
  }

  for (i = 0; i < nfds; i++) {
    multipoll_with_epoll_pollset_add_fd(exec_ctx, pollset, fds[i], 0);
  }
}

grpc_platform_become_multipoller_type grpc_platform_become_multipoller =
    epoll_become_multipoller;

#else /* GPR_LINUX_MULTIPOLL_WITH_EPOLL */

void grpc_remove_fd_from_all_epoll_sets(int fd) {}

#endif /* GPR_LINUX_MULTIPOLL_WITH_EPOLL */