CON31-J. Ensure that tasks submitted to a thread pool are interruptible

According to the Java API interface java.util.concurrent.ExecutorService, method shutdownNow() documentation [[API 06]]:

Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution. There are no guarantees beyond best-effort attempts to stop processing actively executing tasks. For example, typical implementations will cancel via Thread.interrupt(), so any task that fails to respond to interrupts may never terminate.

Consequently, tasks that do not support interruption using Thread.interrupt() should not be submitted to a thread pool. Similarly, when attempting to cancel individual tasks within the thread pool using the Future.cancel() method, ensure that the tasks support interruption.

Noncompliant Code Example (shutting down thread pools)

This noncompliant code example uses the SocketReader class defined earlier in the Compliant Solution (close socket connection) of the guideline CON26-J. Ensure that threads and tasks performing blocking operations can be terminated and submits it as a task to a thread pool defined in class PoolService.

public final class PoolService {
  private final ExecutorService pool;

  public PoolService(int poolSize) {
    pool = Executors.newFixedThreadPool(poolSize);
  }
	  
  public void doSomething() throws InterruptedException, IOException {	   
    pool.submit(new SocketReader());
    // ...
    List<Runnable> awaitingTasks = pool.shutdownNow();	      
  }

  public static void main(String[] args) throws InterruptedException, IOException {
    PoolService service = new PoolService(5);
    service.doSomething();
  }
}

public final class SocketReader implements Runnable {
  private final Socket socket;
  // ...
}

Because the task does not support interruption through the use of Thread.interrupted(), there is no guarantee that the shutdownNow() method will quiickly shutdown the thread pool. Using the shutdown() method does not fix the problem either, because it waits until all executing tasks have finished.

Similarly, tasks that use some mechanism other than Thread.interrupted() to determine when to shutdown will be unresponsive to shutdown() or shutdownNow(). For instance, tasks that check a volatile flag to determine whether it is safe to shutdown will be unresponsive to these methods. The guideline CON24-J. Do not use Thread.stop() to terminate threads provides more information on using a flag to terminate threads.

Compliant Solution (submit interruptible tasks)

This compliant solution submits the interruptible version of SocketReader discussed in the Compliant Solution (interruptible channel) of the guideline CON26-J. Ensure that threads and tasks performing blocking operations can be terminated, to the thread pool.

public final class PoolService {
  // ...
}

public final class SocketReader implements Runnable {
  private final SocketChannel sc;
  // ...
}

Exceptions

EX1: Tasks that execute without blocking may violate this guideline.

Risk Assessment

Submitting tasks that are not interruptible may preclude the thread pool from shutting down and cause denial of service.

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

[[API 06]] interface ExecutorService
[[Goetz 06]] Chapter 7: Cancellation and shutdown

CON30-J. Do not execute interdependent tasks in a bounded thread pool      11. Concurrency (CON)      CON32-J. Ensure that tasks executing in a thread pool do not fail silently