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Multiprogramming

HadjshellAbout 1 minNoteLanguageJava
  • Multiprogramming

    • Running more than one programs on a single computer

Go read the Concurrency chapter of Thinking in Java

  • By multiprogramming CPU's idle time is minimised
  • A Thread of execution is the smallest sequence of programmed instructions that can be managed independently
  • In many cases, a thread is a component of a process
  • Useful for web server, GUI, animation, etc.

How to Implement Multithreading

  1. extends or implements or lambda expression

    • Depends on whether the subclass is inherited a superclass or not
    • Thread class
    • Runnable interface

  2. Overriding the run() method

    • run() is the starting point of a thread

  3. Start the thread

    • If implements Runnable, Thread t = new Thread(new Object()); t.start();
    • If extends Thread, o.start();

Thread class

  • States of Thread

    • thread-states
      thread-states

  • Thread priority

    • Scheduler in JVM maintains a thread ready queue
    • The exact behaviour depends on the JVM

  • Constructors

    • Thread()
    • Thread(Runnable r)
    • Thread(Runnable r, String name)
    • Thread(ThreadGroup g, String name)

  • Getter and setter

    • long getId()
    • String getName()
    • int getPriority()
      • Default priority of a thread (NORM_PRIORITY) in Java is 5; MIN_PRIORITY is 1 and MAX_PRIORITY is 10
    • ThreadState getState()
    • ThreadGroup getThreadGroup()
    • void setName(String name)
    • void setPriority(int p)
    • void setDaemon(boolean b)
      • A daemon thread is the background thread with least priority
      • An example: garbage collector

  • Enquiry methods

    • boolean isAlive()
    • boolean isDaemon()
    • boolean isInterrupted()

  • Instance methods

    • void inerrupt()

    • void join()

      • Wait for this thread to die

    • void join(long milli)

    • void run()

    • void start()

  • Static methods

    • int activeCount()

      • Returns an estimate of the number of active threads in the current thread's ThreadGroup and its subgroups

    • Thread currentThread()

      • Returns a reference to the currently executing thread object.

    • void sleep(long milli)

      • Causes the currently executing thread to sleep

    • void yield()

      • A hint to the scheduler that the current thread is willing to yield its current use of a processor

    • void dumpStack()

      • Prints a stack trace of the current thread to the standard error stream

Synchronisation

  • Shared resources
  • Critical section
  • Mutual exclusion
  • Locking / mutex
  • Semaphore
  • Monitor
  • Race condition
  • Inter-thread communication
  • How Java achieve synchronisation
    • Object monitor
    • sychronized
      • Guard the critical section
    • Synchronised method
    • Synchronised block
  • How Java achieve ITC
    • wait(), notify(), notifyAll()