对象池common-pool2源码分析

对象池common-pool2策略分析

从前两篇的分析中可以看出对象池中的对象会被激活,钝化,销毁等,那么做这些操作的对象需要满足什么条件呢,与这些操作之后相对应的对象的状态是什么样的呢?

首先从PooledObjectState开始分析

public enum PooledObjectState {/*** In the queue, not in use.*/IDLE,/*** In use.*/ALLOCATED,/*** In the queue, currently being tested for possible eviction.*/EVICTION,/*** Not in the queue, currently being tested for possible eviction. An* attempt to borrow the object was made while being tested which removed it* from the queue. It should be returned to the head of the queue once* eviction testing completes.* TODO: Consider allocating object and ignoring the result of the eviction*       test.*/EVICTION_RETURN_TO_HEAD,/*** In the queue, currently being validated.*/VALIDATION,/*** Not in queue, currently being validated. The object was borrowed while* being validated and since testOnBorrow was configured, it was removed* from the queue and pre-allocated. It should be allocated once validation* completes.*/VALIDATION_PREALLOCATED,/*** Not in queue, currently being validated. An attempt to borrow the object* was made while previously being tested for eviction which removed it from* the queue. It should be returned to the head of the queue once validation* completes.*/VALIDATION_RETURN_TO_HEAD,/*** Failed maintenance (e.g. eviction test or validation) and will be / has* been destroyed*/INVALID,/*** Deemed abandoned, to be invalidated.*/ABANDONED,/*** Returning to the pool.*/RETURNING
}

以上枚举定义了对象可以出现的所有状态:

IDLE,空闲,在队列中;

ALLOCATED:在使用;

EVICTION:在队列中,正在测试中,可能会被驱逐;

EVICTION_RETURN_TO_HEAD:不是在队列中,正在测试中,可能会被驱逐.当驱逐测试结束的时候,它应该返回队列的前端;

VALIDATION:在队列中,正在校验;

VALIDATION_PREALLOCATED:不在队列中,使用前进行校验;

VALIDATION_RETURN_TO_HEAD:不在队列中,正在校验,校验结束后应该返回队列的前端;

INVALID:无效的;

ABANDONED:废弃的;

RETURNING:还回对象池.

池对象状态的改变发生在使用,还回,激活等操作的时候,即在调用GenericObjectPool内相应的方法时发生改变.

但DefaultPooledObject的方法里能更清晰的看到状态的变化.

对象创建后默认的状态是空闲

private PooledObjectState state = PooledObjectState.IDLE;

开始驱逐前的测试,状态由空闲变为测试中

public synchronized boolean startEvictionTest() {if (state == PooledObjectState.IDLE) {state = PooledObjectState.EVICTION;return true;}return false;
}

测试结束,由测试中变为空闲

public synchronized boolean endEvictionTest(Deque<PooledObject<T>> idleQueue) {if (state == PooledObjectState.EVICTION) {state = PooledObjectState.IDLE;return true;} else if (state == PooledObjectState.EVICTION_RETURN_TO_HEAD) {state = PooledObjectState.IDLE;if (!idleQueue.offerFirst(this)) {// TODO - Should never happen}}return false;
}

由空闲变为在使用,或由在队列中正在进行测试变为不在队列中正在测试

public synchronized boolean allocate() {if (state == PooledObjectState.IDLE) {state = PooledObjectState.ALLOCATED;lastBorrowTime = System.currentTimeMillis();lastUseTime = lastBorrowTime;borrowedCount++;if (logAbandoned) {borrowedBy = new AbandonedObjectCreatedException();}return true;} else if (state == PooledObjectState.EVICTION) {// TODO Allocate anyway and ignore eviction teststate = PooledObjectState.EVICTION_RETURN_TO_HEAD;return false;}// TODO if validating and testOnBorrow == true then pre-allocate for// performancereturn false;
}

由在使用变为归还

public synchronized boolean deallocate() {if (state == PooledObjectState.ALLOCATED ||state == PooledObjectState.RETURNING) {state = PooledObjectState.IDLE;lastReturnTime = System.currentTimeMillis();borrowedBy = null;return true;}return false;
}

无效的

public synchronized void invalidate() {state = PooledObjectState.INVALID;
}