Dinesh on Java

Example1: using wait() and sleep():

synchronized(HandObject) {
    while(isHandFree() == false) {
        /* Hand is still busy on happy coding or something else, please wait */
        HandObject.wait();
    }
}

/* Get lock ^^, It is my turn, take a cup beer now */
while (beerIsAvailable() == false) {
    /* Beer is still coming, not available, Hand still hold glass to get beer,
       don't release hand to perform other task */
    Thread.sleep(5000);
}

/* Enjoy my beer now ^^ */
drinkBeers();

/* I have drink enough, now hand can continue with other task: continue coding */
setHandFreeState(true);
HandObject.notifyAll();

Let clarity some key notes:

1. Call on:
   • wait(): Call on current thread that hold HandObject Object
   • sleep(): Call on Thread execute task get beer (is class method so affect on current running thread)
2. Synchronized:
   • wait(): when synchronized multi thread access same Object (HandObject) (When need communication between more than one thread (thread execute coding, thread execute get beer) access on same object HandObject )
   • sleep(): when waiting condition to continue execute (Waiting beer available)
3. Hold lock:
   • wait(): release the lock for other object have chance to execute (HandObject is free, you can do other job)
   • sleep(): keep lock for at least t times (or until interrupt) (My job still not finish, I’m continue hold lock and waiting some condition to continue)
4. Wake-up condition:
   • wait(): until call notify(), notifyAll() from object
   • sleep(): until at least time expire or call interrupt

synchronized(LOCK) {
    Thread.sleep(1000); // LOCK is held
}


synchronized(LOCK) {
    LOCK.wait(); // LOCK is not held
}

It all eventually makes its way down to the OS’s scheduler, which hands out timeslices to processes and threads.

sleep(n) says “I’m done with my timeslice, and please don’t give me another one for at least n milliseconds.” The OS doesn’t even try to schedule the sleeping thread until requested time has passed.

yield() says “I’m done with my timeslice, but I still have work to do.” The OS is free to immediately give the thread another timeslice, or to give some other thread or process the CPU the yielding thread just gave up.

.wait() says “I’m done with my timeslice. Don’t give me another timeslice until someone calls notify().” As with sleep(), the OS won’t even try to schedule your task unless someone calls notify() (or one of a few other wakeup scenarios occurs).

Threads also lose the remainder of their timeslice when they perform blocking IO and under a few other circumstances. If a thread works through the entire timeslice, the OS forcibly takes control roughly as if yield() had been called, so that other processes can run.

You rarely need yield(), but if you have a compute-heavy app with logical task boundaries, inserting a yield() might improve system responsiveness (at the expense of time — context switches, even just to the OS and back, aren’t free). Measure and test against goals you care about, as always.

Difference between yield and sleep in java
Major difference between yield and sleep in Java is that yield() method pauses the currently executing thread temporarily for giving a chance to the remaining waiting threads of the same priority to execute. If there is no waiting thread or all the waiting threads have a lower priority then the same thread will continue its execution. The yielded thread when it will get the chance for execution is decided by the thread scheduler whose behavior is vendor dependent. Yield method doesn’t guarantee that current thread will pause or stop but it guarantee that CPU will be relinquish by current Thread as a result of call to Thread.yield() method in java.