When do I need to use AtomicBoolean in Java

Question

How I can use AtomicBoolean and what is that class for

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Excerpt from the package description     Package java util concurrent atomic description  A small toolkit of classes that support lock-free thread-safe programming on single variables             The specifications of these methods enable implementations to employ efficient machine-level atomic instructions that are available on contemporary processors             Instances of classes AtomicBoolean  AtomicInteger  AtomicLong  and AtomicReference each provide access and updates to a single variable of the corresponding type            The memory effects for accesses and updates of atomics generally follow the rules for volatiles          get has the memory effects of reading a volatile variable    set has the memory effects of writing  assigning  a volatile variable    weakCompareAndSet atomically reads and conditionally writes a variable  is ordered with respect to other memory operations on that variable  but otherwise acts as an ordinary non-volatile memory operation    compareAndSet and all other read-and-update operations such as getAndIncrement have the memory effects of both reading and writing volatile variables

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There are two main reasons why you can use an atomic boolean   First its mutable  you can pass it in as a reference and change the value that is a associated to the boolean itself  for example   public final class MyThreadSafeClass       private AtomicBoolean myBoolean   new AtomicBoolean false       private SomeThreadSafeObject someObject   new SomeThreadSafeObject         public boolean doSomething             someObject doSomeWork myBoolean            return myBoolean get      will return true           and in the someObject class  public final class SomeThreadSafeObject      public void doSomeWork AtomicBoolean b           b set true             More importantly though  its thread safe and can indicate to developers maintaining the class  that this variable is expected to be modified and read from multiple threads   If you do not use an AtomicBoolean you must synchronize the boolean variable you are using by declaring it volatile or synchronizing around the read and write of the field

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Here is the notes  from Brian Goetz book  I made  that might be of help to you  AtomicXXX classes   provide Non-blocking Compare-And-Swap implementation Takes advantage of the support provide by hardware  the CMPXCHG instruction on Intel  When lots of threads are running through your code that uses these atomic concurrency API  they will scale much better than code which uses Object level monitors synchronization  Since  Java s synchronization mechanisms makes code wait  when there are lots of threads running through your critical sections  a substantial amount of CPU time is spent in managing the synchronization mechanism itself  waiting  notifying  etc   Since the new API uses hardware level constructs  atomic variables  and wait and lock free algorithms to implement thread-safety  a lot more of CPU time is spent  doing stuff  rather than in managing synchronization  not only offer better throughput  but they also provide greater resistance to liveness problems such as deadlock and priority inversion

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The AtomicBoolean class gives you a boolean value that you can update atomically  Use it when you have multiple threads accessing a boolean variable   The java util concurrent atomic package overview gives you a good high-level description of what the classes in this package do and when to use them  I d also recommend the book Java Concurrency in Practice by Brian Goetz

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When multiple threads need to check and change the boolean  For example   if   initialized       initialize       initialized   true      This is not thread-safe  You can fix it by using AtomicBoolean   if  atomicInitialized compareAndSet false  true         initialize

[java] When do I need to use AtomicBoolean in Java?

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