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How do you return a value from a thread?

How do you return a value from a thread?

Return a value from a thread

  1. We have implemented two classes, RetDouble and RetInt that both implement the Callable, the first using as parameter a Double and the second one using as parameter an Integer .
  2. We create an ExecutorService, using newFixedThreadPool(int nThreads) API method of Executors.

How does thread call method return value?

Threads do not really have return values. However, if you create a delegate, you can invoke it asynchronously via the BeginInvoke method. This will execute the method on a thread pool thread. You can get any return value from such as call via EndInvoke .

Can a method return a value?

You declare a method’s return type in its method declaration. Within the body of the method, you use the return statement to return the value. Any method declared void doesn’t return a value and cannot contain a return statement.

Can Run method return value in Java?

The run method of Runnable has return type void and cannot return a value.

How does ExecutorService return value?

2 Answers. Call your getMYInfo(i) in Callable , submit this callable to executor, then wait for competition of Future . You can do that by submitting a Callable , the submit method will then return a Future . You can then get() to wait for completion and obtain the result.

Can runnable return value?

Return value : Return type of Runnable run() method is void , so it can not return any value. while Callable can return the Future object, which represents the life cycle of a task and provides methods to check if the task has been completed or canceled.

Should I use callable or runnable?

Runnable : If you have a fire and forget task then use Runnable. Put your code inside a Runnable and when the run() method is called, you can perform your task. The calling thread really does not care when you perform your task. Callable : If you are trying to retrieve a value from a task, then use Callable.

How do you handle exceptions in callable?

Utilizing Callable to Throw Exceptions For example, suppose we alter our implementation of Callable to force an exception in our call() method. This will result in an exception being thrown by future. get, which can be handled in the try catch statement surrounding the method call.

Can callable return void?

Generics. We could have either use a random type (e.g. Callable) and return null or no type at all (Callable), but using Void states our intentions clearly.

What does a void function return?

In lieu of a data type, void functions use the keyword “void.” A void function performs a task, and then control returns back to the caller–but, it does not return a value. You may or may not use the return statement, as there is no return value.

What does void method return?

Any method declared void doesn’t return a value. It does not need to contain a return statement, but it may do so.

How do you return a void type?

Related Articles

  1. A void function can do return. We can simply write return statement in a void fun().
  2. A void fun() can return another void function.
  3. A void() can return a void value. A void() cannot return a value that can be used.

Is void a method?

The void keyword allows us to create methods which do not return a value. This method is a void method, which does not return any value. Call to a void method must be a statement i.e. methodRankPoints(255.7);.

What is a return type method?

In computer programming, the return type (or result type) defines and constrains the data type of the value returned from a subroutine or method. In many programming languages (especially statically-typed programming languages such as C, C++, Java) the return type must be explicitly specified when declaring a function.

What is the difference between a void method and a value returning method?

A void method is one that simply performs a task and then terminates. A value – returning method not only performs a task but also sends a value back to the code that called it.

When a method returns a value What does that mean?

In simple terms, it means to return the value to caller of the method… So, in your example, the method getX would return the value of x to the caller, allowing them access to it.

What is a value passed into a method called?

When you declare a parameter to a method or a constructor, you provide a name for that parameter. This name is used within the method body to refer to the passed-in argument. The name of a parameter must be unique in its scope.

What type does the method contains () return?

boolean

Which function returns the method of class?

The getReturnType() method of Method class returns a Class object that represent the return type, declared in method at time of creating the method.

What will be the return type of a method that not returns any value?

What is the return type of a method that does not return any value? Explanation: Return type of a method must be made void if it is not returning any value. 2.

How many values can a method return?

You can return only one value in Java. If needed you can return multiple values using array or an object.

How do you return a value from one method to another in Java?

You have to set the returned value to a variable, otherwise it is lost and you are retrieving the value of “x” in your main method. Do this instead to capture the return value. If you only want to see the returned value and not store it, you can even put the function call inside the System. out.

How do you find the Boolean value?

Boolean Data Values in Java

  1. boolean user = true; So instead of typing int or double or string, you just type boolean (with a lower case “b”).
  2. boolean user = true;
  3. if ( user == true) { System.out.println(“it’s true”);
  4. boolean user = true;
  5. if ( ! user ) {
  6. if ( ! user ) {

How do you compare two Boolean values?

