/** repeated weakCompareAndSet succeeds in changing value when equal to expected */
public void testWeakCompareAndSet() {
AtomicInteger ai = new AtomicInteger(1);
do {} while (!ai.weakCompareAndSet(1, 2));
do {} while (!ai.weakCompareAndSet(2, -4));
assertEquals(-4, ai.get());
do {} while (!ai.weakCompareAndSet(-4, 7));
assertEquals(7, ai.get());
}
/** 1. 如果当前值 == 预期值，则以原子方式将该设置为给定的更新值。 2. 可能意外失败并且不提供排序保证，所以只有在很少的情况下才对 compareAndSet 进行适当地选择。 */
public void testWeakCompareAndSet() {
AtomicInteger ai = new AtomicInteger();
int expect = 0;
int update = 0;
do {
expect = ai.get();
update = expect + 10;
} while (!ai.weakCompareAndSet(expect, update));
System.out.println(ai.get());
}
private void perf2(AtomicInteger count) {
long startMillis = System.currentTimeMillis();
count.set(0);
for (int i = 0; i < 1000 * 1000 * 100; ++i) {
int value = count.get();
count.weakCompareAndSet(value, value + 1);
}
long millis = System.currentTimeMillis() - startMillis;
System.out.println("weak millis " + millis);
}
/**
* Atomically set this reduction variable to the given updated value if the current value equals
* the expected value. May fail spuriously.
*
* @param expect Expected value.
* @param update Updated value.
* @return True if the update happened, false otherwise.
*/
public boolean weakCompareAndSet(int expect, int update) {
return myValue.weakCompareAndSet(expect, update);
}