/*
 *
 * Copyright 2015, Google Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * 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
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

#include <grpc/support/port_platform.h>

#ifdef GPR_POSIX_SOCKET

#include "src/core/iomgr/pollset_posix.h"

#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "src/core/iomgr/alarm_internal.h"
#include "src/core/iomgr/fd_posix.h"
#include "src/core/iomgr/iomgr_internal.h"
#include "src/core/iomgr/socket_utils_posix.h"
#include "src/core/profiling/timers.h"
#include <grpc/support/alloc.h>
#include <grpc/support/log.h>
#include <grpc/support/thd.h>
#include <grpc/support/tls.h>
#include <grpc/support/useful.h>

GPR_TLS_DECL(g_current_thread_poller);
GPR_TLS_DECL(g_current_thread_worker);

grpc_poll_function_type grpc_poll_function = poll;

static void remove_worker(grpc_pollset *p, grpc_pollset_worker *worker) {
  worker->prev->next = worker->next;
  worker->next->prev = worker->prev;
}

int grpc_pollset_has_workers(grpc_pollset *p) {
  return p->root_worker.next != &p->root_worker;
}

static grpc_pollset_worker *pop_front_worker(grpc_pollset *p) {
  if (grpc_pollset_has_workers(p)) {
    grpc_pollset_worker *w = p->root_worker.next;
    remove_worker(p, w);
    return w;
  } else {
    return NULL;
  }
}

static void push_back_worker(grpc_pollset *p, grpc_pollset_worker *worker) {
  worker->next = &p->root_worker;
  worker->prev = worker->next->prev;
  worker->prev->next = worker->next->prev = worker;
}

static void push_front_worker(grpc_pollset *p, grpc_pollset_worker *worker) {
  worker->prev = &p->root_worker;
  worker->next = worker->prev->next;
  worker->prev->next = worker->next->prev = worker;
}

void grpc_pollset_kick(grpc_pollset *p, grpc_pollset_worker *specific_worker) {
  /* pollset->mu already held */
  if (specific_worker != NULL) {
    if (specific_worker == GRPC_POLLSET_KICK_BROADCAST) {
      for (specific_worker = p->root_worker.next;
           specific_worker != &p->root_worker;
           specific_worker = specific_worker->next) {
        grpc_wakeup_fd_wakeup(&specific_worker->wakeup_fd);
      }
      p->kicked_without_pollers = 1;
    } else if (gpr_tls_get(&g_current_thread_worker) !=
               (gpr_intptr)specific_worker) {
      grpc_wakeup_fd_wakeup(&specific_worker->wakeup_fd);
    }
  } else if (gpr_tls_get(&g_current_thread_poller) != (gpr_intptr)p) {
    specific_worker = pop_front_worker(p);
    if (specific_worker != NULL) {
      push_back_worker(p, specific_worker);
      grpc_wakeup_fd_wakeup(&specific_worker->wakeup_fd);
    } else {
      p->kicked_without_pollers = 1;
    }
  }
}

/* global state management */

void grpc_pollset_global_init(void) {
  gpr_tls_init(&g_current_thread_poller);
  grpc_wakeup_fd_global_init();
}

void grpc_pollset_global_shutdown(void) {
  gpr_tls_destroy(&g_current_thread_poller);
  grpc_wakeup_fd_global_destroy();
}

/* main interface */

static void become_basic_pollset(grpc_pollset *pollset, grpc_fd *fd_or_null);

void grpc_pollset_init(grpc_pollset *pollset) {
  gpr_mu_init(&pollset->mu);
  pollset->root_worker.next = pollset->root_worker.prev = &pollset->root_worker;
  pollset->in_flight_cbs = 0;
  pollset->shutting_down = 0;
  pollset->called_shutdown = 0;
  become_basic_pollset(pollset, NULL);
}

void grpc_pollset_add_fd(grpc_pollset *pollset, grpc_fd *fd) {
  gpr_mu_lock(&pollset->mu);
  pollset->vtable->add_fd(pollset, fd, 1);
/* the following (enabled only in debug) will reacquire and then release
   our lock - meaning that if the unlocking flag passed to del_fd above is
   not respected, the code will deadlock (in a way that we have a chance of
   debugging) */
#ifndef NDEBUG
  gpr_mu_lock(&pollset->mu);
  gpr_mu_unlock(&pollset->mu);
#endif
}

void grpc_pollset_del_fd(grpc_pollset *pollset, grpc_fd *fd) {
  gpr_mu_lock(&pollset->mu);
  pollset->vtable->del_fd(pollset, fd, 1);
/* the following (enabled only in debug) will reacquire and then release
   our lock - meaning that if the unlocking flag passed to del_fd above is
   not respected, the code will deadlock (in a way that we have a chance of
   debugging) */
#ifndef NDEBUG
  gpr_mu_lock(&pollset->mu);
  gpr_mu_unlock(&pollset->mu);
#endif
}

