从不同线程将值添加到全局集中并等待所有线程完成

Question

我是线程新手，想知道是否可以使用线程将大量数据拆分为小任务，从而减少处理时间 我已将 Set 拆分为多个集合列表，并且来自执行程序服务的每个线程占用该集合并将该集合添加到另一个集合（全局声明）abcSet。 我需要每个线程将对象添加到该集合中，并且在所有线程完成添加后，继续使用 abcSet 完成的其余工作 下面是示例代码。请帮忙！！

private static final int PARTITIONS_COUNT = 4;
final Set<Abc> newAbcSet = new HashSet<Abc>();
final Set<Abc> abcSet = //data from database
        ExecutorService e = Executors.newFixedThreadPool(4);
List<Set<Abc>> theSets = new ArrayList<Set<Abc>>(PARTITIONS_COUNT);
// divide set into 4 different sets for threading purpose
for (int i = 0; i < PARTITIONS_COUNT; i++) {
    theSets.add(new HashSet<Abc>());
}

int index = 0;
for (Abc abcObj : abcSet) {
    theSets.get(index++ % PARTITIONS_COUNT).add(abcObj);
}
for (final Set<Abc> abcSet1 : theSets) {
    e.execute(new Runnable() {
        @Override
        public void run() {
            for (Abc abc : abcSet1) {
                //do some modifications with abc and add it to newAbcSet
                newAbcSet.add(abc);
            }

        }
    });

}
//Do something with the newAbcSet

Answer 1

• 为防止种族冲突，您应该使用thread safe Set implemention，例如：

  final Set<Abc> newAbcSet= Collections.synchronizedSet(new HashSet<Abc>());
  

• 如果你不再需要线程池，你可以调用shutdown()和awaitTermination()

  e.shutDown();  //  previously submitted tasks are not affected
  e.awaitTermination();  // Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first.
  
  //Do something with the newAbcSet
  

  如果还需要线程池，请参考question。

Answer 2

在for之后添加while (!e.isTerminated()){}停止执行：

for (final Set<Abc> abcSet1 : theSets) {
    e.execute(new Runnable() {
        @Override
        public void run() {
            for(Abc abc: abcSet1){
                //do some modifications with abc and add it to newAbcSet
                newAbcSet.add(abc);
            }

        }
    });
}

while (!e.isTerminated()){}