我从 here 得到了例子.但是他们只是一个一个地实现了那个例子。意味着第一个整数产生然后混淆和程序停止。
这是原始示例:
class ProducerConsumerImpl {
// producer consumer problem data
private static final int CAPACITY = 10;
private final Queue queue = new LinkedList<>();
private final Random theRandom = new Random();
// lock and condition variables
private final Lock aLock = new ReentrantLock();
private final Condition bufferNotFull = aLock.newCondition();
private final Condition bufferNotEmpty = aLock.newCondition();
public void put() throws InterruptedException {
aLock.lock();
try {
while (queue.size() == CAPACITY) {
System.out.println(Thread.currentThread().getName()
+ " : Buffer is full, waiting");
bufferNotEmpty.await();
}
int number = theRandom.nextInt();
boolean isAdded = queue.offer(number);
if (isAdded) {
System.out.printf("%s added %d into queue %n", Thread
.currentThread().getName(), number);
// signal consumer thread that, buffer has element now
System.out.println(Thread.currentThread().getName()
+ " : Signalling that buffer is no more empty now");
bufferNotFull.signalAll();
}
} finally {
aLock.unlock();
}
}
public void get() throws InterruptedException {
aLock.lock();
try {
while (queue.size() == 0) {
System.out.println(Thread.currentThread().getName()
+ " : Buffer is empty, waiting");
bufferNotFull.await();
}
Integer value = queue.poll();
if (value != null) {
System.out.printf("%s consumed %d from queue %n", Thread
.currentThread().getName(), value);
// signal producer thread that, buffer may be empty now
System.out.println(Thread.currentThread().getName()
+ " : Signalling that buffer may be empty now");
bufferNotEmpty.signalAll();
}
} finally {
aLock.unlock();
}
}
}
之后我修改了代码并让它像这样工作， 前 10 个 Produce，然后 10 个 Consume，循环运行直到程序终止。 这是我修改后的代码:
class ProducerConsumerImpl {
// producer consumer problem data
private static final int CAPACITY = 10;
private final Queue<Integer> queue = new LinkedList<>();
private final Random theRandom = new Random();
// lock and condition variables
private final Lock aLock = new ReentrantLock();
private final Condition bufferNotFull = aLock.newCondition();
private final Condition bufferNotEmpty = aLock.newCondition();
public void put() throws InterruptedException {
aLock.lock();
try {
while(true){
while (queue.size() == CAPACITY) {
System.out.println(Thread.currentThread().getName()
+ " : Buffer is full, waiting");
bufferNotEmpty.await();
}
int number = theRandom.nextInt();
boolean isAdded = queue.offer(number);
if (isAdded) {
System.out.printf("%s added %d into queue %n", Thread
.currentThread().getName(), number);
}
bufferNotFull.signalAll();
}
} finally {
aLock.unlock();
}
}
public void get() throws InterruptedException {
aLock.lock();
try {
while(true){
while (queue.size() == 0) {
System.out.println(Thread.currentThread().getName()
+ " : Buffer is empty, waiting");
bufferNotFull.await();
}
Integer value = (Integer)queue.poll();
if (value != null) {
System.out.printf("%s consumed %d from queue %n", Thread
.currentThread().getName(), value);
}
bufferNotEmpty.signalAll();
}
} finally {
aLock.unlock();
}
}
}
修改后它工作正常，生成 10 个随机整数，然后一次又一次地消耗这些整数，直到程序存在/终止。但是因为我不是并发方面的大师/专家。
所以我想问一下我修改的代码有没有问题？
我觉得我的 bufferNotFull.signalAll(); 和 bufferNotEmpty.signalAll(); 放置有问题，因为它每次都会通知等待线程。
如果有问题我该如何解决？或者，如果一切正常，请清除我的 bufferNotFull.signalAll();和 bufferNotEmpty.signalAll();放置，因为每次都可以通知等待线程。 混淆。
注意:只是获取和设置代码。(生产和消费)
修改后的代码输出:
PRODUCER added 1062016967 into queue
PRODUCER added 1204607478 into queue
PRODUCER added 1865840177 into queue
PRODUCER added -1279321362 into queue
PRODUCER added -190570442 into queue
PRODUCER added -1344361101 into queue
PRODUCER added 609239106 into queue
PRODUCER added -1480451794 into queue
PRODUCER added 1905208395 into queue
PRODUCER added -420578734 into queue
PRODUCER : Buffer is full, waiting
CONSUMER consumed 1062016967 from queue
CONSUMER consumed 1204607478 from queue
CONSUMER consumed 1865840177 from queue
CONSUMER consumed -1279321362 from queue
CONSUMER consumed -190570442 from queue
CONSUMER consumed -1344361101 from queue
CONSUMER consumed 609239106 from queue
CONSUMER consumed -1480451794 from queue
CONSUMER consumed 1905208395 from queue
CONSUMER consumed -420578734 from queue
CONSUMER : Buffer is empty, waiting
PRODUCER added 1917580670 into queue
so on.........
已编辑
在考虑性能之后，我决定在 signalall(); 语句之前的 put 和 get 方法中添加 if 条件。 (我认为它甚至可以提高性能 0.000000Something)但是中断 await();可能是 deadlock(); 有什么帮助吗？
对于制作人:
if(queue.size() == CAPACITY){
bufferNotFull.signalAll();
}
对于消费者:
if(queue.size() == 0){
bufferNotEmpty.signalAll();
}
最佳答案
修改代码即可。
至于通过在不需要时跳过 .singnalAll() 调用可能的性能优化:仅当条件从 false 更改时发出信号就足够了> 为 true。
对于生产者，您可以使用:
if(isAdded && queue.size() == 1) {
/*
* Element has been *actually added* *into empty queue*
* (previously .size() = 0), thus *queue become non-empty*.
*/
bufferNotFull.signalAll();
}
对于消费者，您可以使用:
if(value && queue.size() == CAPACITY - 1) {
/*
* Element has been *actually consumed* *from full queue*
* (previousely .size() = CAPACITY), thus *queue become non full*.
*/
bufferNotEmpty.signalAll();
}
请注意，这样您就不会消除对服务员不必要的通知(例如，消费者只能等待空队列的元素，因此只有添加第一个元素才会唤醒它)。相反，当明确知道没有线程等待它(例如，消费者不能在非空队列上等待)时，您可以消除对 .notifyAll() 的调用。
关于java - 生产者和消费者在 Java 中使用锁，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/33026063/