static void finish_shutdown(grpc_pollset *pollset) {
  pollset->vtable->finish_shutdown(pollset);
  pollset->shutdown_done_cb(pollset->shutdown_done_arg);
}

void grpc_pollset_work(grpc_pollset *pollset, grpc_pollset_worker *worker,
                       gpr_timespec now, gpr_timespec deadline) {
  /* pollset->mu already held */
  int added_worker = 0;
  /* this must happen before we (potentially) drop pollset->mu */
  worker->next = worker->prev = NULL;
  /* TODO(ctiller): pool these */
  grpc_wakeup_fd_init(&worker->wakeup_fd);
  if (grpc_maybe_call_delayed_callbacks(&pollset->mu, 1)) {
    goto done;
  }
  if (grpc_alarm_check(&pollset->mu, now, &deadline)) {
    goto done;
  }
  if (pollset->shutting_down) {
    goto done;
  }
  if (!pollset->kicked_without_pollers) {
    push_front_worker(pollset, worker);
    added_worker = 1;
    gpr_tls_set(&g_current_thread_poller, (gpr_intptr)pollset);
    pollset->vtable->maybe_work(pollset, worker, deadline, now, 1);
    gpr_tls_set(&g_current_thread_poller, 0);
  } else {
    pollset->kicked_without_pollers = 0;
  }
done:
  grpc_wakeup_fd_destroy(&worker->wakeup_fd);
  if (added_worker) {
    remove_worker(pollset, worker);
  }
  if (pollset->shutting_down) {
    if (grpc_pollset_has_workers(pollset)) {
      grpc_pollset_kick(pollset, NULL);
    } else if (!pollset->called_shutdown && pollset->in_flight_cbs == 0) {
      pollset->called_shutdown = 1;
      gpr_mu_unlock(&pollset->mu);
      finish_shutdown(pollset);
      /* Continuing to access pollset here is safe -- it is the caller's
       * responsibility to not destroy when it has outstanding calls to
       * grpc_pollset_work.
       * TODO(dklempner): Can we refactor the shutdown logic to avoid this? */
      gpr_mu_lock(&pollset->mu);
    }
  }
}

void grpc_pollset_shutdown(grpc_pollset *pollset,
                           void (*shutdown_done)(void *arg),
                           void *shutdown_done_arg) {
  int call_shutdown = 0;
  gpr_mu_lock(&pollset->mu);
  GPR_ASSERT(!pollset->shutting_down);
  pollset->shutting_down = 1;
  if (!pollset->called_shutdown && pollset->in_flight_cbs == 0 &&
      !grpc_pollset_has_workers(pollset)) {
    pollset->called_shutdown = 1;
    call_shutdown = 1;
  }
  pollset->shutdown_done_cb = shutdown_done;
  pollset->shutdown_done_arg = shutdown_done_arg;
  grpc_pollset_kick(pollset, GRPC_POLLSET_KICK_BROADCAST);
  gpr_mu_unlock(&pollset->mu);

  if (call_shutdown) {
    finish_shutdown(pollset);
  }
}

void grpc_pollset_destroy(grpc_pollset *pollset) {
  GPR_ASSERT(pollset->shutting_down);
  GPR_ASSERT(pollset->in_flight_cbs == 0);
  GPR_ASSERT(!grpc_pollset_has_workers(pollset));
  pollset->vtable->destroy(pollset);
  gpr_mu_destroy(&pollset->mu);
}

int grpc_poll_deadline_to_millis_timeout(gpr_timespec deadline,
                                         gpr_timespec now) {
  gpr_timespec timeout;
  static const int max_spin_polling_us = 10;
  if (gpr_time_cmp(deadline, gpr_inf_future(deadline.clock_type)) == 0) {
    return -1;
  }
  if (gpr_time_cmp(deadline, gpr_time_add(now, gpr_time_from_micros(
                                                   max_spin_polling_us,
                                                   GPR_TIMESPAN))) <= 0) {
    return 0;
  }
  timeout = gpr_time_sub(deadline, now);
  return gpr_time_to_millis(gpr_time_add(
      timeout, gpr_time_from_nanos(GPR_NS_PER_SEC - 1, GPR_TIMESPAN)));
}

