services/inputflinger/SyncQueue.h

/*
 * Copyright 2023 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.
 */

#pragma once

#include <utils/threads.h>
#include <list>
#include <mutex>
#include <optional>

namespace android {

/** A thread-safe FIFO queue. */
template <class T>
class SyncQueue {
public:
    SyncQueue() = default;

    SyncQueue(size_t capacity) : mCapacity(capacity) {}

    /** Retrieve and remove the oldest object. Returns std::nullopt if the queue is empty. */
    std::optional<T> pop() {
        std::scoped_lock lock(mLock);
        if (mQueue.empty()) {
            return {};
        }
        T t = std::move(mQueue.front());
        mQueue.erase(mQueue.begin());
        return t;
    };

    /**
     * Add a new object to the queue.
     * Return true if an element was successfully added.
     * Return false if the queue is full.
     */
    template <class... Args>
    bool push(Args&&... args) {
        std::scoped_lock lock(mLock);
        if (mCapacity && mQueue.size() == mCapacity) {
            return false;
        }
        mQueue.emplace_back(args...);
        return true;
    };

private:
    const std::optional<size_t> mCapacity;
    std::mutex mLock;
    std::list<T> mQueue GUARDED_BY(mLock);
};

} // namespace android