I'm trying to implement a condition that only one thread to access: Let's say it's a bottle of water - I want only 1 person (thread) to be able to have it a time. Everything seems to work smoothly but I can't get the printing to be shown - the one before the call to wait(); .
public synchronized void getBotttle {
while(myCondition) {
try {
System.out.println("Printing that is never done?!");
wait();
}
catch (InterruptedException e) {}
}
System.out.println("Printing that works");
myCondition = true;
notifyAll(); //or notify(), tried both
try {
Thread.sleep(time); //
}
catch (InterruptedException e) {}
System.out.println("Printing again");
methodToMakeConditionFalse();
// notifyAll(); even if I put it here its still the same
}
This method is called by the threads and it works as intended - only 1 thread has the "bottle" but the printing isn't there. Any ideas?
You don't have a complete example, which makes it hard to tell what you're doing wrong; my guess is that your condition flag isn't set appropriately. Here is a complete example which works, it makes sure that only one thread has access to a resource at a time.
public class StuffExample {
public static void main(String[] args) throws Exception {
Worker worker = new Worker(new StuffHolder());
Thread t1 = new Thread(worker);
Thread t2 = new Thread(worker);
t1.start();
t2.start();
Thread.sleep(10000L);
t1.interrupt();
t2.interrupt();
}
}
class Worker implements Runnable {
private StuffHolder holder;
public Worker(StuffHolder holder) {
this.holder = holder;
}
public void run() {
try {
while (!Thread.currentThread().isInterrupted()) {
holder.useStuff();
Thread.sleep(1000L);
}
}
catch (InterruptedException e) {
}
}
}
class StuffHolder {
private boolean inUse = false;
private int count = 0;
public synchronized void useStuff() throws InterruptedException {
while (inUse) {
wait();
}
inUse = true;
System.out.println("doing whatever with stuff now, count="
+ count + ", thread=" + Thread.currentThread().getName());
count += 1;
inUse = false;
notifyAll();
}
}
Output is:
doing whatever with stuff now, count=0, threadid=Thread-0
doing whatever with stuff now, count=1, threadid=Thread-1
doing whatever with stuff now, count=2, threadid=Thread-0
doing whatever with stuff now, count=3, threadid=Thread-1
doing whatever with stuff now, count=4, threadid=Thread-0
doing whatever with stuff now, count=5, threadid=Thread-1
doing whatever with stuff now, count=6, threadid=Thread-0
doing whatever with stuff now, count=7, threadid=Thread-1
doing whatever with stuff now, count=8, threadid=Thread-0
doing whatever with stuff now, count=9, threadid=Thread-1
doing whatever with stuff now, count=10, threadid=Thread-0
doing whatever with stuff now, count=11, threadid=Thread-1
doing whatever with stuff now, count=12, threadid=Thread-0
doing whatever with stuff now, count=13, threadid=Thread-1
doing whatever with stuff now, count=14, threadid=Thread-0
doing whatever with stuff now, count=15, threadid=Thread-1
doing whatever with stuff now, count=16, threadid=Thread-1
doing whatever with stuff now, count=17, threadid=Thread-0
doing whatever with stuff now, count=18, threadid=Thread-1
doing whatever with stuff now, count=19, threadid=Thread-0