The compare() method of Java Boolean class compares the two Boolean values (x and y) and returns an integer value based on the result of this method….Return Value:

  1. It returns value 0, if x==y.
  2. It returns positive value, if x is true and y is false.
  3. It returns a negative value, if x is false and y is true.

Is 0 True or false Java?

A 0 (zero) is treated as false. Where as in JAVA there is a separate data type boolean for true and false. In C and C++ there is no data type called boolean . That’s why it instead uses 1 and 0 as replacements for true and false values.

How do you return a value from a thread?

How do you return a value from a thread?

get() whenever you need to grab your returned value, the thread is started the very second you give value a value so you don’t ever have to say threadName. start() on it. If you want the value from the calling method, then it should wait for the thread to finish, which makes using threads a bit pointless.

What is thread return?

They both override the call() method of the Callable, and the first returns a Double value, whereas the second one returns an Integer . We create an ExecutorService, using newFixedThreadPool(int nThreads) API method of Executors.

How do you return a value in multithreading?

format(bar) return ‘foo’ + baz from multiprocessing. pool import ThreadPool pool = ThreadPool(processes=1) async_result = pool. apply_async(foo, (‘world’, ‘foo’)) # tuple of args for foo # do some other stuff in the main process return_val = async_result. get() # get the return value from your function.

How do you kill a thread in Python?

There are the various methods by which you can kill a thread in python.

  1. Raising exceptions in a python thread.
  2. Set/Reset stop flag.
  3. Using traces to kill threads.
  4. Using the multiprocessing module to kill threads.
  5. Killing Python thread by setting it as daemon.
  6. Using a hidden function _stop()

What is the return value of pthread_create?

pthread_create() returns zero when the call completes successfully. Any other return value indicates that an error occurred. When any of the following conditions are detected, pthread_create() fails and returns the corresponding value.

Can a runnable return a value?

Return value : Return type of Runnable run() method is void , so it can not return any value. while Callable can return the Future object, which represents the life cycle of a task and provides methods to check if the task has been completed or canceled.

How to get the return value from a thread?

If you really want join () to return the return value of the called function, you can do this with a Thread subclass like the following: from threading import Thread def foo (bar): print ‘hello {0}’.format (bar) return “foo” class ThreadWithReturnValue (Thread): def __init__ (self, group=None, target=None, name=None, args= (), kwargs= {}.

Can a thread return a value without a callback mechanism?

tl;dr a thread cannot return a value (at least not without a callback mechanism). You should reference a thread like an ordinary class and ask for the value. Does this really work? I get The method getValue () is undefined for the type Thread. – pmichna Nov 26 ’13 at 15:07 @pmichna, good spotting. Changing from t.getValue () to foo.getValue ().

How to get return value of thread exit in C + + 11?

Using C++11 threads, one can’t get the return value as thread exit which used to be the case with pthread_exit (…) You need to use C++11 Future<> to get the return value. Future is created using templated argument where the template takes the return value (built in of User Defined types)..

Where do the results of a thread go?

The thread can then store its results in its dedicated slot in that object. For example:

If you really want join () to return the return value of the called function, you can do this with a Thread subclass like the following: from threading import Thread def foo (bar): print ‘hello {0}’.format (bar) return “foo” class ThreadWithReturnValue (Thread): def __init__ (self, group=None, target=None, name=None, args= (), kwargs= {},

tl;dr a thread cannot return a value (at least not without a callback mechanism). You should reference a thread like an ordinary class and ask for the value. Does this really work? I get The method getValue () is undefined for the type Thread. – pmichna Nov 26 ’13 at 15:07 @pmichna, good spotting. Changing from t.getValue () to foo.getValue ().

Using C++11 threads, one can’t get the return value as thread exit which used to be the case with pthread_exit (…) You need to use C++11 Future<> to get the return value. Future is created using templated argument where the template takes the return value (built in of User Defined types)..

The thread can then store its results in its dedicated slot in that object. For example:

Return a value from a thread

  1. We have implemented two classes, RetDouble and RetInt that both implement the Callable, the first using as parameter a Double and the second one using as parameter an Integer .
  2. We create an ExecutorService, using newFixedThreadPool(int nThreads) API method of Executors.

