Thread

26 Jun 2022 . os .

Process VS Thread

  • Process: The smallest unit of resource allocation. Static and used to allocate resources.
  • Thread: The smallest unit of CPU scheduling. Dynamic and used to execute instructions.
Process Thread
It is a computer program that is under execution. It is the component or entity of the process that is the smallest execution unit.
It can be divided into multiple threads. It can’t be further subdivided.
It has its own memory space and run-in separate memory space. It uses the memory of the process it belongs to and run-in shared memory space..
These are heavy-weight operators. These are light-weight operators.
It requires more resources. It requires fewer resources.

State

New

A new thread is created.

Runnable

A thread is running or is ready to run(waiting for CPU).

Blocked

A thread blocked waits for a monitor lock to enter synchronized block/method.


Waiting

A thread is waiting for another thread to perform a particular action.

Timed Waiting

A thread calls a method with timeout.

Terminated

A thread has completed execution.

Context Switch

  1. Thread gives up the CPU, such as calling sleep(), wait().
  2. Time slices run out. The operating system wants to prevent a thread or a process from occupying the CPU for a long time and causing other threads or processes starvation.
  3. A system interrupt, such as requesting an IO, and the thread is blocked.

Runnable VS Callable

  • Code

      public interface Runnable {
      public abstract void run();
  }

      public interface Callable<V> {
      V call() throws Exception;
  }

execute() VS submit()

  • The execute() method is used to commit tasks that do not require return values, so it is impossible to judge whether the task has been executed successfully by the thread pool.
  • The submit() method is used to submit tasks that require a return value. The thread pool will return an object of Future type, through which you can judge whether the task is executed successfully. The return value can be obtained through the get() method of Future.

Important Methods

  • Thread.yeild()
    1. Release lock
    2. Running ⇒ Runnable
  • Thread.sleep()
    1. Release lock
    2. Running ⇒ Timed Waiting
  • Thread.join()
    1. t2.join()
    2. t1 releases Object lock
    3. t1 Running ⇒ Waiting
    4. t2 finished
    5. t1 Waiting ⇒ Running

    Bottom logic is wait().

  • Object.wait()
    1. Release locks
    2. Running ⇒ Waiting
    3. Wait for another thread to call Object.notify() or Object.notifyAll()
    4. Waiting ⇒ Blocked
    5. Wait to enter synchronized block
    6. Receive the monitor lock
    7. Blocked ⇒ Running