Java Language Executor, ExecutorService and Thread pools Wait for completion of all tasks in ExecutorService
Example
Let's have a look at various options to wait for completion of tasks submitted to Executor
- ExecutorService
invokeAll()Executes the given tasks, returning a list of Futures holding their status and results when everything is completed.
Example:
import java.util.concurrent.*;
import java.util.*;
public class InvokeAllDemo{
public InvokeAllDemo(){
System.out.println("creating service");
ExecutorService service = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());
List<MyCallable> futureList = new ArrayList<MyCallable>();
for (int i = 0; i < 10; i++){
MyCallable myCallable = new MyCallable((long)i);
futureList.add(myCallable);
}
System.out.println("Start");
try{
List<Future<Long>> futures = service.invokeAll(futureList);
} catch(Exception err){
err.printStackTrace();
}
System.out.println("Completed");
service.shutdown();
}
public static void main(String args[]){
InvokeAllDemo demo = new InvokeAllDemo();
}
class MyCallable implements Callable<Long>{
Long id = 0L;
public MyCallable(Long val){
this.id = val;
}
public Long call(){
// Add your business logic
return id;
}
}
}
-
A synchronization aid that allows one or more threads to wait until a set of operations being performed in other threads completes.
A CountDownLatch is initialized with a given count. The await methods block until the current count reaches zero due to invocations of the
countDown()method, after which all waiting threads are released and any subsequent invocations of await return immediately. This is a one-shot phenomenon -- the count cannot be reset. If you need a version that resets the count, consider using a CyclicBarrier. -
ForkJoinPool or
newWorkStealingPool()in Executors -
Iterate through all
Futureobjects created after submitting toExecutorService -
Recommended way of shutdown from oracle documentation page of ExecutorService:
void shutdownAndAwaitTermination(ExecutorService pool) { pool.shutdown(); // Disable new tasks from being submitted try { // Wait a while for existing tasks to terminate if (!pool.awaitTermination(60, TimeUnit.SECONDS)) { pool.shutdownNow(); // Cancel currently executing tasks // Wait a while for tasks to respond to being cancelled if (!pool.awaitTermination(60, TimeUnit.SECONDS)) System.err.println("Pool did not terminate"); } } catch (InterruptedException ie) { // (Re-)Cancel if current thread also interrupted pool.shutdownNow(); // Preserve interrupt status Thread.currentThread().interrupt(); }shutdown():Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.shutdownNow():Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution.In above example, if your tasks are taking more time to complete, you can change if condition to while condition
Replace
if (!pool.awaitTermination(60, TimeUnit.SECONDS))with
while(!pool.awaitTermination(60, TimeUnit.SECONDS)) { Thread.sleep(60000);}
