The use case is there is a set of methods which need to be executed based on whether the previous one has returned true or not.
For example:
class Test {
boolean method1() {...}
boolean method2() {...}
boolean method3() {...}
...
void callAll() {
if(method1()) {
if(method2() {
if(method3() {
...
}
}
} else {
error();
}
}
}
There has to be an else for all the ifs.
Is there a better way of handling this scenario?
I would just do it like this:
void callAll(){
if(method1() && method2() && method3()){
// all passed
} else {
error();
}
}
Java short-circuits the && logical operation so failure in a previous method here will prevent running the next one.
If in error() you need to know which of the methods failed, you could declare an error message field for storing the information within the class and set its value corresponding the failure:
private String errorMessage;
//...
boolean method2() {
// something went wrong
errorMessage = "Failed to do method2 stuff";
}
Are more elegant way to achieve the same would be to use the Chain of responsibility design pattern and encapsulate the boolean methods in their own handler objects. Doing this would however require more refactoring to the code you currently have and more information about your specific use case.
It's easy enough to write your own varargs method to do this:
public static void run(Supplier<Boolean>... methods) {
for (Supplier<Boolean> method : methods) {
if (!method.get()) return;
}
}
Sample usage:
run(this::method1, this::method2, this::method3);
You can use some form of Observable pattern for these kind of thins too. In most normal cases it seems a bit silly to implement it but otherwise a great way to decouple code from control structures if you have a lot of these. Note that ObservableBoolean is an Android class, but just showing the logic here:
ObservableBoolean a = new ObservableBoolean();
ObservableBoolean b = new ObservableBoolean();
public void call() {
a.addOnPropertyChangedCallback(new OnPropertyChangedCallback() {
#Override
public void onPropertyChanged(android.databinding.Observable sender, int propertyId) {
method2();
}
});
b.addOnPropertyChangedCallback(new OnPropertyChangedCallback() {
#Override
public void onPropertyChanged(android.databinding.Observable sender, int propertyId) {
//..you end the "chain" here
}
});
method1();
}
void method1() {
if(true) {
a.set(true);
}
else {
b.set(false);
}
}
void method2() {
if(true) {
b.set(true);
}
else {
b.set(false);
}
}
I use this technique - although some would find it odd.
boolean method1() {
System.out.println("method1");
return true;
}
boolean method2() {
System.out.println("method2");
return false;
}
boolean method3() {
System.out.println("method3");
return true;
}
void callAll() {
boolean success = method1();
success = success ? method2() : success;
success = success ? method3() : success;
if (success) {
System.out.println("Success");
} else {
System.out.println("Failed");
}
}
I could suggest you to use RX approach, with rxjava it should look like
public boolean test1() {
Log.d("TESTIT", "test1 called");
return true;
}
public boolean test2() {
Log.d("TESTIT", "test2 called");
return true;
}
public boolean test3() {
Log.d("TESTIT", "test3 called");
return false;
}
public boolean test4() {
Log.d("TESTIT", "test4 called");
return true;
}
public boolean elseMethod(boolean result) {
if (result) return true;
else {
Log.d("TESTIT", "ELSE");
}
return false;
}
public void chainedCallback() {
Observable.just(test1())
.filter(this::elseMethod)
.flatMap(aBoolean -> Observable.just(test2()))
.filter(this::elseMethod)
.flatMap(aBoolean -> Observable.just(test3()))
.filter(this::elseMethod)
.flatMap(aBoolean -> Observable.just(test4()))
.filter(this::elseMethod)
.subscribe();
}
call for chainedCallback() will print
test1 called
test2 called
test3 called
ELSE
You define a class that holds an action (calling one of the methods) and with a corresponding failure handler (the else block of an if call)
public static class ActionWithFailureHandler {
private Supplier<Boolean> action;
private Runnable failureHandler;
public ActionWithFailureHandler(Supplier<Boolean> action, Runnable failureHandler) {
this.action = action;
this.failureHandler = failureHandler;
}
//Getters for the instance variables
}
You make a list of the above and call each of the actions till one of the following happens
One of the actions fails (i.,e one of the method returns false). In that case, you need to execute the failureHandler corresponding to that action.
