Wait until boolean value changes it state

Question

I have a thread which wait for a boolean value to change like this   while  value      Thread sleep 1000       Do some work after change of the value   This is not my prefered way to do this  cause of massive CPU consumption   Is there any way to block the Thread  until the boolean value changes it state

User · Answer

public Boolean test   throws InterruptedException       BlockingQueue lt Boolean gt  booleanHolder   new LinkedBlockingQueue lt  gt         new Thread    - gt            try               TimeUnit SECONDS sleep 2               booleanHolder put true             catch  InterruptedException e                e printStackTrace                     start        return booleanHolder poll 4  TimeUnit SECONDS

User · Answer

I prefer to use mutex mechanism in such cases  but if you really want to use boolean  then you should declare it as volatile  to provide the change visibility across threads  and just run the body-less cycle with that boolean as a condition            some class  volatile boolean someBoolean    Thread someThread   new Thread           Override      public void run               some actions         while   someBoolean     wait for condition            some actions

User · Answer

Ok maybe this one should solve your problem  Note that each time you make a change you call the change   method that releases the wait   Integer any   new Integer 0    public synchronized boolean waitTillChange         any wait        return true     public synchronized void change         any notify

User · Answer

How about wait-notify   private Boolean bool   true  private final Object lock   new Object     private Boolean getChange      synchronized lock       while  bool          bool wait                 return bool    public void setChange       synchronized lock          bool   false         bool notify

User · Answer

You need a mechanism which avoids busy-waiting  The old wait notify mechanism is fraught with pitfalls so prefer something from the java util concurrent library  for example the CountDownLatch   public final CountDownLatch latch   new CountDownLatch 1    public void run        latch await              And at the other side call  yourRunnableObj latch countDown      However  starting a thread to do nothing but wait until it is needed is still not the best way to go  You could also employ an ExecutorService to which you submit as a task the work  which must be done when the condition is met

User · Answer

This is not my prefered way to do this  cause of massive CPU consumption    If that is actually your working code  then just keep it like that  Checking a boolean once a second causes NO measurable CPU load  None whatsoever   The real problem is that the thread that checks the value may not see a change that has happened for an arbitrarily long time due to caching  To ensure that the value is always synchronized between threads  you need to put the volatile keyword in the variable definition  i e   private volatile boolean value    Note that putting the access in a synchronized block  such as when using the notification-based solution described in other answers  will have the same effect

[java] Wait until boolean value changes it state

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