Can a thread return a value in Python?

Threading in Python is simple. Returning values from threads is not possible and, as such, in this example we pass in a globally accessible (to all threads) “results” array with the index of the array in which to store the result once fetched.

How do I return a value from runnable?

Use Callable instead of using Runnable interface. In this example, you will also need to implement the class WordLengthCallable , which implements the Callable interface. Yes, there are workaround. Just use queue and put into it value which you want to return.

How do you end all threads in Python?

Python | Different ways to kill a Thread

  1. Raising exceptions in a python thread.
  2. Set/Reset stop flag.
  3. Using traces to kill threads.
  4. Using the multiprocessing module to kill threads.
  5. Killing Python thread by setting it as daemon.
  6. Using a hidden function _stop()

Which function is used to return a value from the thread back to the main process?

get() # get the return value from your function. Jake’s answer is good, but if you don’t want to use a threadpool (you don’t know how many threads you’ll need, but create them as needed) then a good way to transmit information between threads is the built-in Queue.

Is it possible to return a value to a thread?

Then you can create the thread and retrieve the value (given that the value has been set) tl;dr a thread cannot return a value (at least not without a callback mechanism). You should reference a thread like an ordinary class and ask for the value. Is this answer outdated?

How to get the return value from a thread in Python?

If you really want join () to return the return value of the called function, you can do this with a Thread subclass like the following: That gets a little hairy because of some name mangling, and it accesses “private” data structures that are specific to Thread implementation… but it works.

What happens when pthread _ create ( ) returns?

However, there is no guarantee that this happens. Instead, it is just as likely that pthread_create () returns and the parent thread exits. Once that happens, all data on the parent thread’s stack (including the struct thread_args instance) become invalid. The child thread now has a dangling pointer to potentially corrupted data.

How to retrieve data from a thread function?

In our example, we call the thread function of NumberHelper class from the Main method of Program class. While creating the instance of NumberHelper class we pass the callback function as an argument to that class constructor.

ExecutorService pool = Executors. newFixedThreadPool(2); // creates a pool of threads for the Future to draw from Future value = pool. submit(new Callable() { @Override public Integer call() {return 2;} });

How does thread call method return value?

Threads do not really have return values. However, if you create a delegate, you can invoke it asynchronously via the BeginInvoke method. This will execute the method on a thread pool thread. You can get any return value from such as call via EndInvoke .

What is thread in C#?

Multi-threading is the most useful feature of C# which allows concurrent programming of two or more parts of the program for maximizing the utilization of the CPU. Each part of a program is called Thread. So, in other words, threads are lightweight processes within a process.

What is thread join ()?

Join is a synchronization method that blocks the calling thread (that is, the thread that calls the method) until the thread whose Join method is called has completed. Use this method to ensure that a thread has been terminated. The caller will block indefinitely if the thread does not terminate.

Can a thread return?

tl;dr a thread cannot return a value (at least not without a callback mechanism). You should reference a thread like an ordinary class and ask for the value.

Is callable a thread?

Callable , represents an asynchronous task which can be executed by a separate thread. For instance, it is possible to submit a Callable object to a Java ExecutorService which will then execute it asynchronously.

Can you return a value from a thread?

A thread isn’t a method – you don’t normally “return” a value. However, if you’re trying to fetch a value back from the results of some processing, you have many options, the two main ones being: You can synchronize a shared piece of data, and set it appropriately.

What happens when the thread is running in Java?

When the thread gets a chance to execute, its target run () method will run. It does not return any value. It does not return any value. IllegalThreadStateException – This exception throws if the start () method is called more than one times. System.out.println (“Thread is running…”);

What happens when the thread start ( ) method is called?

The thread moves from New State to Runnable state. When the thread gets a chance to execute, its target run () method will run. It does not return any value. It does not return any value. IllegalThreadStateException – This exception throws if the start () method is called more than one times.

How to run a method on another thread?

There’s a terrific series on threading at Threading in C#. My favorite class, runs any method on another thread with just 2 lines of code. Beware that longFunctionComplete will NOT execute on the same thread as starthework. For methods that take parameters you can always use closures, or expand the class. Simply use the delegate approach.