Java – If I synchronized two methods on the same class, can they run simultaneously

javajava-threadsmultithreadingsynchronized

If I synchronized two methods on the same class, can they run simultaneously on the same object? For example:

class A {
    public synchronized void methodA() {
        //method A
    }

    public synchronized void methodB() {
        // method B
    }
}

I know that I can't run methodA() twice on same object in two different threads. same thing in methodB().

But can I run methodB() on different thread while methodA() is still running? (same object)

Best Answer

Both methods lock the same monitor. Therefore, you can't simultaneously execute them on the same object from different threads (one of the two methods will block until the other is finished).

Related Solutions

C++ – Simple example of threading in C++

Create a function that you want the thread to execute, eg:

void task1(std::string msg)
{
    std::cout << "task1 says: " << msg;
}

Now create the thread object that will ultimately invoke the function above like so:

std::thread t1(task1, "Hello");

(You need to #include <thread> to access the std::thread class)

The constructor's arguments are the function the thread will execute, followed by the function's parameters. The thread is automatically started upon construction.

If later on you want to wait for the thread to be done executing the function, call:

t1.join();

(Joining means that the thread who invoked the new thread will wait for the new thread to finish execution, before it will continue its own execution).

The Code

#include <string>
#include <iostream>
#include <thread>

using namespace std;

// The function we want to execute on the new thread.
void task1(string msg)
{
    cout << "task1 says: " << msg;
}

int main()
{
    // Constructs the new thread and runs it. Does not block execution.
    thread t1(task1, "Hello");

    // Do other things...

    // Makes the main thread wait for the new thread to finish execution, therefore blocks its own execution.
    t1.join();
}

More information about std::thread here

On GCC, compile with -std=c++0x -pthread.
This should work for any operating-system, granted your compiler supports this (C++11) feature.

Java synchronized static methods: lock on object or class

Just to add a little detail to Oscar's (pleasingly succinct!) answer, the relevant section on the Java Language Specification is 8.4.3.6, 'synchronized Methods':

A synchronized method acquires a monitor (§17.1) before it executes. For a class (static) method, the monitor associated with the Class object for the method's class is used. For an instance method, the monitor associated with this (the object for which the method was invoked) is used.

Best Answer

Related Solutions

C++ – Simple example of threading in C++

The Code

Java synchronized static methods: lock on object or class

Related Topic