=?0???false?:????????addIfAbsent(e,?snapshot);}private?static?int?indexOf(Object?o,?Object[]?elements,???????????????????????????int?index,?int?fence)?{????if?(o?==?null)?{????????for?(int?i?=?index;?i?=?0)????????????????????return?false;????????}????????Object[]?newElements?=?Arrays.copyOf(current,?len?+?1);????????newElements[len]?=?e;????????setArray(newElements);????????return?true;????}?finally?{????????lock.unlock();????}}從源碼可以看出，CopyOnWriteArraySet底層采用了CopyOnWriteArrayList數(shù)據(jù)結(jié)構(gòu)來(lái)實(shí)現(xiàn)。在add元素時(shí)，采用的是可重入鎖來(lái)實(shí)現(xiàn)線程安全。" data-itemshowtype="0" tab="innerlink" data-linktype="2" hasload="1" wah-hotarea="click" style="outline: 0px; -webkit-tap-highlight-color: rgba(0, 0, 0, 0); cursor: pointer;">public?static?void?main(String[]?args)?{
????Set?set?=?new?CopyOnWriteArraySet<>();
????ExecutorService?service?=?Executors.newFixedThreadPool(12);
????int?times?=?10000;
????AtomicInteger?flag?=?new?AtomicInteger(0);
????for(int?i?=?0;?i?times;?i?++){
????????service.execute(()->{
????????????set.add("a"?+?flag.getAndAdd(1));
????????});
????}
????service.shutdown();
????try?{
????????service.awaitTermination(Long.MAX_VALUE,?TimeUnit.DAYS);
????}catch?(Exception?e){
????????e.printStackTrace();
????}
????System.out.println(set.size());
}

=?0???false?:????????addIfAbsent(e,?snapshot);}private?static?int?indexOf(Object?o,?Object[]?elements,???????????????????????????int?index,?int?fence)?{????if?(o?==?null)?{????????for?(int?i?=?index;?i?=?0)????????????????????return?false;????????}????????Object[]?newElements?=?Arrays.copyOf(current,?len?+?1);????????newElements[len]?=?e;????????setArray(newElements);????????return?true;????}?finally?{????????lock.unlock();????}}從源碼可以看出，CopyOnWriteArraySet底層采用了CopyOnWriteArrayList數(shù)據(jù)結(jié)構(gòu)來(lái)實(shí)現(xiàn)。在add元素時(shí)，采用的是可重入鎖來(lái)實(shí)現(xiàn)線程安全。" data-itemshowtype="0" tab="innerlink" data-linktype="2" wah-hotarea="click" hasload="1" style="outline: 0px; -webkit-tap-highlight-color: rgba(0, 0, 0, 0); cursor: pointer;">public?boolean?add(E?e)?{
????return?al.addIfAbsent(e);
}
public?boolean?addIfAbsent(E?e)?{
????Object[]?snapshot?=?getArray();
????return?indexOf(e,?snapshot,?0,?snapshot.length)?>=?0???false?:
????????addIfAbsent(e,?snapshot);
}
private?static?int?indexOf(Object?o,?Object[]?elements,
???????????????????????????int?index,?int?fence)?{
????if?(o?==?null)?{
????????for?(int?i?=?index;?i?????????????if?(elements[i]?==?null)
????????????????return?i;
????}?else?{
????????for?(int?i?=?index;?i?????????????if?(o.equals(elements[i]))
????????????????return?i;
????}
????return?-1;
}
private?boolean?addIfAbsent(E?e,?Object[]?snapshot)?{
????final?ReentrantLock?lock?=?this.lock;
????lock.lock();
????try?{
????????Object[]?current?=?getArray();
????????int?len?=?current.length;
????????if?(snapshot?!=?current)?{
????????????//?Optimize?for?lost?race?to?another?addXXX?operation
????????????int?common?=?Math.min(snapshot.length,?len);
????????????for?(int?i?=?0;?i?????????????????if?(current[i]?!=?snapshot[i]?&&?eq(e,?current[i]))
????????????????????return?false;
????????????if?(indexOf(e,?current,?common,?len)?>=?0)
????????????????????return?false;
????????}
????????Object[]?newElements?=?Arrays.copyOf(current,?len?+?1);
????????newElements[len]?=?e;
????????setArray(newElements);
????????return?true;
????}?finally?{
????????lock.unlock();
????}
}

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