All actions pass. In this case, execute the successHandler (the logic that you execute when all methods return true).
private static void callAll(List<ActionWithFailureHandler> actionWithFailureHandlers, Runnable successHandler) {
actionWithFailureHandlers.stream()
.filter(actionWithFailureHandler -> !actionWithFailureHandler.getAction().get())
.findFirst() //Find first failing action
.map(ActionWithFailureHandler::getFailureHandler)
.orElse(successHandler)
.run(); //You might be running either the successHandler or the failureHandler for the first failed action
}
Driver code:
public static void main(String[] args) {
Test test = new Test();
List<ActionWithFailureHandler> actionWithFailureHandlers = com.google.common.collect.ImmutableList.of(
new ActionWithFailureHandler(test::method1, () -> System.out.println("Method 1 returned false")),
new ActionWithFailureHandler(test::method2, () -> System.out.println("Method 2 returned false")),
new ActionWithFailureHandler(test::method3, () -> System.out.println("Method 3 returned false"))
);
callAll(actionWithFailureHandlers, () -> System.out.println("All returned true"));
}
Exception firstly comes to my mind, but see the link below to learn more about its performance hit.
Original answer. I would do..
public class MyException extends Exception
{
}
public void doAll()
{
try
{
method1();
method2();
method3();
}catch (MyException e)
{
error();
}
}
And let's assume that method1, method2, and method3 throws MyException when it fails.
Though it does not fit your question, it is a good pattern to use Exceptions.
public class Helper
{
public Helper(Method m)
{
this.method=m;
}
public void Do() throws MyException
{
if(method.invoke()==false)
throw new MyException ();
}
}
Using this class,
public void doAll()
{
Helper [] helpers={new Helper(this::method1), new Helper(this::method2), new Helper (this::method3)};
try
{
for(Helper helper:helpers)
{
helper.Do();
}
}catch (MyException e)
{
error();
}
}
But
according to the comment of #dilix and the link, it can be a performance-expensive strategy.
So let's use them only for their purpose.
I am currently creating a database util class but my mongodb driver is async, my question now is how can I sync him? My current try looks something like this:
public boolean isBanIDFree(String banid) {
boolean value = false;
Thread thread = Thread.currentThread();
MongoCollection<Document> collection = database.getCollection("Bans");
collection.find(new Document("ID", banid)).first(new SingleResultCallback<Document>() {
#Override
public void onResult(Document result, Throwable t) {
if(result == null) {
value = true;
}
thread.notify();
}
});
try {
thread.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
return value;
}
but I can't edit the veriable value in the onResult Callback, how can I bypass this. i want to return a boolean and want the calling thread to wait until I got the response from the database
Variables used in anonymous classes must be effectively final.
That means you cannot assign them to something else, but you can call a setter on them.
So, you can do something like:
import java.util.concurrent.CompletableFuture;
public class Main {
public static void main(String[] args) {
BooleanWrapper b = new BooleanWrapper();
CompletableFuture.runAsync(() -> b.setValue(true));
// ...
}
private static class BooleanWrapper {
private boolean value;
public boolean getValue() {
return value;
}
public void setValue(boolean value) {
this.value = value;
}
}
}
I have a problem with this async call:
public class myClass {
protected final int idObj;
public void myMethod() {
myService.getObj( new AsyncCallback<List<Object>>() {
#Override
public void onFailure(Throwable caught) {
}
#Override
public void onSuccess(List<Object> listObject) {
idObj = listObject.get(0).getIdObj();
}
});
if(idObj == 1) {
//do something
}
}
}
The value idObj is equal zero at the first time and this if block isn't execute.
How to avoid this?
It's an asynchronous call, that means that the code executed in your onSuccess method will be executed later.
So the if statement is executed but at this time your value still 0.
You should put your if statement in the onSuccess method.
I whould like to block a method execution from more thab 3 threads. The method can be executed recursively. I have following agly code. Can I achive this by using better way?
private static class MyHolder {
private static Semaphore limitThreadsSemaphore = new Semaphore(3);
private static Set<Thread> asquiredThreads = new HashSet<Thread>();
}
#Override
public void someMethod() {
if (!MyHolder.asquiredThreads.contains(Thread.currentThread())) {
synchronized (MyHolder.asquiredThreads) {
if (!MyHolder.asquiredThreads.contains(Thread.currentThread())) {
try {
MyHolder.limitThreadsSemaphore.acquire();
MyHolder.asquiredThreads.add(Thread.currentThread());
} finally {
MyHolder.limitThreadsSemaphore.release();
MyHolder.asquiredThreads.remove(Thread.currentThread());
}
}
}
}
return super.someMethod();
}
Thanks.
