Previously we have discussed about
Java Thread Model
The Java run-time system depends on threads for many things, and all the class libraries are designed with multithreading.
Single-threaded systems use an approach called an event loop with polling.
In this model, a single thread of control runs in an infinite loop, polling a single event queue to decide what to do next. Once this polling mechanism returns with, say, a signal that a network file is ready to be read, then the event loop dispatches control to the appropriate
event handler. Until this event handler returns, nothing else can happen in the program. This wastes CPU time. It can also result in one part of a program dominating the system and preventing any other events from being processed. In general, in a single-threaded environment, when a thread blocks (that is, suspends execution) because it is waiting for some resource, the entire program stops running.
The benefit of Java’s multithreading is that the main loop/polling mechanism is eliminated. One thread can pause without stopping other parts of your program. For example, the idle time created when a thread reads data from a network or waits for user input can be utilized elsewhere.
Multithreading allows animation loops to sleep for a second between each frame without causing the whole system to pause. When a thread blocks in a Java program, only the single thread that is blocked pauses. All other threads continue to run.
It is important to understand that Java’s multithreading features work in both types of systems. In a singlecore system, concurrently executing threads share the CPU, with each thread receiving a slice of CPU time.Therefore, in a single-core system, two or more threads do not actually run at the same time, but idle CPU time is utilized.
However, in multi-core systems, it is possible for two or more threads to actually execute simultaneously.
Threads exist in several states. Here is a general description. A thread can be running. It can be ready to run as soon as it gets CPU time. A running thread can be suspended, which temporarily halts its activity. A suspended thread can then be resumed, allowing it to pick up where it left off. A thread can be blocked when waiting for a resource. At any time, a thread can be terminated, which halts its execution immediately. Once terminated, a thread cannot be resumed.
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