Needed a possibility to notify a thread about event occurred in anothre thread. Originally other attemps were made to organize the necessary approach inside that threads but then idea came up to use a separate object for this kind of synchronization and it finally came out as pretty intelegent light easy to read approach so good that I wanted to share it with you.
/**
* Event Waiter object is to synchronize one or several threads with a thread-event originator</br>
* Thread safe.</br>
* Actors: event originator thread and one or more event waiter thread(s)</br>
* Event Waiter thread(s) must call {@link #waitForEvent()} to wait for the Event to occur</br>
* Event Originator thread must call {@link #eventOccurred()} to notify that the Event has been occurred</br>
* If the Event has been occurred waiter thread(s) are not blocked on {@link #waitForEvent()} call</br>
* If the Event has not been occurred yet waiter thread(s) are blocked on {@link #waitForEvent()} call until the Event has occurred</br>
*
* @author vtkachenko
*
*/
public class EventWaiter {
private boolean eventOccurred = false;
/**
* Once the event has been occurred this method should be called to notify that
*/
public synchronized void eventOccurred() {
eventOccurred = true;
notifyAll();
}
/**
* Method to wait for the event to occur
* @throws InterruptedException
*/
public synchronized void waitForEvent() throws InterruptedException {
if (!eventOccurred) {
wait();
}
}
}
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And usage example.
public class EventWaiterTest {
private static void waitedFirstTest() {
System.out.println("waitedFirstTest begin");
final EventWaiter eventWaiter = new EventWaiter();
Thread threadWithEvent = new Thread(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("occurring the event...");
eventWaiter.eventOccurred();
}
});
threadWithEvent.start();
try {
System.out.println("waiting for the event...");
eventWaiter.waitForEvent();
System.out.println("event occurred");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("waitedFirstTest end");
}
private static void waitedLastTest() {
System.out.println("waitedLastTest begin");
final EventWaiter eventWaiter = new EventWaiter();
Thread threadWithEvent = new Thread(new Runnable() {
@Override
public void run() {
System.out.println("occurring the event...");
eventWaiter.eventOccurred();
}
});
threadWithEvent.start();
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
try {
System.out.println("waiting for the event...");
eventWaiter.waitForEvent();
System.out.println("event occurred");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("waitedLastTest end");
}
/**
* @param args
*/
public static void main(String[] args) {
waitedFirstTest();
waitedLastTest();
}
}
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