The simplest approach would be to refactor the recursive method to be private and then have the public method unconditionally acquire the semaphore, call the private method and then release the semaphore again. The recursive calls route straight to the private method so don't go through the semaphore guard code.
If that is not an option then the simplest approach I can think of would be to use a ThreadLocal flag
ThreadLocal<Object> alreadyIn = new ThreadLocal<>();
public void someMethod() {
boolean needSem = (alreadyIn.get() == null);
if(needSem) {
semaphore.acquire();
alreadyIn.set(new Object());
}
try {
// do stuff
} finally {
if(needSem) {
alreadyIn.remove();
semaphore.release();
}
}
}
I guess "someMethod" is the method you want to block execution,yeah?. Why don'y you do this? :
private static class MyHolder {
private static Semaphore limitThreadsSemaphore = new Semaphore(3);
public boolean semaphoreAdquired = false; //Make it private
public Semaphore getSemaphore()
{
return limitThreadsSemaphore;
}
}
#Override
public void someMethod() {
boolean ReleaseSemaphore = false;
if(!semaphoreAdquired)
{
MyHolder.getSemaphore().acquire();
semaphoreAdquired = true;
ReleaseSemaphore = true;
}
super.someMethod();
if(ReleaseSemaphore)
{
MyHolder.getSemaphore().release();
semaphoreAdquired = false;
}
}
Based on the documentation for Semaphor, this should be achievable using only acquire() and release() around the critical section. Also, you should be able to put the semaphor in the current class, no need for a separate class to contain the Semaphor.
private static Semaphore limitThreadsSemaphore = new Semaphore(3);
#Override
public void someMethod() {
limitThreadsSemaphore.acquire();
// do work.
limitThreadsSemaphore.release();
}
Update: If you need to call a method recursively within a thread, then the easiest way is to use a helper method to acquire the semaphor, and then invoke the recursive method from that helper method after acquiring the sempahor. You would call the helper instead of the original method in all the initial calls.
private static Semaphore limitThreadsSemaphore = new Semaphore(3);
public void someMethodHelper() {
limitThreadsSemaphore.acquire();
someMethod();
limitThreadsSemaphore.release();
}
#Override
public void someMethod() {
// do work, with recursive calls.
}
This question is related to my question on existing coroutine implementations in Java. If, as I suspect, it turns out that there is no full implementation of coroutines currently available in Java, what would be required to implement them?
As I said in that question, I know about the following:
You can implement "coroutines" as threads/thread pools behind the scenes.
You can do tricksy things with JVM bytecode behind the scenes to make coroutines possible.
The so-called "Da Vinci Machine" JVM implementation has primitives that make coroutines doable without
bytecode manipulation.
There are various JNI-based approaches to coroutines also possible.
I'll address each one's deficiencies in turn.
Thread-based coroutines
This "solution" is pathological. The whole point of coroutines is to avoid the overhead of threading, locking, kernel scheduling, etc. Coroutines are supposed to be light and fast and to execute only in user space. Implementing them in terms of full-tilt threads with tight restrictions gets rid of all the advantages.
JVM bytecode manipulation
This solution is more practical, albeit a bit difficult to pull off. This is roughly the same as jumping down into assembly language for coroutine libraries in C (which is how many of them work) with the advantage that you have only one architecture to worry about and get right.
It also ties you down to only running your code on fully-compliant JVM stacks (which means, for example, no Android) unless you can find a way to do the same thing on the non-compliant stack. If you do find a way to do this, however, you have now doubled your system complexity and testing needs.
The Da Vinci Machine
The Da Vinci Machine is cool for experimentation, but since it is not a standard JVM its features aren't going to be available everywhere. Indeed I suspect most production environments would specifically forbid the use of the Da Vinci Machine. Thus I could use this to make cool experiments but not for any code I expect to release to the real world.
This also has the added problem similar to the JVM bytecode manipulation solution above: won't work on alternative stacks (like Android's).
JNI implementation
This solution renders the point of doing this in Java at all moot. Each combination of CPU and operating system requires independent testing and each is a point of potentially frustrating subtle failure. Alternatively, of course, I could tie myself down to one platform entirely but this, too, makes the point of doing things in Java entirely moot.
So...
Is there any way to implement coroutines in Java without using one of these four techniques? Or will I be forced to use the one of those four that smells the least (JVM manipulation) instead?
