Thread state

Threads can exist in five distinct states: running, not-running, runnable, starting, and ended. When we create a thread, we have, typically, not allocated any resources towards this thread as of yet. It exists in no state, as it hasn't been initialized, and it can only be started or stopped. Let's take a quick look at these five states:

• New Thread: In the New Thread state, our thread hasn't started, and it hasn't been allocated resources. It is merely an instance of an object.
• Runnable: This is the state when the thread is waiting to run, it has all the resources it needs in order to proceed, and the only thing holding it back is the task scheduler having not scheduled it to run.
• Running: In this state, the thread makes progress--it executes whatever task it's meant to and has been chosen by the task scheduler to run.
  From this state, our thread can go into either a dead state if we chose to kill, it or it could go into a not-running state.
• Not-running: This is when the thread has been paused in some way. This could be caused by a number of reasons such as when waiting for the response of a long running I/O request. Or it could be deliberately blocked until another thread has completed its execution.
• Dead: A thread can reach this state through one of two ways. It can, much like us, die of natural causes or be killed unnaturally. The latter poses a significant risk to the murderer, but we'll go into these risks in detail in the ending a thread section of this chapter.