public class Signaling extends Object {
private BooleanLock readyLock;
public Signaling(BooleanLock readyLock) {
this.readyLock = readyLock;
Runnable r = new Runnable() {
public void run() {
try {
runWork();
} catch (Exception x) {
// in case ANY exception slips through
x.printStackTrace();
}
}
};
Thread internalThread = new Thread(r, "internal");
internalThread.start();
}
private void runWork() {
try {
print("about to wait for readyLock to be true");
readyLock.waitUntilTrue(0); // 0 - wait forever
print("readyLock is now true");
} catch (InterruptedException x) {
print("interrupted while waiting for readyLock " + "to become true");
}
}
private static void print(String msg) {
String name = Thread.currentThread().getName();
System.err.println(name + ": " + msg);
}
public static void main(String[] args) {
try {
print("creating BooleanLock instance");
BooleanLock ready = new BooleanLock(false);
print("creating Signaling instance");
new Signaling(ready);
print("about to sleep for 3 seconds");
Thread.sleep(3000);
print("about to setValue to true");
ready.setValue(true);
print("ready.isTrue()=" + ready.isTrue());
} catch (InterruptedException x) {
x.printStackTrace();
}
}
}
class BooleanLock extends Object {
private boolean value;
public BooleanLock(boolean initialValue) {
value = initialValue;
}
public BooleanLock() {
this(false);
}
public synchronized void setValue(boolean newValue) {
if (newValue != value) {
value = newValue;
notifyAll();
}
}
public synchronized boolean waitToSetTrue(long msTimeout)
throws InterruptedException {
boolean success = waitUntilFalse(msTimeout);
if (success) {
setValue(true);
}
return success;
}
public synchronized boolean waitToSetFalse(long msTimeout)
throws InterruptedException {
boolean success = waitUntilTrue(msTimeout);
if (success) {
setValue(false);
}
return success;
}
public synchronized boolean isTrue() {
return value;
}
public synchronized boolean isFalse() {
return !value;
}
public synchronized boolean waitUntilTrue(long msTimeout)
throws InterruptedException {
return waitUntilStateIs(true, msTimeout);
}
public synchronized boolean waitUntilFalse(long msTimeout)
throws InterruptedException {
return waitUntilStateIs(false, msTimeout);
}
public synchronized boolean waitUntilStateIs(boolean state, long msTimeout)
throws InterruptedException {
if (msTimeout == 0L) {
while (value != state) {
wait(); // wait indefinitely until notified
}
// condition has finally been met
return true;
}
// only wait for the specified amount of time
long endTime = System.currentTimeMillis() + msTimeout;
long msRemaining = msTimeout;
while ((value != state) && (msRemaining > 0L)) {
wait(msRemaining);
msRemaining = endTime - System.currentTimeMillis();
}
// May have timed out, or may have met value,
// calculate return value.
return (value == state);
}
}
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