Edited to add:
Just to ensure that confusion is contained, this is a related question to my other one, but not the same. That one is looking for an existing implementation in a bid to avoid reinventing the wheel unnecessarily. This one is a question relating to how one would go about implementing coroutines in Java should the other prove unanswerable. The intent is to keep different questions on different threads.
I would take a look at this: http://www.chiark.greenend.org.uk/~sgtatham/coroutines.html, its pretty interesting and should provide a good place to start. But of course we are using Java so we can do better (or maybe worse because there are no macros :))
From my understanding with coroutines you usually have a producer and a consumer coroutine (or at least this is the most common pattern). But semantically you don't want the producer to call the consumer or visa-versa because this introduces an asymmetry. But given the way stack based languages work we will need to have someone do the calling.
So here is a very simple type hierarchy:
public interface CoroutineProducer<T>
{
public T Produce();
public boolean isDone();
}
public interface CoroutineConsumer<T>
{
public void Consume(T t);
}
public class CoroutineManager
{
public static Execute<T>(CoroutineProducer<T> prod, CoroutineConsumer<T> con)
{
while(!prod.IsDone()) // really simple
{
T d = prod.Produce();
con.Consume(d);
}
}
}
Now of course the hard part is implementing the interfaces, in particular it is difficult to break a computation into individual steps. For this you would probably want a whole other set of persistent control structures. The basic idea is that we want to simulate non-local transfer of control (in the end its kinda like we're simulating a goto). We basically want to move away from using the stack and the pc (program-counter) by keeping the state of our current operations in the heap instead of on the stack. Therefore we are going to need a bunch of helper classes.
For example:
Let's say that in an ideal world you wanted to write a consumer that looked like this (psuedocode):
boolean is_done;
int other_state;
while(!is_done)
{
//read input
//parse input
//yield input to coroutine
//update is_done and other_state;
}
we need to abstract the local variable like is_doneand other_state and we need to abstract the while loop itself because our yield like operation is not going to be using the stack. So let's create a while loop abstraction and associated classes:
enum WhileState {BREAK, CONTINUE, YIELD}
abstract class WhileLoop<T>
{
private boolean is_done;
public boolean isDone() { return is_done;}
private T rval;
public T getReturnValue() {return rval;}
protected void setReturnValue(T val)
{
rval = val;
}
public T loop()
{
while(true)
{
WhileState state = execute();
if(state == WhileState.YIELD)
return getReturnValue();
else if(state == WhileState.BREAK)
{
is_done = true;
return null;
}
}
}
protected abstract WhileState execute();
}
The Basic trick here is to move local variables to be class variables and turn scope blocks into classes which gives us the ability to 're-enter' our 'loop' after yielding our return value.
Now to implement our producer
public class SampleProducer : CoroutineProducer<Object>
{
private WhileLoop<Object> loop;//our control structures become state!!
public SampleProducer()
{
loop = new WhileLoop()
{
private int other_state;//our local variables become state of the control structure
protected WhileState execute()
{
//this implements a single iteration of the loop
if(is_done) return WhileState.BREAK;
//read input
//parse input
Object calcluated_value = ...;
//update is_done, figure out if we want to continue
setReturnValue(calculated_value);
return WhileState.YIELD;
}
};
}
public Object Produce()
{
Object val = loop.loop();
return val;
}
public boolean isDone()
{
//we are done when the loop has exited
return loop.isDone();
}
}
Similar tricks could be done for other basic control flow structures. You would ideally build up a library of these helper classes and then use them to implement these simple interfaces which would ultimately give you the semantics of co-routines. I'm sure everything I've written here can be generalized and expanded upon greatly.
I'd suggest to look at Kotlin coroutines on JVM. It falls into a different category, though. There is no byte-code manipulation involved and it works on Android, too. However, you will have to write your coroutines in Kotlin. The upside is that Kotlin is designed for interoperability with Java in mind, so you can still continue to use all your Java libraries and freely combine Kotlin and Java code in the same project, even putting them side-by-side in the same directories and packages.
This Guide to kotlinx.coroutines provides many more examples, while the coroutines design document explains all the motivation, use-cases and implementation details.
Kotlin uses the following approach for co-routines
(from https://kotlinlang.org/docs/reference/coroutines.html):
Coroutines are completely implemented through a compilation technique (no support from the VM or OS side is required), and suspension works through code transformation. Basically, every suspending function (optimizations may apply, but we'll not go into this here) is transformed to a state machine where states correspond to suspending calls. Right before a suspension, the next state is stored in a field of a compiler-generated class along with relevant local variables, etc. Upon resumption of that coroutine, local variables are restored and the state machine proceeds from the state right after suspension.
