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了解JAVA并發(fā)工具常用設(shè)計(jì)套路

更新時(shí)間：2019年06月19日 09:12:23 作者：clawhub

這篇文章主要介紹了了解JAVA并發(fā)工具常用設(shè)計(jì)套路,文中通過(guò)示例代碼介紹的非常詳細(xì)，對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值，,需要的朋友可以參考下

前言

在學(xué)習(xí)JAVA并發(fā)工具時(shí)，分析JUC下的源碼，發(fā)現(xiàn)有三個(gè)利器：狀態(tài)、隊(duì)列、CAS。

狀態(tài)

一般是state屬性，如AQS源碼中的狀態(tài)，是整個(gè)工具的核心，一般操作的執(zhí)行都要看當(dāng)前狀態(tài)是什么，
由于狀態(tài)是多線程共享的，所以都是volatile修飾，保證線程直接內(nèi)存可見(jiàn)。

/**
* AbstractQueuedSynchronizer中的狀態(tài)
*/
private volatile int state;

/**
* Status field, taking on only the values:
* SIGNAL: The successor of this node is (or will soon be)
* blocked (via park), so the current node must
* unpark its successor when it releases or
* cancels. To avoid races, acquire methods must
* first indicate they need a signal,
* then retry the atomic acquire, and then,
* on failure, block.
* CANCELLED: This node is cancelled due to timeout or interrupt.
* Nodes never leave this state. In particular,
* a thread with cancelled node never again blocks.
* CONDITION: This node is currently on a condition queue.
* It will not be used as a sync queue node
* until transferred, at which time the status
* will be set to 0. (Use of this value here has
* nothing to do with the other uses of the
* field, but simplifies mechanics.)
* PROPAGATE: A releaseShared should be propagated to other
* nodes. This is set (for head node only) in
* doReleaseShared to ensure propagation
* continues, even if other operations have
* since intervened.
* 0: None of the above
*
* The values are arranged numerically to simplify use.
* Non-negative values mean that a node doesn't need to
* signal. So, most code doesn't need to check for particular
* values, just for sign.
*
* The field is initialized to 0 for normal sync nodes, and
* CONDITION for condition nodes. It is modified using CAS
* (or when possible, unconditional volatile writes).
*/
volatile int waitStatus;

隊(duì)列

隊(duì)列一般由鏈表實(shí)現(xiàn)（單向鏈表，雙向鏈表），在線程獲取不到想要的資源或者狀態(tài)時(shí)，將線程封裝成特定節(jié)點(diǎn)，扔到等待隊(duì)列中，等待時(shí)機(jī)成熟，再?gòu)年?duì)列中取出，是悲觀鎖思想。
如AQS中的Node節(jié)點(diǎn)，代碼太長(zhǎng)就不貼了。

CAS

CAS操作是樂(lè)觀鎖思想，是輕量級(jí)的并發(fā)處理。一般用于對(duì)上述狀態(tài)的修改，而且能保證有且只有一個(gè)線程能修改這個(gè)狀態(tài)。
一般由Unsafe類中的compareAndSwap之類的方法實(shí)現(xiàn)。使用CAS,往往伴隨自旋，如果修改狀態(tài)失敗，則不斷地重試，直到修改狀態(tài)成功。

以上就是java并發(fā)編程中的套路，抓住這個(gè)思路，想必能在學(xué)習(xí)中有所幫助。

以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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