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    <p>This is not how you get a deadlock. Actually this code seems pretty safe :-) Only one thread enters sum/sub at a time because you are using synchronized which synchronizes on "this". There is only one "this" so both threads try to acquire the same lock.</p> <p>Deadlock occurs, for instance, when Thread1 has one lock, Thread2 has second lock and then Thread1 would like to acquire Thread2's lock while still holding it's lock and Thread2 would like to acquire Thread1's lock while still holding it's lock.</p> <p>What you could do is:</p> <p>a) add 2 objects for locking in "threadexample" class (btw classes by convention should start with uppercase):</p> <pre><code>private final Object sumLock = new Object(); private final Object subLock = new Object(); </code></pre> <p>b) drop the "synchronized" keyword in both sum/sub methods and instead use the synchronized() {} block in each of them. Sum would be synchronized(sumLock) { /* sum's body goes here <em>/ } and sub would be synchronized(subLock) { /</em> sub's body goes here */}.</p> <p>In this case Thread1 would go into sum(), acquire the sumLock and wait. Thread2 would go into sub(), acquire the subLock() and wait. Thread1 would wake up, go into sub() and try to acquire subLock but it's being held by Thread2 so it wait's until Thread2 releases it. In that time Thread2 wakes up, goes into sum() and tries to acquire sumLock which is held by Thread1 so Thread2 waits for Thread1 to release it.</p> <p>Neither thread will go forward as each one of them is waiting for the other - you have a deadlock.</p> <p>@Edit: yes you have only 1 instance of "threadexample" and both Thread1 and Thread2 are fighting for the lock but when one of them acquires the lock it will release it after executing sum/sub or sub/sum. For instance let's say Thread1 is first and starts executing sum(). It has the lock. In that case Thread2 will not go into sub() as it is protected by the same lock as Thread1. Thread1 will do sum(), then sub() and then it will release the lock --> Thread2 will go into sub() etc.</p>
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    1. POImplementing deadlock condition
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    1. USMateusz Dymczyk
    1. USMateusz Dymczyk
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    1. COSorry but I do not understand. This may be because I am new to threading. As per my understanding, I have made only one object of class threadexample. and Thread1 and Thread2 are competing for acquiring lock on sum() and sub().
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      1. USBhaskar
 

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