A suspended coroutine can be stored and passed around as an object that keeps its suspended state and locals. The type of such objects is Continuation, and the overall code transformation described here corresponds to the classical Continuation-passing style. Consequently, suspending functions take an extra parameter of type Continuation under the hood.
Check out the design document at https://github.com/Kotlin/kotlin-coroutines/blob/master/kotlin-coroutines-informal.md
I just came across this question and just want to mention that i think it might be possible to implement coroutines or generators in a similar way C# does. That said i don't actually use Java but the CIL has quite similar limitations as the JVM has.
The yield statement in C# is a pure language feature and is not part of the CIL bytecode. The C# compiler just creates a hidden private class for each generator function. If you use the yield statement in a function it has to return an IEnumerator or an IEnumerable. The compiler "packs" your code into a statemachine-like class.
The C# compiler might use some "goto's" in the generated code to make the conversion into a statemachine easier. I don't know the capabilities of Java bytecode and if there's something like a plain unconditional jump, but at "assembly level" it's usually possible.
As already mentioned this feature has to be implemented in the compiler. Because i have only little knowledge about Java and it's compiler i can't tell if it's possible to alter / extend the compiler, maybe with a "preprocessor" or something.
Personally i love coroutines. As a Unity games developer i use them quite often. Because i play alot of Minecraft with ComputerCraft i was curious why coroutines in Lua (LuaJ) are implemented with threads.
There is also Quasar for Java and Project Loom at Oracle where extensions are made to the JVM for fibers and continuations. Here is a presentation of Loom on Youtoube. There are several more. Easy to find with a little searching.
Project Loom: https://jdk.java.net/loom/ introduce Continuations to Java.
An example:
static final ContinuationScope scope=new ContinuationScope("TST");
public static void main(String[] args) {
example1();
}
// *********************************************************************
// *** EXAMPLE 1: Co-routine with three active phases:
// *********************************************************************
public static void example1() {
Continuation coroutine=new Continuation(scope,new Runnable() {
public void run() {
System.out.println("Part 1 - Statements");
Continuation.yield(scope); // DETACH 1
System.out.println("Part 2 - Statements");
Continuation.yield(scope); // DETACH 2
System.out.println("Part 3 - Statements");
}});
coroutine.run(); // Vil utføre Part 1.
System.out.println("Returns here after first DETACH(Yield)");
coroutine.run(); // Vil utføre Part 2.
System.out.println("Returns here after second DETACH(Yield)");
coroutine.run(); // Vil utføre Part 3.
System.out.println("Returns here after 'FINAL END'");
System.out.println("Next line should be: IllegalStateException: Continuation terminated");
coroutine.run(); // IllegalStateException: Continuation terminated
}
I have a Coroutine class that I use in Java. It is based on threads and using threads has the advantage of allowing parallel operation, which on multicore machines can be an advantage. Therefore you might want to consider a thread based approach.
There's an another choice is here for Java6+
A pythonic coroutine implementation:
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;
class CorRunRAII {
private final List<WeakReference<? extends CorRun>> resources = new ArrayList<>();
public CorRunRAII add(CorRun resource) {
if (resource == null) {
return this;
}
resources.add(new WeakReference<>(resource));
return this;
}
public CorRunRAII addAll(List<? extends CorRun> arrayList) {
if (arrayList == null) {
return this;
}
for (CorRun corRun : arrayList) {
add(corRun);
}
return this;
}
#Override
protected void finalize() throws Throwable {
super.finalize();
for (WeakReference<? extends CorRun> corRunWeakReference : resources) {
CorRun corRun = corRunWeakReference.get();
if (corRun != null) {
corRun.stop();
}
}
}
}
class CorRunYieldReturn<ReceiveType, YieldReturnType> {
public final AtomicReference<ReceiveType> receiveValue;
