Why must wait always be in 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. To give up something, you need to own it first. Thread needs to own the lock first. Hence the need to call it inside a synchronized method/block.
Why wait () and notify () must be inside a synchronized method or block?
There are few points we should be aware of before going into the reasons for why wait (), notify () and notifyAll () must be called inside a synchronized method or block. Every object created in Java has one associated monitor (mutually exclusive lock). Only one thread can own a monitor at any given time.
Why do I need to synchronize with wait ()?
This basically has to do with the hardware architecture (i.e. RAM and caches ). If you don't use synchronized together with wait () or notify (), another thread could enter the same block instead of waiting for the monitor to enter it.
When a thread is awakened it cannot exit its synchronized block?
Once a thread is awakened it cannot exit the wait () call until the thread calling notify () has left its synchronized block. What is difference between lock and synchronization in Java?
What happens if you lock an object in synchronized block?
If you choose the locked object carefully, synchronized blocks will lead to less contention, because the whole object/class is not blocked. What happens if sleep () and wait () executes in synchronized block? sleep () sends the current thread into the “Not Runnable” state for some amount of time.
Why wait notify notifyAll must be called inside a synchronized method block?
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.
Can I use wait 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.
Why should wait () always be called inside a loop?
To guarantee liveness, programs must test the while loop condition before invoking the wait() method. This early test checks whether another thread has already satisfied the condition predicate and sent a notification. Invoking the wait() method after the notification has been sent results in indefinite blocking.
Is it necessary to call wait and notify from synchronized method?
Explanation: Option A is correct because the notifyAll() method (along with wait() and notify()) must always be called from within a synchronized context. Option B is incorrect because to call wait(), the thread must own the lock on the object that wait() is being invoked on, not the other way around.
Does wait () Release lock from synchronized block?
The wait function doesn't release "all locks", but it does release the lock associated with the object on which wait is invoked.
Why wait notify called from synchronized?
Calling notify() or notifyAll() methods issues a notification to a single or multiple threads that a condition has changed and once the notification thread leaves the synchronized block, all the threads which are waiting for fight for object lock on which they are waiting and lucky thread returns from wait() method ...
Why wait () notify () and notifyAll () methods have to be called from synchronized method or block illustrate with an example?
wait method tells the current thread (thread which is executing code inside a synchronized method or block) to give up monitor and go to waiting state. notify method wakes up a single thread that is waiting on this object's monitor. notifyAll method wakes up all the threads that called wait() on the same object.
Why wait notify and notifyAll are in object 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. Hence, notify, wait, notifyAll methods are defined in object class in Java.
Why do we use synchronized block in Java?
A Synchronized block is a piece of code that can be used to perform synchronization on any specific resource of the method. A Synchronized block is used to lock an object for any shared resource and the scope of a synchronized block is smaller than the synchronized method.
Can we override wait () or notify () methods?
Can we override wait() or notify() methods? Ans. wait and notify are declared final in object class and hence cannot be overridden.
What happens if exception is thrown in synchronized block?
When an exception occurs from within a synchronized code block, then JVM smartly releases all the locks acquired by the current thread and will start unwinding the execution stack, till the exception is handled using catch block, otherwise killing the thread.
What is the purpose of the wait () notify () and notifyAll () methods?
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.
Can we override wait () or notify () methods?
Can we override wait() or notify() methods? Ans. wait and notify are declared final in object class and hence cannot be overridden.
Why wait () notify () and notifyAll () methods have to be called from a synchronized method or block?
The wait(), notify(), and notifyAll() methods should be called for an object only when the current thread has already locked the object's lock. This point sometimes goes unnoticed because programmers are used to calling these methods from within synchronized methods or blocks. Otherwise, you will get "java.
What is the use of wait method in Java?
The wait() Method Simply put, calling wait() forces the current thread to wait until some other thread invokes notify() or notifyAll() on the same object. For this, the current thread must own the object's monitor.
What happens if exception is thrown in synchronized block?
When an exception occurs from within a synchronized code block, then JVM smartly releases all the locks acquired by the current thread and will start unwinding the execution stack, till the exception is handled using catch block, otherwise killing the thread.
What is a synchronized monitor in Java?
For achieving synchronization in Java this monitor is used. When any thread enters a synchronized method/block it acquires the lock on the specified object. When any thread acquires a lock it is said to have entered the monitor. All other threads which need to execute the same shared piece of code (locked monitor) will be suspended until the thread which initially acquired the lock releases it.
What happens when a thread acquires a lock?
When any thread acquires a lock it is said to have entered the monitor. All other threads which need to execute the same shared piece of code (locked monitor) will be suspended until the thread which initially acquired the lock releases it. wait method tells the current thread (thread which is executing code inside a synchronized method or block) ...
When is an object's lock acquired?
Object's lock is acquired by a thread only when it is executing in a synchronized context. So it makes sense to use wait () method, which asks thread to release the lock, only in synchronized context. Same way; when object's notify () or notifyAll () method is called, single thread (in case of notify) or all of the threads (in case of notifyAll), ...
Can a method be executed by more than one thread?
Any method or a block of code, if not qualified with the keyword synchronized can be executed by more than one thread at any given time as object's monitor (lock) is not in the picture. Where as when a method is synchronized (or there is a synchronized block) only a single thread who has acquired the object's monitor can access the code.
