Threads in Java

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Threads in Java
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Java Threads

• A thread is a single sequential flow of control
  within a program.
• Some texts call a thread a lightweight process
• A process carries a lot of baggage a thread is
  finer grained

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Java Threads

• Useful for user interfaces that must remain
  responsive
• for servers with more than one simultaneous
  client
• for polling loops much more efficient!
• for increased parallel-processing performance
• when modeling a naturally concurrent, parallel,
  or asynchronous situation.

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Simple Thread Example

• Simplest way to use threads is to have a class
  which extends Thread
• And have a method called run()
• Create an instance of this class and call start()

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The Synchronized Keyword

• public synchronized void foo()
• bar()
• Is equivalent to
• public void foo()
• synchronized( this ) // this is the monitor
  object
• bar()

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Thread methods

• Java provides various mechanisms for concurrent
  Threads to coordinate their efforts
• sleep( long ms ) throws InterruptedException
• public static void yield()
• public synchronized void start()
• public final boolean isAlive()
• public final void join() throws
  InterruptedException
• public final void suspend() // deprecated.
• public final void resume() // deprecated.
• wait(lock), notify() and notifyAll()

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Java Thread Life Cycle
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Deadly Embrace

• A is waiting for B
• B is waiting for C
• C is waiting for A
• Everything stops! The curse of concurrent
  programming.