public final LinkedBlockingDeque<AtomicReference<YieldReturnType>> yieldReturnValue;
CorRunYieldReturn(AtomicReference<ReceiveType> receiveValue, LinkedBlockingDeque<AtomicReference<YieldReturnType>> yieldReturnValue) {
this.receiveValue = receiveValue;
this.yieldReturnValue = yieldReturnValue;
}
}
interface CorRun<ReceiveType, YieldReturnType> extends Runnable, Callable<YieldReturnType> {
boolean start();
void stop();
void stop(final Throwable throwable);
boolean isStarted();
boolean isEnded();
Throwable getError();
ReceiveType getReceiveValue();
void setResultForOuter(YieldReturnType resultForOuter);
YieldReturnType getResultForOuter();
YieldReturnType receive(ReceiveType value);
ReceiveType yield();
ReceiveType yield(YieldReturnType value);
<TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(final CorRun<TargetReceiveType, TargetYieldReturnType> another);
<TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(final CorRun<TargetReceiveType, TargetYieldReturnType> another, final TargetReceiveType value);
}
abstract class CorRunSync<ReceiveType, YieldReturnType> implements CorRun<ReceiveType, YieldReturnType> {
private ReceiveType receiveValue;
public final List<WeakReference<CorRun>> potentialChildrenCoroutineList = new ArrayList<>();
// Outside
private AtomicBoolean isStarted = new AtomicBoolean(false);
private AtomicBoolean isEnded = new AtomicBoolean(false);
private Throwable error;
private YieldReturnType resultForOuter;
#Override
public boolean start() {
boolean isStarted = this.isStarted.getAndSet(true);
if ((! isStarted)
&& (! isEnded())) {
receive(null);
}
return isStarted;
}
#Override
public void stop() {
stop(null);
}
#Override
public void stop(Throwable throwable) {
isEnded.set(true);
if (throwable != null) {
error = throwable;
}
for (WeakReference<CorRun> weakReference : potentialChildrenCoroutineList) {
CorRun child = weakReference.get();
if (child != null) {
child.stop();
}
}
}
#Override
public boolean isStarted() {
return isStarted.get();
}
#Override
public boolean isEnded() {
return isEnded.get();
}
#Override
public Throwable getError() {
return error;
}
#Override
public ReceiveType getReceiveValue() {
return receiveValue;
}
#Override
public void setResultForOuter(YieldReturnType resultForOuter) {
this.resultForOuter = resultForOuter;
}
#Override
public YieldReturnType getResultForOuter() {
return resultForOuter;
}
#Override
public synchronized YieldReturnType receive(ReceiveType value) {
receiveValue = value;
run();
return getResultForOuter();
}
#Override
public ReceiveType yield() {
return yield(null);
}
#Override
public ReceiveType yield(YieldReturnType value) {
resultForOuter = value;
return receiveValue;
}
#Override
public <TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(CorRun<TargetReceiveType, TargetYieldReturnType> another) {
return yieldFrom(another, null);
}
#Override
public <TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(CorRun<TargetReceiveType, TargetYieldReturnType> another, TargetReceiveType value) {
if (another == null || another.isEnded()) {
throw new RuntimeException("Call null or isEnded coroutine");
}
potentialChildrenCoroutineList.add(new WeakReference<CorRun>(another));
synchronized (another) {
boolean isStarted = another.start();
boolean isJustStarting = ! isStarted;
if (isJustStarting && another instanceof CorRunSync) {
return another.getResultForOuter();
}
return another.receive(value);
}
}
#Override
public void run() {
try {
this.call();
}
catch (Exception e) {
e.printStackTrace();
stop(e);
return;
}
}
}
abstract class CorRunThread<ReceiveType, YieldReturnType> implements CorRun<ReceiveType, YieldReturnType> {
private final ExecutorService childExecutorService = newExecutorService();
private ExecutorService executingOnExecutorService;
private static final CorRunYieldReturn DUMMY_COR_RUN_YIELD_RETURN = new CorRunYieldReturn(new AtomicReference<>(null), new LinkedBlockingDeque<AtomicReference>());
private final CorRun<ReceiveType, YieldReturnType> self;
public final List<WeakReference<CorRun>> potentialChildrenCoroutineList;
private CorRunYieldReturn<ReceiveType, YieldReturnType> lastCorRunYieldReturn;
private final LinkedBlockingDeque<CorRunYieldReturn<ReceiveType, YieldReturnType>> receiveQueue;
// Outside
private AtomicBoolean isStarted = new AtomicBoolean(false);
private AtomicBoolean isEnded = new AtomicBoolean(false);
