pw_sync_stl/counting_semaphore.cc

// Copyright 2020 The Pigweed Authors
//
// 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
//
//     https://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 "pw_sync/counting_semaphore.h"

#include "pw_assert/assert.h"

using pw::chrono::SystemClock;

namespace pw::sync {

void CountingSemaphore::release(ptrdiff_t update) {
  PW_DCHECK_UINT_GE(update, 0);
  {
    std::lock_guard lock(native_type_.mutex);
    PW_DCHECK_UINT_LE(update, CountingSemaphore::max() - native_type_.count);
    native_type_.count += update;
    native_type_.condition.notify_one();
  }
}

void CountingSemaphore::acquire() {
  std::unique_lock lock(native_type_.mutex);
  native_type_.condition.wait(lock, [&] { return native_type_.count != 0; });
  --native_type_.count;
}

bool CountingSemaphore::try_acquire() noexcept {
  std::lock_guard lock(native_type_.mutex);
  if (native_type_.count != 0) {
    --native_type_.count;
    return true;
  }
  return false;
}

bool CountingSemaphore::try_acquire_until(
    SystemClock::time_point until_at_least) {
  std::unique_lock lock(native_type_.mutex);
  if (native_type_.condition.wait_until(
          lock, until_at_least, [&] { return native_type_.count != 0; })) {
    --native_type_.count;
    return true;
  }
  return false;
}

}  // namespace pw::sync