CODEWITHSUNDEEP
javamultithreadingconcurrencyexecutor
Rus Paul Adrian
Rus Paul Adrian

Reputation: 53

Java Multi-Thread Executor InvokeAll Problems

The code I'm having problems with is:

Executor executor = (Executor) callList;

    List<ProgState> newProgList = executor.invokeAll(callList).stream()
            .map(future -> {try {return future.get();} catch(Exception e){e.printStackTrace();}})
            .filter(p -> p!=null).collect(Collectors.toList());

The method invokeAll(List>) is undefined for the type Executor

I am told I should use an executor like the one in the code snippet.

The Callables are defined within the following code:

List<Callable<ProgState>> callList = (List<Callable<ProgState>>) lst.stream()
            .map(p -> ((Callable<ProgState>)(() -> {return p.oneStep();})))
            .collect(Collectors.toList());

Here is the teacher's code:

//prepare the list of callables

 List<Callable<PrgState>> callList = prgList.stream().map(p -> (() -> {return p.oneStep();})).collect(Collectors.toList());

//start the execution of the callables
//it returns the list of new created threads

List<PrgState> newPrgList = executor.invokeAll(callList).stream()
.map(future -> { try {
 return future.get();
 }
 catch(Exception e) {

 //here you can treat the possible
 // exceptions thrown by statements
 // execution

 }
 })
.filter(p -> p!=null).collect(Collectors.toList());


//add the new created threads to the list of existing threads

 prgList.addAll(newPrgList);

Upvotes: 0

Views: 827

Answers (2)

Peter Lawrey
Peter Lawrey

Reputation: 533492

If you can use stream(), why not parallelStream() as it would be much simpler.

 List<PrgState> prgStates = prgList.parallelStream()
                                   .map(p -> p.oneStep())
                                   .collect(Collectors.toList());

This way you have no thread pool to configure, start or stop when finished.

Some might suggest that parallelStream() was the main reason for adding Stream and lambdas to Java 8 in the first place. ;)

Upvotes: 2

SMA
SMA

Reputation: 37023

You can't cast list of Callables with ExecutorService. You need to define ExecutorService which will inturn pick up callables and execute them in one or multiple threads in parallel.

This is what i think you are after:

ExecutorService executor = Executors.newCachedThreadPool();//change executor type as per your need.
List<ProgState> newProgList = executor.invokeAll(callList).stream().map(future -> {...

Upvotes: 1

Related Questions