private Future<YieldReturnType> future;
private Throwable error;
private final AtomicReference<YieldReturnType> resultForOuter = new AtomicReference<>();
CorRunThread() {
executingOnExecutorService = childExecutorService;
receiveQueue = new LinkedBlockingDeque<>();
potentialChildrenCoroutineList = new ArrayList<>();
self = this;
}
#Override
public void run() {
try {
self.call();
}
catch (Exception e) {
stop(e);
return;
}
stop();
}
#Override
public abstract YieldReturnType call();
#Override
public boolean start() {
return start(childExecutorService);
}
protected boolean start(ExecutorService executorService) {
boolean isStarted = this.isStarted.getAndSet(true);
if (!isStarted) {
executingOnExecutorService = executorService;
future = (Future<YieldReturnType>) executingOnExecutorService.submit((Runnable) self);
}
return isStarted;
}
#Override
public void stop() {
stop(null);
}
#Override
public void stop(final Throwable throwable) {
if (throwable != null) {
error = throwable;
}
isEnded.set(true);
returnYieldValue(null);
// Do this for making sure the coroutine has checked isEnd() after getting a dummy value
receiveQueue.offer(DUMMY_COR_RUN_YIELD_RETURN);
for (WeakReference<CorRun> weakReference : potentialChildrenCoroutineList) {
CorRun child = weakReference.get();
if (child != null) {
if (child instanceof CorRunThread) {
((CorRunThread)child).tryStop(childExecutorService);
}
}
}
childExecutorService.shutdownNow();
}
protected void tryStop(ExecutorService executorService) {
if (this.executingOnExecutorService == executorService) {
stop();
}
}
#Override
public boolean isEnded() {
return isEnded.get() || (
future != null && (future.isCancelled() || future.isDone())
);
}
#Override
public boolean isStarted() {
return isStarted.get();
}
public Future<YieldReturnType> getFuture() {
return future;
}
#Override
public Throwable getError() {
return error;
}
#Override
public void setResultForOuter(YieldReturnType resultForOuter) {
this.resultForOuter.set(resultForOuter);
}
#Override
public YieldReturnType getResultForOuter() {
return this.resultForOuter.get();
}
#Override
public YieldReturnType receive(ReceiveType value) {
LinkedBlockingDeque<AtomicReference<YieldReturnType>> yieldReturnValue = new LinkedBlockingDeque<>();
offerReceiveValue(value, yieldReturnValue);
try {
AtomicReference<YieldReturnType> takeValue = yieldReturnValue.take();
return takeValue == null ? null : takeValue.get();
} catch (InterruptedException e) {
e.printStackTrace();
}
return null;
}
#Override
public ReceiveType yield() {
return yield(null);
}
#Override
public ReceiveType yield(final YieldReturnType value) {
returnYieldValue(value);
return getReceiveValue();
}
#Override
public <TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(final CorRun<TargetReceiveType, TargetYieldReturnType> another) {
return yieldFrom(another, null);
}
#Override
public <TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(final CorRun<TargetReceiveType, TargetYieldReturnType> another, final TargetReceiveType value) {
if (another == null || another.isEnded()) {
throw new RuntimeException("Call null or isEnded coroutine");
}
boolean isStarted = false;
potentialChildrenCoroutineList.add(new WeakReference<CorRun>(another));
synchronized (another) {
if (another instanceof CorRunThread) {
isStarted = ((CorRunThread)another).start(childExecutorService);
}
else {
isStarted = another.start();
}
boolean isJustStarting = ! isStarted;
if (isJustStarting && another instanceof CorRunSync) {
return another.getResultForOuter();
}
TargetYieldReturnType send = another.receive(value);
return send;
}
}
#Override
public ReceiveType getReceiveValue() {
setLastCorRunYieldReturn(takeLastCorRunYieldReturn());
return lastCorRunYieldReturn.receiveValue.get();
}
protected void returnYieldValue(final YieldReturnType value) {
CorRunYieldReturn<ReceiveType, YieldReturnType> corRunYieldReturn = lastCorRunYieldReturn;
if (corRunYieldReturn != null) {
corRunYieldReturn.yieldReturnValue.offer(new AtomicReference<>(value));
}
}
protected void offerReceiveValue(final ReceiveType value, LinkedBlockingDeque<AtomicReference<YieldReturnType>> yieldReturnValue) {
receiveQueue.offer(new CorRunYieldReturn(new AtomicReference<>(value), yieldReturnValue));
}
protected CorRunYieldReturn<ReceiveType, YieldReturnType> takeLastCorRunYieldReturn() {
try {
return receiveQueue.take();
