Thread Control methods

1
Thread Control methods

• The thread class contains the methods for
  controlling threads
• Thread() create default thread
• Thread(target runnable ) creates new thread to
  run the target object
• void run() invoked by JVM to execute the thread
• void start() starts the thread
• void interrupt() interrupts this thread
• boolean isAlive() tests whether the thread is
  currently running
• void setPriority(int p) sets priority p ranging
  from 1 to 10 ) for this thread

2
Thread control methods

• void join() wait for this thread to finish
• void yield() causes this thread to temporarily
  pause and allow other threads to execute
• boolean isInterrupted() tests if the current
  thread has been interrupted
• Thread currentThread() returns a reference to the
  currently executing thread object

3
Note

• The Thread class also contains the stop(),
  suspend() and resume() methods. As of Java 2,
  these methods are deprecated ( or outdated)
  because they are known to be inherently unsafe.
• Instead of using the stop() method, you should
  assign null to a Thread variable to indicate that
  it is stopped.

4
yield()

• You can use yield() method to temporarily release
  time for other threads.
• For example, in run method,
• public void run()
• for( int I 1 I lt lastNum I)
• System.out.print( I)
• Thread.yield()
• Every time a number is printed, the print100
  thread is yield. So each number is followed by
  some characters

5
Sleep()

• The sleep(long mills) method puts the thread to
  sleep for the specified time in milliseconds.
• Example, in run() method
• public void run()
• for( int I 1 I lt lastNum I)
• System.out.print( I)
• try
• if( Igt50) Thread.sleep(1)
• catch( InterruptedException ex)
• Every time a number (gt50) is printed, the
  print100 thread is put to sleep for 1 millisecond

6
join()

• Use join method to force one thread to wait for
  another thread to finish.
• For example, in run() method
• public void run()
• for( I 1 Ilt lastNum I)
• System.out.print( I)
• try
• if ( I 50 ) printA.join()
• catch (InterruptedException ex)
• The number from 50 to 100 are printed after
  thread printA is finished.
• Who force who? Who wait for who?
• Current thread wait for thread printA

7
Thread state

• Thread can be in one of five states
• New, Ready, Running, Blocked, finished
• New when a thread is created
• Ready after calling start(). A thread is
  runnable but may not be running. The OS had to
  allocate time
• Running A ready thread begins executing
• Blocked several reasons, it can be reactivated
• it may have invoked the join(), sleep()
• Other thread may have invoked these methods
• May be waiting for an I/O operation to finish
• Finished if it completes the execution of its
  run() method

8
Find out state

• isAlive() method is used to find out the state of
  a thread. It returns true if a thread is in the
  Ready, Blocked, or Running state it returns
  false if a thread is new and has not started or
  if it is finished
• Interrupt() method interrupts a thread in the
  following way
• If a thread is currently in the Ready or Running
  state, its interripted falg is set
• If a thread is currently blocked, it is awakened
  and enters the Ready state, and a
  java.lang.InterruptedException is thrown

9
Thread priorities

• Java assigns every thread a priority
• By default, a thread inherits the priority of the
  thread that spawned it
• Increase or decrease the priority of any thread
  by using setPriority(int) method
• Priorities are numbers 1 -10
• Thread class has int constants MIN_PRIORTY,
  NORM_PRIORITY and MAX_PRIORITY representing 1,5
  and 10.
• JVM picks highest priority
• Lower-priority thread can run only when no
  higher-priority threads are running

10
Thread group

• A thread group is a set of thread
• You can group them and perform operation on
  entire group
• Use the ThreadGroup constructor to construct a
  thread group
• ThreadGroup g new ThreadGroup(Thread
  Group)
• This create a group with name Thread Group
• Place a thread in the group
• Thread t new Thread(g, newThreadClass(),
  label for the thread)
• To find out how many threads in a group are
  currently running
• Ssytem.out.println(The number of thread
  in the group g.activeCount())
• Each thread belongs to a thread group. By
  default, a newly created thread becomes a member
  of the current thread group that spawned it. To
  find which group it belongs to, use the
  getThreadGroup() method