A java thread is an execution context or a lightweight process. It is a single sequential flow of control within a program. Programmer may use java thread mechanism to execute multiple tasks at the same time
Thread Scheduling
1. New state – After the creations of Thread instance the thread is in this state but before the start() method invocation. At this point, the thread is considered not alive.
2. Runnable (Ready-to-run) state – A thread start its life from Runnable state. A thread first enters runnable state after the invoking of start() method but a thread can return to this state after either running, waiting, sleeping or coming back from blocked state also. On this state a thread is waiting for a turn on the processor
3. Running state – A thread is in running state that means the thread is currently executing. There are several ways to enter in Runnable state but there is only one way to enter in Running state: the scheduler select a thread from runnable pool.
4. Dead state – A thread can be considered dead when its run() method completes. If any thread comes on this state that means it cannot ever run again.
5. Blocked - A thread can enter in this state because of waiting the resources that are hold by another thread.
Thread Scheduling
- When we say that threads are running concurrently, in practice it may not be so. On a computer with single CPU, threads actually run one at a time giving an illusion of concurrency.
- The execution of multiple threads on a single CPU based on some algorithm is called thread scheduling.
- Thread scheduler maintains a pool of all the ready-to-run threads. Based on fixed priority algorithm, it allocates free CPU to one of these threads.
1. New state – After the creations of Thread instance the thread is in this state but before the start() method invocation. At this point, the thread is considered not alive.
2. Runnable (Ready-to-run) state – A thread start its life from Runnable state. A thread first enters runnable state after the invoking of start() method but a thread can return to this state after either running, waiting, sleeping or coming back from blocked state also. On this state a thread is waiting for a turn on the processor
3. Running state – A thread is in running state that means the thread is currently executing. There are several ways to enter in Runnable state but there is only one way to enter in Running state: the scheduler select a thread from runnable pool.
4. Dead state – A thread can be considered dead when its run() method completes. If any thread comes on this state that means it cannot ever run again.
5. Blocked - A thread can enter in this state because of waiting the resources that are hold by another thread.
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