java線程中含有waiting與blocked兩種狀態(tài)，兩種狀態(tài)有著明顯的區(qū)別，本文從jdk源碼中兩種狀態(tài)的設(shè)計角度和狀態(tài)進(jìn)入角度來分析兩者的區(qū)別。

源碼分析

    /*
     * Thread state for a thread blocked waiting for a monitor lock.
     * A thread in the blocked state is waiting for a monitor lock
     * to enter a synchronized block/method or
     * reenter a synchronized block/method after calling
     * {@link Object#wait() Object.wait}.
     */
    BLOCKED,

處于 blocked狀態(tài)的線程等待獲取監(jiān)視器鎖以期進(jìn)入同步代碼塊/方法中。

    /**
     * Thread state for a waiting thread.
     * A thread is in the waiting state due to calling one of the
     * following methods:
     * <ul>
     *   <li>{@link Object#wait() Object.wait} with no timeout</li>
     *   <li>{@link #join() Thread.join} with no timeout</li>
     *   <li>{@link LockSupport#park() LockSupport.park}</li>
     * </ul>
     *
     * <p>A thread in the waiting state is waiting for another thread to
     * perform a particular action.
     *
     * For example, a thread that has called <tt>Object.wait()</tt>
     * on an object is waiting for another thread to call
     * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
     * that object. A thread that has called <tt>Thread.join()</tt>
     * is waiting for a specified thread to terminate.
     */
    WAITING,

文檔介紹了導(dǎo)致線程進(jìn)入Wating狀態(tài)的原因以及如何退出Wating狀態(tài)。

區(qū)別

線程可以通過wait,join,LockSupport.park方式進(jìn)入wating狀態(tài)，進(jìn)入wating狀態(tài)的線程等待喚醒(notify或notifyAll)才有機(jī)會獲取cpu的時間片段來繼續(xù)執(zhí)行。

線程的 blocked狀態(tài)往往是無法進(jìn)入同步方法/代碼塊來完成的。這是因為無法獲取到與同步方法/代碼塊相關(guān)聯(lián)的鎖。

與wating狀態(tài)相關(guān)聯(lián)的是等待隊列，與blocked狀態(tài)相關(guān)的是同步隊列，一個線程由等待隊列遷移到同步隊列時，線程狀態(tài)將會由wating轉(zhuǎn)化為blocked。可以這樣說，blocked狀態(tài)是處于wating狀態(tài)的線程重新煥發(fā)生命力的必由之路。