Illegalmonitorstateexception on wait() call

Taming threads and conquering concurrency

Harnessing concurrency libraries

Forget fumbling with low-level thread synchronization. Java's java.util.concurrent package grants you higher-level structures that ease threading and reduce errors. Consider ReentrantLock and Condition from java.util.concurrent.locks. They untangle lock handling and condition management:

ReentrantLock lock = new ReentrantLock();
Condition condition = lock.newCondition();

lock.lock(); // I've got the power! 💪
try {
    while (!happyHour()) { // Is it beer o'clock yet?
        condition.await();
    }
    // Time to enjoy that well-deserved beer! 🍺 
} finally {
    lock.unlock(); // Sharing is caring! 😌
}
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CountdownLatch: a simple alternative

A CountDownLatch is akin to a countdown timer at a rocket launch. Imagine pausing threads until specific operations are done. It shines when awaiting a fixed number of events:

CountDownLatch latch = new CountDownLatch(1);

// The waiting thread
latch.await(); // Are we there yet?

// Thread that signals completion
latch.countDown(); // Blast off! 🚀
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Evading common blunders

Shun the use of Thread instances as locks. They can introduce unwanted side effects. Instead, use dedicated lock objects or classes designed for locking for hassle-free code.

Wakey-wakey, threads!

Ensure that threads wake up only when necessary by verifying the condition within a while loop:

synchronized (object) {
    while (!coffeeReady()) {
        object.wait(); // Circulate the coffee! ☕ 
    }
    // The coffee is ready! Let's sip!
}
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Clear code, happy devs

Make your threading operations explicit with named classes. Debugging feels like a stroll in the park.

No need to reinvent the wheel

Instead of grueling manual thread safety, why not use concurrent collections like ConcurrentHashMap or CopyOnWriteArrayList? They offer built-in safety from race conditions.