/*
 * basic_pollset - a vtable that provides polling for zero or one file
 *                 descriptor via poll()
 */

typedef struct grpc_unary_promote_args {
  const grpc_pollset_vtable *original_vtable;
  grpc_pollset *pollset;
  grpc_fd *fd;
  grpc_iomgr_closure promotion_closure;
} grpc_unary_promote_args;

static void basic_do_promote(void *args, int success) {
  grpc_unary_promote_args *up_args = args;
  const grpc_pollset_vtable *original_vtable = up_args->original_vtable;
  grpc_pollset *pollset = up_args->pollset;
  grpc_fd *fd = up_args->fd;
  int do_shutdown_cb = 0;

  /*
   * This is quite tricky. There are a number of cases to keep in mind here:
   * 1. fd may have been orphaned
   * 2. The pollset may no longer be a unary poller (and we can't let case #1
   * leak to other pollset types!)
   * 3. pollset's fd (which may have changed) may have been orphaned
   * 4. The pollset may be shutting down.
   */

  gpr_mu_lock(&pollset->mu);
  /* First we need to ensure that nobody is polling concurrently */
  if (grpc_pollset_has_workers(pollset)) {
    grpc_pollset_kick(pollset, GRPC_POLLSET_KICK_BROADCAST);
    grpc_iomgr_add_callback(&up_args->promotion_closure);
    gpr_mu_unlock(&pollset->mu);
    return;
  }

  gpr_free(up_args);
  /* At this point the pollset may no longer be a unary poller. In that case
   * we should just call the right add function and be done. */
  /* TODO(klempner): If we're not careful this could cause infinite recursion.
   * That's not a problem for now because empty_pollset has a trivial poller
   * and we don't have any mechanism to unbecome multipoller. */
  pollset->in_flight_cbs--;
  if (pollset->shutting_down) {
    /* We don't care about this pollset anymore. */
    if (pollset->in_flight_cbs == 0 && !pollset->called_shutdown) {
      GPR_ASSERT(!grpc_pollset_has_workers(pollset));
      pollset->called_shutdown = 1;
      do_shutdown_cb = 1;
    }
  } else if (grpc_fd_is_orphaned(fd)) {
    /* Don't try to add it to anything, we'll drop our ref on it below */
  } else if (pollset->vtable != original_vtable) {
    pollset->vtable->add_fd(pollset, fd, 0);
  } else if (fd != pollset->data.ptr) {
    grpc_fd *fds[2];
    fds[0] = pollset->data.ptr;
    fds[1] = fd;

    if (fds[0] && !grpc_fd_is_orphaned(fds[0])) {
      grpc_platform_become_multipoller(pollset, fds, GPR_ARRAY_SIZE(fds));
      GRPC_FD_UNREF(fds[0], "basicpoll");
    } else {
      /* old fd is orphaned and we haven't cleaned it up until now, so remain a
       * unary poller */
      /* Note that it is possible that fds[1] is also orphaned at this point.
       * That's okay, we'll correct it at the next add or poll. */
      if (fds[0]) GRPC_FD_UNREF(fds[0], "basicpoll");
      pollset->data.ptr = fd;
      GRPC_FD_REF(fd, "basicpoll");
    }
  }

  gpr_mu_unlock(&pollset->mu);

  if (do_shutdown_cb) {
    pollset->shutdown_done_cb(pollset->shutdown_done_arg);
  }

  /* Matching ref in basic_pollset_add_fd */
  GRPC_FD_UNREF(fd, "basicpoll_add");
}

static void basic_pollset_add_fd(grpc_pollset *pollset, grpc_fd *fd,
                                 int and_unlock_pollset) {
  grpc_unary_promote_args *up_args;
  GPR_ASSERT(fd);
  if (fd == pollset->data.ptr) goto exit;

  if (!grpc_pollset_has_workers(pollset)) {
    /* Fast path -- no in flight cbs */
    /* TODO(klempner): Comment this out and fix any test failures or establish
     * they are due to timing issues */
    grpc_fd *fds[2];
    fds[0] = pollset->data.ptr;
    fds[1] = fd;

    if (fds[0] == NULL) {
      pollset->data.ptr = fd;
      GRPC_FD_REF(fd, "basicpoll");
    } else if (!grpc_fd_is_orphaned(fds[0])) {
      grpc_platform_become_multipoller(pollset, fds, GPR_ARRAY_SIZE(fds));
      GRPC_FD_UNREF(fds[0], "basicpoll");
    } else {
      /* old fd is orphaned and we haven't cleaned it up until now, so remain a
       * unary poller */
      GRPC_FD_UNREF(fds[0], "basicpoll");
      pollset->data.ptr = fd;
      GRPC_FD_REF(fd, "basicpoll");
    }
    goto exit;
  }

