Lesson 4 - Multithreading in Java - Inter-thread Communication
In the previous lesson, Multithreading in Java - Synchronization in practice, we tried thread synchronization for the first time. This is realized by means of monitors. Today, we're going to show that the capabilities of these monitors definitely don't end with synchronization.
Inter-thread Communication
Java offers three methods related to inter-thread communication. These are
the wait()
, notify()
, and notifyAll()
methods. You've already encountered them for sure because they are defined by
the Object
class and therefore each object contains them. At first
glance, it may seem a little confusing - why are these methods part of every
object, why the aren't defined simply by the Thread
class? And how
can we use such methods? You may have already noticed that using monitors
divides our threads into groups according to the monitors they use. The threads
in these groups can then interact with each other via the shared monitor. And
since we know that any object can be a monitor, it was necessary for every
object to contain these controlling methods.
To be able to call these methods on the monitor successfully, we need to own the monitor at the moment (I mean that our thread has to own it). And when are we sure we own a monitor? Well, in the
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We'll explain inter-threaded communication using the wait(), notify() and notifyAll() methods. The examples will also show deadlock and spurious wakeup.
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