Why wait should be called in loop?
When you check the waiting condition in the loop you ensure that thread will test the condition after it wakes up to see if the condition still holds or not. If you are not familiar with notify and notifyAll method, you can further see The Complete Java Masterclass to learn more.
Why wait and notify should be called from synchronized block?
The wait() is called, so that the thread can wait for some condition to occur when this wait() call happens, the thread is forced to give up its lock. Thread needs to own the lock first. Hence the need to call it inside a synchronized method/block.
Can we use wait and notify without synchronized?
If you need to call wait(), notify(), or notifyAll() from within a non-synchronized method, then you must first obtain a lock on the object’s monitor. If you don’t, an exception will be generated when an attempt is made to call the method in question.
What happens when a thread executes wait () method on an object without owning the object’s lock?
Beside above, what happens when a thread executes wait () method on an object without owning the object’s lock? The wait(), notify(), and notifyAll() methods should be called for an object only when the current thread has already locked the object’s lock. Note also that wait() forces the thread to release its lock.
Does wait method release lock?
When thread calls wait it releases the current object lock (it keeps all locks from other objects) and than goes to WAITING state. So to summarize, thread acquires the lock when it enters synchronized method or when it reenters the synchronized method after the wait.
Does notify Release lock?
The notifying thread only releases the lock once it completes the execution of its synchronized code on the lock object it is going to release. If the execution of the synchronized code is completed or there are no statements after notify(), then the thread releases the lock for waken up threads from waiting state.
What if Notify is called before wait?
Therefore, if a thread calls notify() before the thread to signal has called wait(), the signal will be missed by the waiting thread. This may or may not be a problem, but in some cases this may result in the waiting thread waiting forever, never waking up, because the signal to wake up was missed.
Can we override wait () or notify () methods?
Because of this, all Java classes inherit methods from Object . Object declares three versions of the wait method, as well as the methods notify , notifyAll and getClass . These methods all are final and cannot be overridden.
What is the difference between wait () notify () and notifyAll ()?
The wait() method causes the current thread to wait until another thread invokes the notify() or notifyAll() methods for that object. The notify() method wakes up a single thread that is waiting on that object’s monitor. The notifyAll() method wakes up all threads that are waiting on that object’s monitor.
What is notify () in Java?
notify() wakes up a single thread that is waiting on this object’s monitor. By executing a synchronized instance method of that object. By executing the body of a synchronized statement that synchronizes on the object. For objects of type Class, by executing a synchronized static method of that class.
What is wait () in Java?
wait() causes current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object. The thread then waits until it can re-obtain ownership of the monitor and resumes execution. This method should only be called by a thread that is the owner of this object’s monitor.
What happens if you don’t call wait and notify from synchronized block?
Why do we need synchronization?
The need for synchronization originates when processes need to execute concurrently. The main purpose of synchronization is the sharing of resources without interference using mutual exclusion. The other purpose is the coordination of the process interactions in an operating system.
What happens if sleep () and wait () executes in synchronized block?
The major difference is that wait() releases the lock or monitor while sleep() doesn’t releases the lock or monitor while waiting. wait() is used for inter-thread communication while sleep() is used to introduce pause on execution, generally.
Is it important to acquire object lock before calling wait () notify () and notifyAll ()?
If no threads are waiting in the waiting queue, then notify() and notifyAll() have no effect. Before calling the notify() or notifyAll() method of an object, a thread must own the lock of the object. Hence it must be in one of the object’s synchronizedmethods or synchronized block.
What happens if we call start () method in thread on a twice?
No. After starting a thread, it can never be started again. If you does so, an IllegalThreadStateException is thrown. In such case, thread will run once but for second time, it will throw exception.
When a thread is waiting as a result of wait () it releases its lock?
When a thread calls Wait , it releases the lock on the object and enters the object’s waiting queue. The next thread in the object’s ready queue (if there is one) acquires the lock and has exclusive use of the object.
Why wait notify and notifyAll are not inside thread class?
Answer to your first question is As every object in java has only one lock(monitor) and wait(),notify(),notifyAll() are used for monitor sharing thats why they are part of Object class rather than Thread class. wait – wait method tells the current thread to give up monitor and go to sleep.
Which class defines wait () notify () and Notifyall () methods?
Hence, wait() and notify() methods are defined in Object class rather than Thread class. If wait() and notify() were on the Thread instead then each thread would have to know the status of every other thread and there is no way to know thread1 that thread2 was waiting for any resource to access.
What is object locking in Java?
Object level locking means you want to synchronize non static method or block so that it can be accessed by only one thread at a time for that instance. It is used if you want to protect non static data. You can achieve Object level locking by following.