  /* Now we need to promote. This needs to happen when we're not polling. Since
   * this may be called from poll, the wait needs to happen asynchronously. */
  GRPC_FD_REF(fd, "basicpoll_add");
  pollset->in_flight_cbs++;
  up_args = gpr_malloc(sizeof(*up_args));
  up_args->pollset = pollset;
  up_args->fd = fd;
  up_args->original_vtable = pollset->vtable;
  up_args->promotion_closure.cb = basic_do_promote;
  up_args->promotion_closure.cb_arg = up_args;
  grpc_iomgr_add_callback(&up_args->promotion_closure);

  grpc_pollset_kick(pollset, GRPC_POLLSET_KICK_BROADCAST);

exit:
  if (and_unlock_pollset) {
    gpr_mu_unlock(&pollset->mu);
  }
}

static void basic_pollset_del_fd(grpc_pollset *pollset, grpc_fd *fd,
                                 int and_unlock_pollset) {
  GPR_ASSERT(fd);
  if (fd == pollset->data.ptr) {
    GRPC_FD_UNREF(pollset->data.ptr, "basicpoll");
    pollset->data.ptr = NULL;
  }

  if (and_unlock_pollset) {
    gpr_mu_unlock(&pollset->mu);
  }
}

static void basic_pollset_maybe_work(grpc_pollset *pollset,
                                     grpc_pollset_worker *worker,
                                     gpr_timespec deadline, gpr_timespec now,
                                     int allow_synchronous_callback) {
  struct pollfd pfd[2];
  grpc_fd *fd;
  grpc_fd_watcher fd_watcher;
  int timeout;
  int r;
  nfds_t nfds;

  if (pollset->in_flight_cbs) {
    /* Give do_promote priority so we don't starve it out */
    gpr_mu_unlock(&pollset->mu);
    gpr_mu_lock(&pollset->mu);
    return;
  }
  fd = pollset->data.ptr;
  if (fd && grpc_fd_is_orphaned(fd)) {
    GRPC_FD_UNREF(fd, "basicpoll");
    fd = pollset->data.ptr = NULL;
  }
  timeout = grpc_poll_deadline_to_millis_timeout(deadline, now);
  pfd[0].fd = GRPC_WAKEUP_FD_GET_READ_FD(&worker->wakeup_fd);
  pfd[0].events = POLLIN;
  pfd[0].revents = 0;
  nfds = 1;
  if (fd) {
    pfd[1].fd = fd->fd;
    pfd[1].revents = 0;
    gpr_mu_unlock(&pollset->mu);
    pfd[1].events =
        grpc_fd_begin_poll(fd, pollset, POLLIN, POLLOUT, &fd_watcher);
    if (pfd[1].events != 0) {
      nfds++;
    }
  } else {
    gpr_mu_unlock(&pollset->mu);
  }

  /* poll fd count (argument 2) is shortened by one if we have no events
     to poll on - such that it only includes the kicker */
  r = grpc_poll_function(pfd, nfds, timeout);
  GRPC_TIMER_MARK(GRPC_PTAG_POLL_FINISHED, r);

  if (fd) {
    grpc_fd_end_poll(&fd_watcher, pfd[1].revents & POLLIN,
                     pfd[1].revents & POLLOUT);
  }

  if (r < 0) {
    if (errno != EINTR) {
      gpr_log(GPR_ERROR, "poll() failed: %s", strerror(errno));
    }
  } else if (r == 0) {
    /* do nothing */
  } else {
    if (pfd[0].revents & POLLIN) {
      grpc_wakeup_fd_consume_wakeup(&worker->wakeup_fd);
    }
    if (nfds > 1) {
      if (pfd[1].revents & (POLLIN | POLLHUP | POLLERR)) {
        grpc_fd_become_readable(fd, allow_synchronous_callback);
      }
      if (pfd[1].revents & (POLLOUT | POLLHUP | POLLERR)) {
        grpc_fd_become_writable(fd, allow_synchronous_callback);
      }
    }
  }

  gpr_mu_lock(&pollset->mu);
}

static void basic_pollset_destroy(grpc_pollset *pollset) {
  if (pollset->data.ptr != NULL) {
    GRPC_FD_UNREF(pollset->data.ptr, "basicpoll");
    pollset->data.ptr = NULL;
  }
}

static const grpc_pollset_vtable basic_pollset = {
    basic_pollset_add_fd, basic_pollset_del_fd, basic_pollset_maybe_work,
    basic_pollset_destroy, basic_pollset_destroy};

static void become_basic_pollset(grpc_pollset *pollset, grpc_fd *fd_or_null) {
  pollset->vtable = &basic_pollset;
  pollset->data.ptr = fd_or_null;
  if (fd_or_null != NULL) {
    GRPC_FD_REF(fd_or_null, "basicpoll");
  }
}

#endif /* GPR_POSIX_POLLSET */