ExecutorService FixedThreadPool as a shared parameter not running in parallel












1














I am trying to use fixed thread pool in Java 8 which works perfect as long as it stays within the same function. Once I try sharing the executor as a parameter, it never runs in parallel.



This works great:



```



public static void test2() {

ExecutorService executor = Executors.newFixedThreadPool(2);
try {
CompletionService<Integer> myCompletionService =
new ExecutorCompletionService<Integer>(executor);


myCompletionService.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 123;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});


CompletionService<Integer> myCompletionService2 =
new ExecutorCompletionService<Integer>(executor);
myCompletionService2.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 654;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});

Future<Integer> myFuture = myCompletionService.take();
Integer x = myFuture.get();
System.out.println("Result = " + x);

Future<Integer> myFuture2 = myCompletionService2.take();
Integer y = myFuture2.get();
System.out.println("Result = " + y);

executor.shutdown();
} catch (InterruptedException | ExecutionException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
```


But once I move these into three functions like:



```



static Integer t1(ExecutorService executor) throws InterruptedException, ExecutionException {
CompletionService<Integer> myCompletionService =
new ExecutorCompletionService<Integer>(executor);


myCompletionService.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 123;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});
Future<Integer> myFuture = myCompletionService.take();
return myFuture.get();
}

static Integer t2(ExecutorService executor) throws InterruptedException, ExecutionException {
CompletionService<Integer> myCompletionService2 =
new ExecutorCompletionService<Integer>(executor);


myCompletionService2.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 456;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});
Future<Integer> myFuture2 = myCompletionService2.take();
return myFuture2.get();
}

static void test3() {
ExecutorService executor = Executors.newFixedThreadPool(5);
try {
Integer x = t1(executor);
Integer y = t2(executor);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
executor.shutdown();
}


```
Now test3 will take 10 seconds, where I expected it to be the same as the top one which should take 5 seconds if things are running in parallel.,










share|improve this question






















  • The entire use of CompletionService is obsolete here. You can call submit directly on the ExecutorService and it returns the Future.
    – Holger
    Nov 21 at 7:58
















1














I am trying to use fixed thread pool in Java 8 which works perfect as long as it stays within the same function. Once I try sharing the executor as a parameter, it never runs in parallel.



This works great:



```



public static void test2() {

ExecutorService executor = Executors.newFixedThreadPool(2);
try {
CompletionService<Integer> myCompletionService =
new ExecutorCompletionService<Integer>(executor);


myCompletionService.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 123;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});


CompletionService<Integer> myCompletionService2 =
new ExecutorCompletionService<Integer>(executor);
myCompletionService2.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 654;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});

Future<Integer> myFuture = myCompletionService.take();
Integer x = myFuture.get();
System.out.println("Result = " + x);

Future<Integer> myFuture2 = myCompletionService2.take();
Integer y = myFuture2.get();
System.out.println("Result = " + y);

executor.shutdown();
} catch (InterruptedException | ExecutionException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
```


But once I move these into three functions like:



```



static Integer t1(ExecutorService executor) throws InterruptedException, ExecutionException {
CompletionService<Integer> myCompletionService =
new ExecutorCompletionService<Integer>(executor);


myCompletionService.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 123;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});
Future<Integer> myFuture = myCompletionService.take();
return myFuture.get();
}

static Integer t2(ExecutorService executor) throws InterruptedException, ExecutionException {
CompletionService<Integer> myCompletionService2 =
new ExecutorCompletionService<Integer>(executor);


myCompletionService2.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 456;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});
Future<Integer> myFuture2 = myCompletionService2.take();
return myFuture2.get();
}

static void test3() {
ExecutorService executor = Executors.newFixedThreadPool(5);
try {
Integer x = t1(executor);
Integer y = t2(executor);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
executor.shutdown();
}


```
Now test3 will take 10 seconds, where I expected it to be the same as the top one which should take 5 seconds if things are running in parallel.,










share|improve this question






















  • The entire use of CompletionService is obsolete here. You can call submit directly on the ExecutorService and it returns the Future.
    – Holger
    Nov 21 at 7:58














1












1








1


1





I am trying to use fixed thread pool in Java 8 which works perfect as long as it stays within the same function. Once I try sharing the executor as a parameter, it never runs in parallel.



