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// 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
// 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.
#pragma once
#include "FreeRTOS.h"
#include "pw_assert/assert.h"
#include "pw_chrono/system_clock.h"
#include "pw_chrono_freertos/system_clock_constants.h"
#include "pw_interrupt/context.h"
#include "pw_sync/binary_semaphore.h"
#include "semphr.h"
namespace pw::sync {
inline BinarySemaphore::BinarySemaphore() : native_type_() {
const SemaphoreHandle_t handle = xSemaphoreCreateBinaryStatic(&native_type_);
// This should never fail since the pointer provided was not null and it
// should return a pointer to the StaticSemaphore_t.
PW_DASSERT(handle == reinterpret_cast<SemaphoreHandle_t>(&native_type_));
inline BinarySemaphore::~BinarySemaphore() { vSemaphoreDelete(&native_type_); }
inline void BinarySemaphore::release() {
if (interrupt::InInterruptContext()) {
BaseType_t woke_higher_task = pdFALSE;
// It's perfectly fine if the semaphore already has a count of 1.
[[maybe_unused]] BaseType_t already_full = xSemaphoreGiveFromISR(
reinterpret_cast<SemaphoreHandle_t>(&native_type_), &woke_higher_task);
} else { // Task context
// It's perfectly fine if the semaphore already has a count of 1.
[[maybe_unused]] BaseType_t already_full =
inline void BinarySemaphore::acquire() {
// Enforce the pw::sync::BinarySemaphore IRQ contract.
#if INCLUDE_vTaskSuspend == 1 // This means portMAX_DELAY is indefinite.
const BaseType_t result = xSemaphoreTake(
reinterpret_cast<SemaphoreHandle_t>(&native_type_), portMAX_DELAY);
PW_DASSERT(result == pdTRUE);
// In case we need to block for longer than the FreeRTOS delay can represent
// repeatedly hit take until success.
while (xSemaphoreTake(reinterpret_cast<SemaphoreHandle_t>(&native_type_),
chrono::freertos::kMaxTimeout.count()) == pdFALSE) {
#endif // INCLUDE_vTaskSuspend
inline bool BinarySemaphore::try_acquire() noexcept {
if (interrupt::InInterruptContext()) {
BaseType_t woke_higher_task = pdFALSE;
const bool success = xSemaphoreTakeFromISR(
&woke_higher_task) == pdTRUE;
return success;
// Task Context
return xSemaphoreTake(reinterpret_cast<SemaphoreHandle_t>(&native_type_),
0) == pdTRUE;
inline bool BinarySemaphore::try_acquire_until(
chrono::SystemClock::time_point deadline) {
// Note that if this deadline is in the future, it will get rounded up by
// one whole tick due to how try_acquire_for is implemented.
return try_acquire_for(deadline - chrono::SystemClock::now());
inline BinarySemaphore::native_handle_type BinarySemaphore::native_handle() {
return native_type_;
} // namespace pw::sync