使用线程池运行多个进程的Java runtime.exec（）

Question

In my program I have a list of n test scripts , I need to iterate the list and run 3 test scripts in parallel. To achieve this task I created a Threadpool of size 3. My implementation is like below for the thread pool

ExecutorService executor = Executors.newFixedThreadPool(3);
for (int threadpoolCount = 0; threadpoolCount < classNames.size(); threadpoolCount++) {
    Runnable worker = new ProcessRunnable(classNames.get(threadpoolCount));
    executor.execute(worker);
}
executor.shutdown();
while (!executor.isTerminated()) {
}

System.out.println("Finished all threads");

below is my thread implementation where in i execute a batch file with maven commands in it

public void run() {
    try {
        System.out.println(testname);
        System.out.println("Task ID : " + this.testname + " performed by " + Thread.currentThread().getName());
        Process p = Runtime.getRuntime().exec("cmd /C Junit_runner.bat" + " " + testname);
        p.waitFor();
        Thread.sleep(5000);
    } catch (IOException e) {
        e.printStackTrace();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

Here is what I get in my console (I am not starting the command prompt and running it in background)

com.selenium.test.testname1 Task ID : com.selenium.test.testname1 performed by pool-1-thread-1

com.selenium.test.testname1 Task ID : com.selenium.test.testname2 performed by pool-1-thread-2

com.selenium.test.testname1 Task ID : com.selenium.test.testname3 performed by pool-1-thread-3

The execution pauses here and it didn't do anything , I am not sure what's happening behind. I also cross checked that the batch file its working fine.

Answer 1

The process takes long to execute and so your control is not returning back.

public abstract int waitFor() throws InterruptedException

Causes the current thread to wait, if necessary, until the process represented by this Process object has terminated. This method returns immediately if the subprocess has already terminated. If the subprocess has not yet terminated, the calling thread will be blocked until the subprocess exits.

As waitFor() is a blocking call all the 3 threads are stuck at this line.

NOTE: You don't need Thread.sleep(5000); as waitFor() is itself blocking in nature.

Try executing some other command and see if the control returns.

Also instead of:

while (!executor.isTerminated()) {
}

You can use ExecutorService#awaitTermination()

Answer 2

读取p.getInputStream（）和p.getErrorStream（）并将其而不是thread.sleep（）写入控制台，您将获得线程正在执行的操作的指示。