文章目錄
- 一、簡介
- 二、源碼分析
- (1)`put(E)`
- (2)`take()`
- 三、應用場景
一、簡介
兩種降低鎖粒度的技術:
- 鎖分解(将一個鎖分解為兩個鎖)
- 鎖分段(把一個鎖分解為多個鎖)
LinkedBlockingQueue
:先進先出,阻塞隊列。擁有
takeLock
和
putLock
兩個鎖。
二、源碼分析
(1) put(E)
put(E)
public void put(E e) throws InterruptedException {
if (e == null) throw new NullPointerException();
int c = -1;
Node<E> node = new Node<E>(e);
final ReentrantLock putLock = this.putLock;
final AtomicInteger count = this.count;
putLock.lockInterruptibly();
try {
// 是否已滿
while (count.get() == capacity) {
// 加入 Condition 隊列,等待
notFull.await();
}
// 入隊
enqueue(node);
// 自增,這裡用 AtomicInteger,是因為有兩個鎖
c = count.getAndIncrement();
// 是否滿
if (c + 1 < capacity)
notFull.signal(); // 喚醒 notFull Condition隊列
} finally {
putLock.unlock();
}
if (c == 0)
signalNotEmpty(); // 鎖 takeLock,喚醒 notEmpty Condition隊列
}
private void signalNotEmpty() {
final ReentrantLock takeLock = this.takeLock;
takeLock.lock();
try {
notEmpty.signal();
} finally {
takeLock.unlock();
}
}
(2) take()
take()
public E take() throws InterruptedException {
E x;
int c = -1;
final AtomicInteger count = this.count;
final ReentrantLock takeLock = this.takeLock;
takeLock.lockInterruptibly();
try {
// 是否有值
while (count.get() == 0) {
notEmpty.await();
}
// 出隊
x = dequeue();
// 自減
c = count.getAndDecrement();
if (c > 1)
notEmpty.signal(); // 喚醒 notEmpty Condition 隊列
} finally {
takeLock.unlock();
}
if (c == capacity)
signalNotFull();
return x;
}
三、應用場景
-
Logger
-
Executors