CODEWITHSUNDEEP
javamultithreadingconcurrency
Brijendar Bakchodia
Brijendar Bakchodia

Reputation: 1797

Why is waiting for Condition in a while loop?

From the official Java Documentation of the class Condition

public void put(E x) throws InterruptedException {
    lock.lock();
    try {
        while (count == items.length)
            notFull.await();

        items[putptr] = x;

        if (++putptr == items.length)
            putptr = 0;

        ++count;
        notEmpty.signal();
    } finally {
        lock.unlock();
    }
}

What is the role of having notFull.await() in a while loop? I am not seeing what this does. Can anyone provide a simple explanation?

Upvotes: 1

Views: 287

Answers (2)

Olli
Olli

Reputation: 679

The reason for the while loop is explained in the Condition documentation:

When waiting upon a Condition, a "spurious wakeup" is permitted to occur, in general, as a concession to the underlying platform semantics. This has little practical impact on most application programs as a Condition should always be waited upon in a loop, testing the state predicate that is being waited for. An implementation is free to remove the possibility of spurious wakeups but it is recommended that applications programmers always assume that they can occur and so always wait in a loop.

Upvotes: 2

xingbin
xingbin

Reputation: 28279

Suppose there are two waiting threads. Both get notified. Only one of them should move forward. Another have to re-check and wait.

Upvotes: 1

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