cocos_lib/cocos/core/utils/Pool.h

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#pragma once

/**
 * @en
 * A fixed-length object pool designed for general type.<br>
 * The implementation of this object pool is very simple,
 * it can helps you to improve your game performance for objects which need frequent release and recreate operations<br/>
 * @zh
 * 长度固定的对象缓存池，可以用来缓存各种对象类型。<br/>
 * 这个对象池的实现非常精简，它可以帮助您提高游戏性能，适用于优化对象的反复创建和销毁。
 * @class js.Pool
 * @example
 * ```
 *
 * Example 1:
 *
 * function Details () {
 *     uuidList = [];
 * };
 * Details.prototype.reset = function () {
 *     uuidList.length = 0;
 * };
 * Details.pool = new js.Pool(function (obj) {
 *     obj.reset();
 * }, 5);
 * Details.pool.get = function () {
 *     return _get() || new Details();
 * };
 *
 * var detail = Details.pool.get();
 * ...
 * Details.pool.put(detail);
 *
 * Example 2:
 *
 * function Details (buffer) {
 *    uuidList = buffer;
 * };
 * ...
 * Details.pool.get = function (buffer) {
 *     var cached = _get();
 *     if (cached) {
 *         cached.uuidList = buffer;
 *         return cached;
 *     }
 *     else {
 *         return new Details(buffer);
 *     }
 * };
 *
 * var detail = Details.pool.get( [] );
 * ...
 * ```
 */

#include <functional>
#include <memory>

#include "base/Macros.h"

template <typename T>
class Pool {
public:
    using CleanUpFunction = std::function<bool(T &)>;

    /**
     * @en
     * Get and initialize an object from pool. This method defaults to null and requires the user to implement it.
     * @zh
     * 获取并初始化对象池中的对象。这个方法默认为空，需要用户自己实现。
     * @param args - parameters to used to initialize the object
     */
    std::function<T()> get{};

    /**
     * 使用构造函数来创建一个指定对象类型的对象池，您可以传递一个回调函数，用于处理对象回收时的清理逻辑。
     * @method constructor
     * @param {Function} [cleanupFunc] - the callback method used to process the cleanup logic when the object is recycled.
     * @param {Object} cleanupFunc.obj
     * @param {Number} size - initializes the length of the array
     */
    Pool(const CleanUpFunction &cleanup, int32_t size) {
        _count = 0;
        _pool.resize(size);
        _cleanup = cleanup;
    }

    /**
     * 使用构造函数来创建一个指定对象类型的对象池，您可以传递一个回调函数，用于处理对象回收时的清理逻辑。
     * @method constructor
     * @param {Function} [cleanupFunc] - the callback method used to process the cleanup logic when the object is recycled.
     * @param {Object} cleanupFunc.obj
     * @param {Number} size - initializes the length of the array
     */
    explicit Pool(int32_t size)
    : Pool{nullptr, size} {}

    ~Pool() = default;

    /**
     * @en
     * Get an object from pool, if no available object in the pool, null will be returned.
     * @zh
     * 获取对象池中的对象，如果对象池没有可用对象，则返回空。
     */
    T _get() { //NOLINT(readability-identifier-naming)
        if (_count > 0) {
            --_count;
            T cache = _pool[_count];
            _pool[_count] = nullptr;
            return cache;
        }
        return nullptr;
    }

    /**
     * @en Put an object into the pool.
     * @zh 向对象池返还一个不再需要的对象。
     */
    void put(T &obj) {
        if (_count < static_cast<int32_t>(_pool.size())) {
            if (_cleanup != nullptr && !_cleanup(obj)) {
                return;
            }
            _pool[_count] = obj;
            ++_count;
        }
    }

    /**
     * @en Resize the pool.
     * @zh 设置对象池容量。
     */
    void resize(int32_t length) {
        if (length >= 0) {
            _pool.resize(length);
            if (_count > length) {
                _count = length;
            }
        }
    }

    int32_t getCount() const { return _count; }

private:
    ccstd::vector<T> _pool;
    CleanUpFunction _cleanup{nullptr};

    /**
     * @en
     * The current number of available objects, the default is 0, it will gradually increase with the recycle of the object,
     * the maximum will not exceed the size specified when the constructor is called.
     * @zh
     * 当前可用对象数量，一开始默认是 0，随着对象的回收会逐渐增大，最大不会超过调用构造函数时指定的 size。
     * @default 0
     */
    int32_t _count{0};

    CC_DISALLOW_COPY_MOVE_ASSIGN(Pool);
};