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    <p>While you are using synchronized(this) you are using the class instance as a lock itself. This means that while lock is acquired by thread 1 the thread 2 should wait</p> <p>Suppose the following code</p> <pre><code>public void method1() { do something ... synchronized(this) { a ++; } ................ } public void method2() { do something ... synchronized(this) { b ++; } ................ } </code></pre> <p>Method 1 modifying the variable <em>a</em> and method 2 modifying the variable <em>b</em>, the concurrent modification of the same variable by two threads should be avoided and it is. BUT while <em>thread1</em> modifying <em>a</em> and <em>thread2</em> modifying <em>b</em> it can be performed without any race condition.</p> <p>Unfortunately, the above code will not allow this since we are using the same reference for a lock; This means that threads even if they are not in a race condition should wait and obviously the code sacrifices concurrency of the program.</p> <p>The solution is to use <em>2</em> different locks for <em>two</em> different variables.</p> <pre><code> class Test { private Object lockA = new Object(); private Object lockB = new Object(); public void method1() { do something ... synchronized(lockA) { a ++; } ................ } public void method2() { do something ... synchronized(lockB) { b ++; } ................ } </code></pre> <p>The above example uses more fine grained locks (2 locks instead one (<em>lockA</em> and <em>lockB</em> for variables <em>a</em> and <em>b</em> respectively) and as a result allows better concurrency, on the other hand it became more complex than the first example ...</p>
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    1. POAvoid synchronized(this) in Java?
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    1. USArtem Russakovskii
    1. USAndreas Bakurov
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    1. COThis is very dangerous. You've now introduced a client-side (user's of this class) lock ordering requirement. If two threads are calling method1() and method2() in a different order, they are likely to deadlock, but the user of this class has no idea that this is the case.
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      1. USdaveb
    2. COI can not see a deadlock situation here...
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      1. USMalkocoglu
    3. COGranularity not provided by "synchronized(this)" is out of the scope of my question. And shouldn't your lock fields be final?
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      1. USeljenso
 

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