您好,登錄后才能下訂單哦!
這篇文章主要介紹了Java源碼解析阻塞隊(duì)列ArrayBlockingQueue常用方法的示例分析,具有一定借鑒價(jià)值,感興趣的朋友可以參考下,希望大家閱讀完這篇文章之后大有收獲,下面讓小編帶著大家一起了解一下。
首先看一下ArrayBlockingQueue的成員變量。如下圖。最主要的成員變量是items,它是一個(gè)Object類型的數(shù)組用于保存阻塞隊(duì)列中的元素。其次是takeIndex,putIndex,count,分別表示了從隊(duì)列獲取元素的位置,往隊(duì)列里放元素的位置和隊(duì)列中元素的個(gè)數(shù)。然后是lock,notEmpty和notFull三個(gè)和鎖相關(guān)的成員變量。lock是一個(gè)可重入鎖,而notEmpty和notFull是和lock綁定的2個(gè)Condition。對可重入鎖不是很了解的同學(xué),可以參考這篇文章https://www.jb51.net/article/154207.htm。對可重入鎖的理解,是理解ArrayBlockingQueue的基礎(chǔ)。也可以這么說,理解了可重入鎖,那么在理解ArrayBlockingQueue就很順利了。
/** The queued items **/ final Object[] items; /** items index for next take, poll, peek or remove **/ int takeIndex; /** items index for next put, offer, or add **/ int putIndex; /** Number of elements in the queue **/ int count; /** * Concurrency control uses the classic two-condition algorithm * found in any textbook. **/ /** Main lock guarding all access **/ final ReentrantLock lock; /** Condition for waiting takes **/ private final Condition notEmpty; /** Condition for waiting puts **/ private final Condition notFull; /** * Shared state for currently active iterators, or null if there * are known not to be any. Allows queue operations to update * iterator state. **/ transient Itrs itrs = null;
接下來介紹ArrayBlockingQueue的主要方法。首先是入隊(duì)方法。ArrayBlockingQueue的入隊(duì)方法有好幾個(gè),功能略有差異,下面我們逐一介紹各個(gè)入隊(duì)方法。首先看一下put方法,如下圖。put方法的功能是,往隊(duì)列尾部插入指定元素,如果隊(duì)列已滿,那么就等待可用空間。方法的實(shí)現(xiàn)過程是,首先判斷元素是否非空。然后,進(jìn)行加鎖,加鎖后判斷隊(duì)列是否已滿。如果已滿,則等待不滿條件。當(dāng)被喚醒后,進(jìn)行入隊(duì)操作。入隊(duì)方法中,會(huì)喚醒在notEmpty條件上等待的線程。
/** * Inserts the specified element at the tail of this queue, waiting * for space to become available if the queue is full. * @throws InterruptedException {@inheritDoc} * @throws NullPointerException {@inheritDoc} **/ public void put(E e) throws InterruptedException { checkNotNull(e); final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { while (count == items.length) notFull.await(); enqueue(e); } finally { lock.unlock(); } } /** * Inserts element at current put position, advances, and signals. * Call only when holding lock. **/ private void enqueue(E x) { // assert lock.getHoldCount() == 1; // assert items[putIndex] == null; final Object[] items = this.items; items[putIndex] = x; if (++putIndex == items.length) putIndex = 0; count++; notEmpty.signal(); }
另一個(gè)入隊(duì)方法是offer,代碼如下。這個(gè)方法與add方法的區(qū)別是,offer方法是立刻返回的,它并不像add方法那樣,當(dāng)隊(duì)列滿時(shí)會(huì)一直等待。
/** * Inserts the specified element at the tail of this queue if it is * possible to do so immediately without exceeding the queue's capacity, * returning {@code true} upon success and {@code false} if this queue * is full. This method is generally preferable to method {@link #add}, * which can fail to insert an element only by throwing an exception. * @throws NullPointerException if the specified element is null **/ public boolean offer(E e) { checkNotNull(e); final ReentrantLock lock = this.lock; lock.lock(); try { if (count == items.length) return false; else { enqueue(e); return true; } } finally { lock.unlock(); } }
接下來看一下出隊(duì)方法take,代碼如下。首先對可重入鎖加鎖,然后判斷元素個(gè)數(shù)是否為0.如果為0,則等待不空條件,否則進(jìn)行出隊(duì)操作。
public E take() throws InterruptedException { final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { while (count == 0) notEmpty.await(); return dequeue(); } finally { lock.unlock(); } }
ArrayListBlockingqueue中還有其他相關(guān)方法,這里就不一一介紹了。
感謝你能夠認(rèn)真閱讀完這篇文章,希望小編分享的“Java源碼解析阻塞隊(duì)列ArrayBlockingQueue常用方法的示例分析”這篇文章對大家有幫助,同時(shí)也希望大家多多支持億速云,關(guān)注億速云行業(yè)資訊頻道,更多相關(guān)知識等著你來學(xué)習(xí)!
免責(zé)聲明:本站發(fā)布的內(nèi)容(圖片、視頻和文字)以原創(chuàng)、轉(zhuǎn)載和分享為主,文章觀點(diǎn)不代表本網(wǎng)站立場,如果涉及侵權(quán)請聯(lián)系站長郵箱:is@yisu.com進(jìn)行舉報(bào),并提供相關(guān)證據(jù),一經(jīng)查實(shí),將立刻刪除涉嫌侵權(quán)內(nèi)容。