java - ExecutorService - 并行运行任务并保存结果

Question

我想同时向最多 10 个用户发送 ping，并在 ping 完成后用结果更新用户对象。

为了做到这一点，我尝试使用 ExecutorService .

我从这样的代码开始:

private void pingUsers(List<User> userList) throws ExecutionException, InterruptedException {
    final int NUM_THREADS = 10;
    ExecutorService executor = Executors.newFixedThreadPool(NUM_THREADS);

    for (User user : userList) {
        SnmpPingDevice pingUser = new PingUser(user);
        Future<Boolean> isUserActive = executor.submit(pingUser);
        user.isActive = isUserActive.get() ; // -- I guess it will block other pings and i'm back to my starting point where I need to run the pings in parallel.
    }

    executor.shutdown();
    try {
        executor.awaitTermination(30, TimeUnit.SECONDS);


    } catch (InterruptedException e) {
        logger.error("Failed to terminate executor");
    }
}

这就是我的 PingUser 类的样子:

@Override
    public Boolean call() {
        ping = new CmdRunner(toolDir,outDir,
                new UserOidWorkerPing(version,community,ip,logger));

        return this.isActive();
    }

public boolean isActive(){
        String cmd = ping.getCmdNoRedirect(); 
        String rc = this.cmdRunner.runShellCmd(cmd,this.outDir +"/dummy",false);
        logger.debug("PING was sent with cmd:" + cmd + ",rc:" + rc);
        return rc != null && !rc.contains("Timeout:") && !rc.isEmpty();
    }

回到同一个问题，ping 不会并行运行(一旦循环等待 isUserActive.get() 结束)

知道我错过了什么吗？我如何使这些 ping 并行运行并将每个用户的结果保存在我的 List<User> userList 中？

Answer 1

Future::get 是一个阻塞操作，因此调用线程将被阻塞，直到调用完成。因此，只有在前一个任务完成后，您才能提交新任务。

考虑使用ExecutorService::invokeAll这将返回一个 Future 列表:

List<PingUser> pingUsers = userList.stream().map(PingUser::new).collect(Collectors.toList());
List<Future<Boolean>> results = executor.invokeAll(pingUsers);