Deadlock Avoidance
Although it is not possible to avoid the deadlock condition, we can prevent it by using the following methods:
-
Avoid nested locks: A deadlock in Java mainly happens when we provide multiple locks to multiple threads. So avoid giving a lock to multiple threads if we have already given to one.
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Avoid unnecessary locks: We should always try to avoid providing unnecessary locks to threads. We must use locks only for those members on which it is required.
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Using Thread.join() Method: There are chances of a deadlock condition when one thread waits for another to complete the execution. If a deadlock condition occurs, we can use thread.join() with the maximum time the execution will take.
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Lock Time-out: We can prevent a deadlock by using the time-out condition if a thread does not acquire a lock within a specific time.
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Use Lock Ordering: In this method, each lock has a numeric value, and if we acquire the locks with a lower numeric value before those with a higher numeric value, we can avoid a deadlock situation.
Here is an example for a better understanding.
Example
class AvoidDeadlock
{
public static void main(String[] args) throws InterruptedException
{
final String objt1="Object1";
final String objt2="Object2";
final String objt3="Object3";
Thread th1=new Thread(new SynchroniseThread(objt1, objt2), "th1");
Thread th2=new Thread(new SynchroniseThread(objt2, objt3), "th2");
th1.start();
Thread.sleep(1000);
th2.start();
Thread.sleep(1000);
}
}
class SynchroniseThread implements Runnable
{
private Object objt1;
private Object objt2;
public SynchroniseThread(Object ob1, Object ob2)
{
this.objt1=ob1;
this.objt2=ob2;
}
@Override
public void run()
{
String thread_name=Thread.currentThread().getName();
System.out.println(thread_name+" acquiring the lock on "+objt1);
synchronized (objt1)
{
System.out.println(thread_name+" acquired the lock on "+objt1);
try
{
Thread.sleep(2000);
}
catch(InterruptedException e)
{
e.printStackTrace();
}
}
System.out.println(thread_name+" released the lock on "+objt1);
System.out.println(thread_name+" acquiring the lock on "+objt2);
synchronized (objt2)
{
System.out.println(thread_name+" acquired the lock on "+objt2);
try
{
Thread.sleep(2000);
}
catch(InterruptedException e)
{
e.printStackTrace();
}
}
System.out.println(thread_name+" released the lock on "+objt2);
}
}
Output
th1 acquiring the lock on Object1
th1 acquired the lock on Object1
th2 acquiring the lock on Object2
th2 acquired the lock on Object2
th1 released the lock on Object1
th1 acquiring the lock on Object2
th2 released the lock on Object2
th1 acquired the lock on Object2
th2 acquiring the lock on Object3
th2 acquired the lock on Object3
th1 released the lock on Object2
th2 released the lock on Object3
Try it by yourself on java online compiler.
Frequently Asked Questions
How do you detect deadlock in Java?
We can detect if a deadlock condition has occurred in Java by running the program in CMD. The command depends upon the OS type and Java version. Using the command, we can collect the thread dumps to analyze the root cause of the deadlock situation. If we are running Java 8 on windows, a command would be jcmd $PID Thread.print.
What is Deadlock in Java?
Deadlock in Java is a programming situation that occurs when two or more threads wait for each other to release the resource(lock) they need and get stuck for an infinite time.
What is multi-threading in Java?
Multi-threading is a Java feature that allows simultaneous execution of multiple threads for maximum CPU utilization. A thread is a lightweight sub-process, the smallest unit of processing.
Conclusion
In this article, we have extensively discussed Deadlock Prevention and Avoidance in the java programming language. We also discussed How to avoid deadlock in Java with the help of an example.
Recommended Readings:
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