问题描述
我使用 ForkJoinPool 并行执行任务.当我查看程序的注销时,似乎 ForkJoinPool 创建了大量工作人员来执行我的任务(有如下所示的日志条目:05 Apr 2016 11:39:18,678 [ForkJoinPool-2-worker-2493] <message>
).
I use the ForkJoinPool to execute tasks in parallel. When I look at the logout put of my program it seems that the ForkJoinPool creates a huge amount of workers to execute my tasks (there are log entries that look like this: 05 Apr 2016 11:39:18,678 [ForkJoinPool-2-worker-2493] <message>
).
创建的每个任务是否都有一个工作人员,然后根据我在 ForkJoinPool 中配置的并行数执行,或者我做错了什么?这是我的做法:
Is there a worker for each tasks created which is then executed according to the number of parallelism I configured in the ForkJoinPool or am I doing something wrong? Here is how I do it:
public class MyClass {
private static final int NUM_CORES = Runtime.getRuntime().availableProcessors();
public MyClass() {
int maxThreads = NUM_CORES * 2;
this.forkJoinPool = new ForkJoinPool(maxThreads);
}
public void doStuff() {
final int[] toIndex = {0};
forkJoinPool.submit(() -> {
List<ForkJoinTask> tasks = new ArrayList<>();
while (toIndex[0] < objects.size()) {
toIndex[0] += 20;
List<Object> bucket = objects.subList(toIndex[0] - 20, toIndex[0]);
ForkJoinTask task = new UpdateAction(bucket);
tasks.add(task);
task.fork();
}
tasks.forEach(ForkJoinTask::join);
}).join();
}
private class UpdateAction extends RecursiveAction {
private List<Object> bucket;
private UpdateAction(List<Object> bucket) {
this.bucket = bucket;
}
@Override
protected void compute() {
// do some calculation
}
}
}
推荐答案
任务名称末尾的数字与池实际使用的线程数无关.看一下 ForkJoinPool 类的 registerWorker 方法.它看起来像这样:
The number at the end of a task name has nothing to do with the actual number of threads used by the pool. Take a look at the registerWorker method of the ForkJoinPool class. It looks something like this:
final WorkQueue registerWorker(ForkJoinWorkerThread wt) {
UncaughtExceptionHandler handler;
wt.setDaemon(true); // configure thread
if ((handler = ueh) != null)
wt.setUncaughtExceptionHandler(handler);
WorkQueue w = new WorkQueue(this, wt);
int i = 0; // assign a pool index
int mode = config & MODE_MASK;
int rs = lockRunState();
...
// some manipulations with i counter
...
wt.setName(workerNamePrefix.concat(Integer.toString(i >>> 1)));
return w;
}
workerNamePrefix 被初始化为
"ForkJoinPool-" + nextPoolId() + "-worker-"
如果您想测量池使用的实际线程数,最好记录 getPoolSize() 返回的内容.
If you want to measure the real number of threads used by the pool you better log what getPoolSize() returns.
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