Java中的IllegalMonitorStateException
- java
1.概述
在這個簡短的教程中，我們將學習java.lang.IllegalMonitorStateException.
我們將創建一個簡單的發送方-接收方應用程序，該應用程序將引發此異常。然後，我們將討論防止這種情況的可能方法。最後，我們將展示如何正確實現這些發送者和接收者類。
2.什麼時候拋出此異常？
IllegalMonitorStateException與Java中的多線程編程有關。如果我們有一個monitor ，則拋出此異常，以表明某個線程試圖等待，或者通知其他線程在該監視器上等待而不擁有它。用簡單的話來說，如果我們在synchronized塊Object wait() ， notify(),或notifyAll()方法之一，則會得到此異常。
現在讓我們構建一個拋出IllegalMonitorStateException的示例。為此，我們將同時使用wait()和notifyAll()方法來同步發送方和接收方之間的數據交換。
首先，讓我們看一下保存將要發送的消息Data
public class Data {
private String message;
public void send(String message) {
this.message = message;
}
public String receive() {
return message;
}
}其次，讓我們創建在被調用時IllegalMonitorStateException .為此，我們將調用notifyAll()方法，而不將其包裝在synchronized塊中：
class UnsynchronizedSender implements Runnable {
private static final Logger log = LoggerFactory.getLogger(UnsychronizedSender.class);
private final Data data;
public UnsynchronizedSender(Data data) {
this.data = data;
}
@Override
public void run() {
try {
Thread.sleep(1000);
data.send("test");
data.notifyAll();
} catch (InterruptedException e) {
log.error("thread was interrupted", e);
Thread.currentThread().interrupt();
}
}
}接收者還將引發IllegalMonitorStateException.與前面的示例類似，我們將在synchronized塊wait()
public class UnsynchronizedReceiver implements Runnable {
private static final Logger log = LoggerFactory.getLogger(UnsynchronizedReceiver.class);
private final Data data;
private String message;
public UnsynchronizedReceiver(Data data) {
this.data = data;
}
@Override
public void run() {
try {
data.wait();
this.message = data.receive();
} catch (InterruptedException e) {
log.error("thread was interrupted", e);
Thread.currentThread().interrupt();
}
}
public String getMessage() {
return message;
}
}最後，讓我們實例化這兩個類並在它們之間發送一條消息：
public void sendData() {
Data data = new Data();
UnsynchronizedReceiver receiver = new UnsynchronizedReceiver(data);
Thread receiverThread = new Thread(receiver, "receiver-thread");
receiverThread.start();
UnsynchronizedSender sender = new UnsynchronizedSender(data);
Thread senderThread = new Thread(sender, "sender-thread");
senderThread.start();
senderThread.join(1000);
receiverThread.join(1000);
}當我們嘗試運行這段代碼時，我們將同時從UnsynchronizedReceiver和UnsynchronizedSender類IllegalMonitorStateException
[sender-thread] ERROR 1ju.org.exceptions.illegalmonitorstate.UnsynchronizedSender - illegal monitor state exception occurred
java.lang.IllegalMonitorStateException: null
at java.base/java.lang.Object.notifyAll(Native Method)
at 1ju.org.exceptions.illegalmonitorstate.UnsynchronizedSender.run(UnsynchronizedSender.java:15)
at java.base/java.lang.Thread.run(Thread.java:844)
[receiver-thread] ERROR 1ju.org.exceptions.illegalmonitorstate.UnsynchronizedReceiver - illegal monitor state exception occurred
java.lang.IllegalMonitorStateException: null
at java.base/java.lang.Object.wait(Native Method)
at java.base/java.lang.Object.wait(Object.java:328)
at 1ju.org.exceptions.illegalmonitorstate.UnsynchronizedReceiver.run(UnsynchronizedReceiver.java:12)
at java.base/java.lang.Thread.run(Thread.java:844)3.如何修復
**要擺脫IllegalMonitorStateException,我們需要synchronized塊內進行wait() ， notify(),和notifyAll()**考慮到這一點，讓我們看一下Sender類的正確實現應如何：
class SynchronizedSender implements Runnable {
private final Data data;
public SynchronizedSender(Data data) {
this.data = data;
}
@Override
public void run() {
synchronized (data) {
data.send("test");
data.notifyAll();
}
}
}請注意，我們在Data synchronized塊，我們稍後將其稱為notifyAll()方法。
讓我們以相同的方式Receiver
class SynchronizedReceiver implements Runnable {
private static final Logger log = LoggerFactory.getLogger(SynchronizedReceiver.class);
private final Data data;
private String message;
public SynchronizedReceiver(Data data) {
this.data = data;
}
@Override
public void run() {
synchronized (data) {
try {
data.wait();
this.message = data.receive();
} catch (InterruptedException e) {
log.error("thread was interrupted", e);
Thread.currentThread().interrupt();
}
}
}
public String getMessage() {
return message;
}
}如果我們再次創建兩個類並嘗試在它們之間發送相同的消息，則一切正常，並且不會引發異常。
4 結論
在本文中，我們了解了導致IllegalMonitorStateException原因以及如何防止它。