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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 <stddef.h>
#include "pw_chrono/system_clock.h"
#include "pw_preprocessor/util.h"
#ifdef __cplusplus
#include "pw_sync_backend/binary_semaphore_native.h"
namespace pw::sync {
// BinarySemaphore is a specialization of CountingSemaphore with arbitrary
// token limit of 1. Note that that max() is >= 1, meaning it may be
// released up to max() times but only acquired once for those N releases.
// Implementations of BinarySemaphore are typically more efficient than the
// default implementation of CountingSemaphore. The entire API is thread safe
// but only a subset is IRQ safe.
// WARNING: In order to support global statically constructed BinarySemaphores,
// the backend MUST ensure that any initialization required in your environment
// prior to the creation and/or initialization of the native semaphore
// (e.g. kernel initialization), is done before or during the invocation of the
// global static C++ constructors.
class BinarySemaphore {
using native_handle_type = backend::NativeBinarySemaphoreHandle;
BinarySemaphore(const BinarySemaphore&) = delete;
BinarySemaphore(BinarySemaphore&&) = delete;
BinarySemaphore& operator=(const BinarySemaphore&) = delete;
BinarySemaphore& operator=(BinarySemaphore&&) = delete;
// Atomically increments the internal counter by 1 up to max_count.
// Any thread(s) waiting for the counter to be greater than 0,
// such as due to being blocked in acquire, will subsequently be unblocked.
// This is IRQ safe.
// 1 <= max() - counter
void release();
// Decrements the internal counter to 0 or blocks indefinitely until it can.
// This is thread safe.
// update <= max() - counter
void acquire();
// Attempts to decrement by the internal counter to 0 without blocking.
// Returns true if the internal counter was reset successfully.
// This is IRQ safe.
bool try_acquire() noexcept;
// Attempts to decrement the internal counter to 0 where, if needed, blocking
// for at least the specified duration.
// Returns true if the internal counter was decremented successfully.
// This is thread safe.
bool try_acquire_for(chrono::SystemClock::duration for_at_least);
// Attempts to decrement the internal counter to 0 where, if needed, blocking
// until at least the specified time point.
// Returns true if the internal counter was decremented successfully.
// This is thread safe.
bool try_acquire_until(chrono::SystemClock::time_point until_at_least);
static constexpr ptrdiff_t max() noexcept {
return backend::kBinarySemaphoreMaxValue;
native_handle_type native_handle();
// This may be a wrapper around a native type with additional members.
backend::NativeBinarySemaphore native_type_;
} // namespace pw::sync
#include "pw_sync_backend/binary_semaphore_inline.h"
using pw_sync_BinarySemaphore = pw::sync::BinarySemaphore;
#else // !defined(__cplusplus)
typedef struct pw_sync_BinarySemaphore pw_sync_BinarySemaphore;
#endif // __cplusplus
void pw_sync_BinarySemaphore_Release(pw_sync_BinarySemaphore* semaphore);
void pw_sync_BinarySemaphore_Acquire(pw_sync_BinarySemaphore* semaphore);
bool pw_sync_BinarySemaphore_TryAcquire(pw_sync_BinarySemaphore* semaphore);
bool pw_sync_BinarySemaphore_TryAcquireFor(
pw_sync_BinarySemaphore* semaphore,
pw_chrono_SystemClock_TickCount for_at_least);
bool pw_sync_BinarySemaphore_TryAcquireUntil(
pw_sync_BinarySemaphore* semaphore,
pw_chrono_SystemClock_TimePoint until_at_least);
ptrdiff_t pw_sync_BinarySemaphore_Max(void);