[英]IllegalMonitorException using Semaphore and Monitor in Java
[英]Monitor program using semaphore does not work as expected in java
我試圖在java中創建一個多生產者多個消費者問題的解決方案(即監視器)。
我決定使用Semaphore類並進行如下同步。
import java.util.concurrent.Semaphore;
public class PC implements Runnable {
Semaphore s;
Object lock;
boolean isProducer;
final int ProcessCount = 4;
final int producerDelay = 1500;
final int consumerDelay = 1000;
public static void main(String[] args) {
new PC();
}
PC() {
this.s = new Semaphore(10);
this.lock = new Object();
this.isProducer = true;
// create few consumers and producers
for (int i = 0; i < ProcessCount; i++) {
new Thread(this).start();
}
}
public void run() { //alternately create producers and consumers
if (isProducer) {
isProducer = false;
producer();
} else {
isProducer = true;
consumer();
}
}
void producer() {
try {
while (true) {
synchronized (this.lock) {
s.release(); // produce an resource
}
System.out.println("produced:\tAvailable now:\t" + s.availablePermits());
Thread.sleep(producerDelay);
}
} catch (Exception ex) {
ex.printStackTrace();
}
}
void consumer() {
try {
while (true) {
synchronized (this.lock) {
s.acquire(); // consume resource
}
System.out.println("consumed:\tAvailable now:\t" + s.availablePermits());
Thread.sleep(consumerDelay);
}
} catch (Exception ex) {
ex.printStackTrace();
}
}
}
但輸出並不像預期的那樣。 當生產者延遲小於消費者延遲時,信號量可用資源的數量超過10.另一方面,當生產者延遲更大時,當資源變為0時,程序似乎陷入死鎖(而我希望消費者線程暫停,直到資源線程產生一些東西)
示例輸出:
當消費者延遲較低時:
consumed: Available now: 10
consumed: Available now: 10
produced: Available now: 11
produced: Available now: 10
consumed: Available now: 8
consumed: Available now: 8
produced: Available now: 10
produced: Available now: 10
consumed: Available now: 9
consumed: Available now: 8
produced: Available now: 9
consumed: Available now: 8
produced: Available now: 9
consumed: Available now: 8
consumed: Available now: 7
consumed: Available now: 6
produced: Available now: 7
produced: Available now: 8
consumed: Available now: 7
consumed: Available now: 6
produced: Available now: 7
produced: Available now: 8
consumed: Available now: 7
consumed: Available now: 6
consumed: Available now: 5
consumed: Available now: 4
produced: Available now: 5
produced: Available now: 6
consumed: Available now: 5
consumed: Available now: 4
produced: Available now: 5
produced: Available now: 6
consumed: Available now: 5
consumed: Available now: 4
consumed: Available now: 3
consumed: Available now: 2
produced: Available now: 3
produced: Available now: 4
consumed: Available now: 3
consumed: Available now: 2
produced: Available now: 3
produced: Available now: 4
consumed: Available now: 3
consumed: Available now: 2
consumed: Available now: 0
consumed: Available now: 0
produced: Available now: 2
produced: Available now: 2
consumed: Available now: 1
consumed: Available now: 0
produced: Available now: 1
produced: Available now: 2
consumed: Available now: 1
consumed: Available now: 0
當生產者延遲較低時:
produced: Available now: 11
consumed: Available now: 10
produced: Available now: 11
consumed: Available now: 10
produced: Available now: 11
produced: Available now: 12
consumed: Available now: 11
consumed: Available now: 10
produced: Available now: 11
produced: Available now: 12
produced: Available now: 13
produced: Available now: 12
consumed: Available now: 12
consumed: Available now: 11
produced: Available now: 13
produced: Available now: 14
consumed: Available now: 13
consumed: Available now: 12
produced: Available now: 13
produced: Available now: 14
produced: Available now: 15
produced: Available now: 16
consumed: Available now: 15
consumed: Available now: 14
produced: Available now: 15
produced: Available now: 16
consumed: Available now: 15
consumed: Available now: 14
produced: Available now: 15
produced: Available now: 16
produced: Available now: 17
consumed: Available now: 16
consumed: Available now: 17
produced: Available now: 18
produced: Available now: 17
produced: Available now: 18
consumed: Available now: 17
consumed: Available now: 16
produced: Available now: 17
produced: Available now: 18
consumed: Available now: 16
consumed: Available now: 17
produced: Available now: 17
produced: Available now: 18
produced: Available now: 19
produced: Available now: 20
consumed: Available now: 19
consumed: Available now: 18
produced: Available now: 19
produced: Available now: 20
consumed: Available now: 18
produced: Available now: 19
consumed: Available now: 18
produced: Available now: 20
produced: Available now: 21
produced: Available now: 22
consumed: Available now: 21
consumed: Available now: 20
produced: Available now: 21
produced: Available now: 22
consumed: Available now: 21
consumed: Available now: 20
produced: Available now: 21
produced: Available now: 22
produced: Available now: 23
produced: Available now: 24
consumed: Available now: 23
consumed: Available now: 22
produced: Available now: 23
produced: Available now: 24
程序有什么問題?
首先,創建一個信號量與10個初始許可,如解釋在這里 。 它不是上限,因此release()
可以使可用許可數超過10。
另外,請看下面的代碼:
synchronized (this.lock) {
s.acquire(); // consume resource
}
你獲得了鎖。 如果沒有可用資源,則線程暫停,但不釋放鎖。 因此,下面的代碼無法獲取鎖並且無法執行。 消費者等待許可證,生產者等待鎖定,導致死鎖。
synchronized (this.lock) {
s.release(); // produce an resource
}
您可以通過不同步s.acquire()
和s.release()
來解決此問題。
這就是將要發生的事情
void producer() {
try {
while (true) {
//***All producers are stuck here because "first consumer" is having the lock.
synchronized (this.lock) {
s.release(); // produce an resource
}
System.out.println("produced:\tAvailable now:\t" + s.availablePermits());
Thread.sleep(producerDelay);
}
} catch (Exception ex) {
ex.printStackTrace();
}
}
void consumer() {
try {
while (true) {
//***All other consumers are stuck here because of line below.
synchronized (this.lock) {
//***"First consumer" is stuck here waiting s.release()
s.acquire(); // consume resource
}
System.out.println("consumed:\tAvailable now:\t" + s.availablePermits());
Thread.sleep(consumerDelay);
}
} catch (Exception ex) {
ex.printStackTrace();
}
}
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.