} catch (InterruptedException e) {
e.printStackTrace();
}
return null;
}
protected void setLastCorRunYieldReturn(CorRunYieldReturn<ReceiveType,YieldReturnType> lastCorRunYieldReturn) {
this.lastCorRunYieldReturn = lastCorRunYieldReturn;
}
protected ExecutorService newExecutorService() {
return Executors.newCachedThreadPool(getThreadFactory());
}
protected ThreadFactory getThreadFactory() {
return new ThreadFactory() {
#Override
public Thread newThread(final Runnable runnable) {
Thread thread = new Thread(runnable);
thread.setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
#Override
public void uncaughtException(Thread thread, Throwable throwable) {
throwable.printStackTrace();
if (runnable instanceof CorRun) {
CorRun self = (CorRun) runnable;
self.stop(throwable);
thread.interrupt();
}
}
});
return thread;
}
};
}
}
Now you can use pythonic coroutines in this way
(e.g. fibonacci numbers)
Thread Version:
class Fib extends CorRunThread<Integer, Integer> {
#Override
public Integer call() {
Integer times = getReceiveValue();
do {
int a = 1, b = 1;
for (int i = 0; times != null && i < times; i++) {
int temp = a + b;
a = b;
b = temp;
}
// A pythonic "yield", i.e., it returns `a` to the caller and waits `times` value from the next caller
times = yield(a);
} while (! isEnded());
setResultForOuter(Integer.MAX_VALUE);
return getResultForOuter();
}
}
class MainRun extends CorRunThread<String, String> {
#Override
public String call() {
// The fib coroutine would be recycled by its parent
// (no requirement to call its start() and stop() manually)
// Otherwise, if you want to share its instance and start/stop it manually,
// please start it before being called by yieldFrom() and stop it in the end.
Fib fib = new Fib();
String result = "";
Integer current;
int times = 10;
for (int i = 0; i < times; i++) {
// A pythonic "yield from", i.e., it calls fib with `i` parameter and waits for returned value as `current`
current = yieldFrom(fib, i);
if (fib.getError() != null) {
throw new RuntimeException(fib.getError());
}
if (current == null) {
continue;
}
if (i > 0) {
result += ",";
}
result += current;
}
setResultForOuter(result);
return result;
}
}
Sync(non-thread) version:
class Fib extends CorRunSync<Integer, Integer> {
#Override
public Integer call() {
Integer times = getReceiveValue();
int a = 1, b = 1;
for (int i = 0; times != null && i < times; i++) {
int temp = a + b;
a = b;
b = temp;
}
yield(a);
return getResultForOuter();
}
}
class MainRun extends CorRunSync<String, String> {
#Override
public String call() {
CorRun<Integer, Integer> fib = null;
try {
fib = new Fib();
} catch (Exception e) {
e.printStackTrace();
}
String result = "";
Integer current;
int times = 10;
for (int i = 0; i < times; i++) {
current = yieldFrom(fib, i);
if (fib.getError() != null) {
throw new RuntimeException(fib.getError());
}
if (current == null) {
continue;
}
if (i > 0) {
result += ",";
}
result += current;
}
stop();
setResultForOuter(result);
if (Utils.isEmpty(result)) {
throw new RuntimeException("Error");
}
return result;
}
}
Execution(Both versions will work):
// Run the entry coroutine
MainRun mainRun = new MainRun();
mainRun.start();
// Wait for mainRun ending for 5 seconds
long startTimestamp = System.currentTimeMillis();
while(!mainRun.isEnded()) {
if (System.currentTimeMillis() - startTimestamp > TimeUnit.SECONDS.toMillis(5)) {
throw new RuntimeException("Wait too much time");
}
}
// The result should be "1,1,2,3,5,8,13,21,34,55"
System.out.println(mainRun.getResultForOuter());
Instead of using any other method just create a wrapper class for java
/**
* This class will be used run java code in the kotlin coroutines
* #author : prustyA : 17/06/2022
*/
class CoroutineJava {
//Scope
private val context: CoroutineContext = Dispatchers.IO
private val scope = CoroutineScope(context)
/**
* This method will be used to return current coroutine context
* #author : prustyA : 17/06/2022
*/
fun getContext() = context
/**
* This method will be used to start executing the method block
* #author : prustyA : 17/06/2022
*/
fun launch(block: () -> Unit) {
scope.launch { block() }
}
/**
* This method will be used to change the context and run the block
* #author : prustyA : 17/06/2022
*/
fun launchWithContext(context: CoroutineContext,block: () -> Unit) {
scope.launch {
withContext(context) { block() }
}
}
}