This works great:



```



public static void test2() {

ExecutorService executor = Executors.newFixedThreadPool(2);
try {
CompletionService<Integer> myCompletionService =
new ExecutorCompletionService<Integer>(executor);


myCompletionService.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 123;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});


CompletionService<Integer> myCompletionService2 =
new ExecutorCompletionService<Integer>(executor);
myCompletionService2.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 654;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});

Future<Integer> myFuture = myCompletionService.take();
Integer x = myFuture.get();
System.out.println("Result = " + x);

Future<Integer> myFuture2 = myCompletionService2.take();
Integer y = myFuture2.get();
System.out.println("Result = " + y);

executor.shutdown();
} catch (InterruptedException | ExecutionException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
```


But once I move these into three functions like:



```



static Integer t1(ExecutorService executor) throws InterruptedException, ExecutionException {
CompletionService<Integer> myCompletionService =
new ExecutorCompletionService<Integer>(executor);


myCompletionService.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 123;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});
Future<Integer> myFuture = myCompletionService.take();
return myFuture.get();
}

static Integer t2(ExecutorService executor) throws InterruptedException, ExecutionException {
CompletionService<Integer> myCompletionService2 =
new ExecutorCompletionService<Integer>(executor);


myCompletionService2.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 456;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});
Future<Integer> myFuture2 = myCompletionService2.take();
return myFuture2.get();
}

static void test3() {
ExecutorService executor = Executors.newFixedThreadPool(5);
try {
Integer x = t1(executor);
Integer y = t2(executor);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
executor.shutdown();
}


```
Now test3 will take 10 seconds, where I expected it to be the same as the top one which should take 5 seconds if things are running in parallel.,










share|improve this question













I am trying to use fixed thread pool in Java 8 which works perfect as long as it stays within the same function. Once I try sharing the executor as a parameter, it never runs in parallel.



This works great:



```



public static void test2() {

ExecutorService executor = Executors.newFixedThreadPool(2);
try {
CompletionService<Integer> myCompletionService =
new ExecutorCompletionService<Integer>(executor);


myCompletionService.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 123;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});


CompletionService<Integer> myCompletionService2 =
new ExecutorCompletionService<Integer>(executor);
myCompletionService2.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 654;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});

Future<Integer> myFuture = myCompletionService.take();
Integer x = myFuture.get();
System.out.println("Result = " + x);

Future<Integer> myFuture2 = myCompletionService2.take();
Integer y = myFuture2.get();
System.out.println("Result = " + y);

executor.shutdown();
} catch (InterruptedException | ExecutionException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
```


But once I move these into three functions like:



```



static Integer t1(ExecutorService executor) throws InterruptedException, ExecutionException {
CompletionService<Integer> myCompletionService =
new ExecutorCompletionService<Integer>(executor);


myCompletionService.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 123;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});
Future<Integer> myFuture = myCompletionService.take();
return myFuture.get();
}

static Integer t2(ExecutorService executor) throws InterruptedException, ExecutionException {
CompletionService<Integer> myCompletionService2 =
new ExecutorCompletionService<Integer>(executor);


myCompletionService2.submit(()-> {
try {
TimeUnit.SECONDS.sleep(5);
return 456;
}
catch (InterruptedException e) {
throw new IllegalStateException("task interrupted", e);
}
});
Future<Integer> myFuture2 = myCompletionService2.take();
return myFuture2.get();
}

static void test3() {
ExecutorService executor = Executors.newFixedThreadPool(5);
try {
Integer x = t1(executor);
Integer y = t2(executor);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
executor.shutdown();
}


```
Now test3 will take 10 seconds, where I expected it to be the same as the top one which should take 5 seconds if things are running in parallel.,







java java-8 threadpool






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Nov 20 at 21:47









Mohy Eldeen

648619




648619












  • The entire use of CompletionService is obsolete here. You can call submit directly on the ExecutorService and it returns the Future.
    – Holger
    Nov 21 at 7:58


















  • The entire use of CompletionService is obsolete here. You can call submit directly on the ExecutorService and it returns the Future.
    – Holger
    Nov 21 at 7:58
















The entire use of CompletionService is obsolete here. You can call submit directly on the ExecutorService and it returns the Future.
– Holger
Nov 21 at 7:58




The entire use of CompletionService is obsolete here. You can call submit directly on the ExecutorService and it returns the Future.
– Holger
Nov 21 at 7:58












1 Answer
1






active

oldest

votes


















2














In t1 after submitting you are calling get() and get blocked, so you exit from t1 only when first task is finished (after 5 secs).



In first example you submit both tasks so they starting executing in separate threads and then only call get() to block and wait for result.






share|improve this answer





















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    1 Answer
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    1 Answer
    1






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    2














    In t1 after submitting you are calling get() and get blocked, so you exit from t1 only when first task is finished (after 5 secs).



    In first example you submit both tasks so they starting executing in separate threads and then only call get() to block and wait for result.






    share|improve this answer


























      2














      In t1 after submitting you are calling get() and get blocked, so you exit from t1 only when first task is finished (after 5 secs).



      In first example you submit both tasks so they starting executing in separate threads and then only call get() to block and wait for result.






      share|improve this answer
























        2












        2








        2






        In t1 after submitting you are calling get() and get blocked, so you exit from t1 only when first task is finished (after 5 secs).



        In first example you submit both tasks so they starting executing in separate threads and then only call get() to block and wait for result.






        share|improve this answer












        In t1 after submitting you are calling get() and get blocked, so you exit from t1 only when first task is finished (after 5 secs).



        In first example you submit both tasks so they starting executing in separate threads and then only call get() to block and wait for result.







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Nov 20 at 21:53









        art

        717




        717






























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