deadlock

Hi!

// An example of deadlock. 
class A { 
    synchronized void foo(B b) { 
        String name = Thread.currentThread().getName(); 
        System.out.println(name + " entered A.foo"); 
        try { 
            Thread.sleep(1000); 
        } catch(Exception e) { 
            System.out.println("A Interrupted"); 
        } 
        System.out.println(name + " trying to call B.last()"); 
        b.last(); 
    }

synchronized void last() { 
        System.out.println("Inside A.last"); 
    } 
}

class B { 
    synchronized void bar(A a) { 
        String name = Thread.currentThread().getName(); 
        System.out.println(name + " entered B.bar"); 
        try { 
            Thread.sleep(1000); 
        } catch(Exception e) { 
            System.out.println("B Interrupted"); 
        }
        System.out.println(name + " trying to call A.last()"); 
        a.last(); 
    }

synchronized void last() { 
        System.out.println("Inside A.last"); 
    } 
}

class Deadlock implements Runnable { 
    A a = new A(); 
    B b = new B(); 
    Deadlock() { 
        Thread.currentThread().setName("MainThread"); 
        Thread t = new Thread(this, "RacingThread"); 
        t.start(); 
        a.foo(b); // get lock on a in this thread. 
        System.out.println("Back in main thread"); 
    }
 
    public void run() { 
        b.bar(a); // get lock on b in other thread. 
        System.out.println("Back in other thread"); 
    }

public static void main(String args[]) { 
        new Deadlock(); 
    } 
}

http://www.java-samples.com/showtutorial.php?tutorialid=307

This is an example of deadlock, But I can't understand where is the deadlock in that code?

The deadlock happened when two thread want to access one resource, But I don't such thing in that coe

Please guide me

[HENRY: Formatted Code]

abalfazl hossein wrote:
http://www.java-samples.com/showtutorial.php?tutorialid=307

This is an example of deadlock, But I can't understand where is the deadlock in that code?

The deadlock happened when two thread want to access one resource, But I don't such thing in that coe

I think your definition of deadlock is incorrect. There are actually many ways to deadlock, and the example is defining it as and showing as... A deadlock can occur when two threads are trying to grab two different locks. They each grab one of the locks, and then wait for the other lock. In this case, the deadlock is occuring because neither can grab the other lock because it is owned by the other thread -- and neither will release the lock that they did grab because they are both in a wait state waiting for the other lock. This condition can't be resolved, hence, deadlock.

Henry

OK, As you define the deadlock. Now Please tell me how deadlock happened in that code?

abalfazl hossein wrote:OK, As you define the deadlock. Now Please tell me how deadlock happened in that code?

You can't see it? It is pretty clear.... plus the code is loaded with print statements so that you can follow it.

Try it. Run the code.... And if you still don't see it, describe what you do see, and we'll give you some hints on where you went wrong.

Henry

There is only one lock fro every object.

Then when Mainthread takes lock of class A,Racing thread couldn't take lock of class A.

You can see a full thread and monitor cache dump by pressing CTRL-BREAK on a PC (or CTRL-\\ on Solaris).

http://www.java-samples.com/showtutorial.php?tutorialid=307

I use Netbeans,I press CTRL-BREAK while I run that program , but I didn't see anything.

I search and find about Netbeans:

http://profiler.netbeans.org/

But I didn't see any link to download this add on....

and don't find that on Netbeans....

I also try SendSignal in cmd....But unlucky....I don't know how to find the ID of process that is belongs to program that I run .....

I want to see thread dump. What is the simplest way?

The path to a secure application ,IBM

e. Race conditions
Two processes might share control or data. Race conditions is
the term applied to compromising this sharing, which typically
results from synchronization errors, when the potential exists
for process conflicts, and a resulting vulnerability. A typical
exploit interrupts a pair of sequential calls that are meant to be
performed automatically without interruption by another
thread or process on the machine with a third process.

One example is the combined checking of access rights to a
file, followed by a subsequent call to write or read that file. By
interrupting the process between the two calls, an attacker can
rewrite or modify the file because this behavior is expected.
The attacker can place inappropriate information into a file,
or perhaps access an inappropriate file

May someone explain more about the example?