Java Community | Help. Code. Learn.•2y ago

question about multithreading

Hello. I'm using multithreading with spark and have a question. I'm using Scala but shouldn't matter.

// Java code for thread creation by implementing
// the Runnable Interface
class MultithreadingDemo implements Runnable {
    public void run()
    {
        try {
            // Displaying the thread that is running
            Foo(dataframe1)
                        Foo(dataframe2)
                        Foo(dataframe3)
        }
        catch (Exception e) {
            // Throwing an exception
            System.out.println("Exception is caught");
        }
    }
}

// Main Class
class Multithread {
    public static void main(String[] args)
    {
        int n = 3; // Number of threads
        for (int i = 0; i < n; i++) {
            Thread object
                = new Thread(new MultithreadingDemo());
            object.start();
        }
    }
}

// Java code for thread creation by implementing
// the Runnable Interface
class MultithreadingDemo implements Runnable {
    public void run()
    {
        try {
            // Displaying the thread that is running
            Foo(dataframe1)
                        Foo(dataframe2)
                        Foo(dataframe3)
        }
        catch (Exception e) {
            // Throwing an exception
            System.out.println("Exception is caught");
        }
    }
}

// Main Class
class Multithread {
    public static void main(String[] args)
    {
        int n = 3; // Number of threads
        for (int i = 0; i < n; i++) {
            Thread object
                = new Thread(new MultithreadingDemo());
            object.start();
        }
    }
}

above is simple multithreading from geeksforgeeks.org. I just changed n to 3 because that's what i'm using in Scala and put custom function in run() as an example. I was working with spark and saw unexpected behavior. I have a function called Foo that takes in dataframe and return dataframe. Inside Foo, modifications and optimizations are applied to dataframe. when I run the code I thought I would be assigning spark job to each thread, therefore I would be able to run 3 jobs that require dataframes at the same time. But I just tried to print something inside that Foo and it printed out 7 times. I was expecting 3 times. What's causing it to print out 7 times rather than 3 times? Am I misunderstanding something about multithreading?

3 Replies

JavaBot•2y ago

⌛ This post has been reserved for your question.

Hey @VaygrEmpire! Please use /close or the Close Post button above when you're finished. Please remember to follow the help guidelines. This post will be automatically closed after 300 minutes of inactivity.

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VaygrEmpireOP•2y ago

figured

JavaBot•2y ago

Post Closed

This post has been closed by <@205489120984825857> for the following reason:

figured out myself

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question about multithreading

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