src/base/event.cc

/*
 * Copyright (C) 2018 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <stdint.h>
#include <unistd.h>

#include "perfetto/base/event.h"
#include "perfetto/base/logging.h"

#if PERFETTO_USE_EVENTFD()
#include <sys/eventfd.h>
#endif

namespace perfetto {
namespace base {

Event::Event() {
#if PERFETTO_USE_EVENTFD()
  fd_.reset(eventfd(/* start value */ 0, EFD_CLOEXEC | EFD_NONBLOCK));
  PERFETTO_CHECK(fd_);
#else
  int pipe_fds[2];
  PERFETTO_CHECK(pipe(pipe_fds) == 0);

  // Make the pipe non-blocking so that we never block the waking thread (either
  // the main thread or another one) when scheduling a wake-up.
  for (auto fd : pipe_fds) {
    int flags = fcntl(fd, F_GETFL, 0);
    PERFETTO_CHECK(flags != -1);
    PERFETTO_CHECK(fcntl(fd, F_SETFL, flags | O_NONBLOCK) == 0);
    PERFETTO_CHECK(fcntl(fd, F_SETFD, FD_CLOEXEC) == 0);
  }
  fd_.reset(pipe_fds[0]);
  write_fd_.reset(pipe_fds[1]);
#endif  // !PERFETTO_USE_EVENTFD()
}

Event::~Event() = default;

void Event::Notify() {
  const uint64_t value = 1;

#if PERFETTO_USE_EVENTFD()
  ssize_t ret = write(fd_.get(), &value, sizeof(value));
#else
  ssize_t ret = write(write_fd_.get(), &value, sizeof(uint8_t));
#endif

  if (ret <= 0 && errno != EAGAIN) {
    PERFETTO_DPLOG("write()");
    PERFETTO_DCHECK(false);
  }
}

void Event::Clear() {
#if PERFETTO_USE_EVENTFD()
  uint64_t value;
  ssize_t ret = read(fd_.get(), &value, sizeof(value));
#else
  // Drain the byte(s) written to the wake-up pipe. We can potentially read
  // more than one byte if several wake-ups have been scheduled.
  char buffer[16];
  ssize_t ret = read(fd_.get(), &buffer[0], sizeof(buffer));
#endif
  if (ret <= 0 && errno != EAGAIN)
    PERFETTO_DPLOG("read()");
}

}  // namespace base
}  // namespace perfetto