java threads for easy learn and develop

learning java easy

1. Today’s Agenda
Quick Review
Finish Java Threads
The CS Problem
Advanced Topics in Software Engineering 1

2. Quick Review
What are the two approaches to creating Java
threads?
Advanced Topics in Software Engineering 2

3. Advanced Topics in Software Engineering 3
Java Threads
 Thread Creation
 Thread Synchronization
 Thread States And Scheduling
 Short Demo

4. Advanced Topics in Software Engineering 4
Thread Creation
There are two ways to create a thread in Java:
 Extend the Thread class
 Implement the Runnable interface

5. Advanced Topics in Software Engineering 5
The Thread class
class A extends Thread {
public A (String name) { super (name); }
public void run () {
System.out.println(“My name is ” + getName());
}
}
class B {
public static void main (String [] args) {
A a = new A (“mud”);
a.start ();
}
}

6. Advanced Topics in Software Engineering 6
The Runnable interface
class A extends ... implements Runnable {
public void run () {
System.out.println(“My name is ” + getName () );
}
}
class B {
public static void main (String [] args) {
A a = new A ();
Thread t = new Thread (a, “mud, too”);
t.start ();
}
}

7. Advanced Topics in Software Engineering 7
Java Threads
 Thread Creation
 Thread Synchronization
 Thread States And Scheduling
 Short Demo

8. Advanced Topics in Software Engineering 8
Lock
Each Java object is implicitly associated with a lock.
To invoke a synchronized method of an object, a
thread must obtain the lock associated with this
object.
The lock is not released until the execution of the
method completes.
The locking mechanism ensures that at any given
time, at most one thread can execute any
synchronized method of an object.
Important: Lock is per object (NOT per method)!

9. Advanced Topics in Software Engineering 9
wait, notify and notifyAll
The execution of wait on an object causes the
current thread to wait until some other thread to
call notify or notifyAll.
A thread must own the object lock before it invokes
wait on an object. The execution of wait will also
release the lock.
When a waiting thread is notified, it has to compete
and reacquire the object lock before it continues
execution.
What’s the difference between notify and notifyAll?

10. Advanced Topics in Software Engineering 10
join
A thread t1 can wait until another thread t2 to
terminate.
t1 t2
t2.join ()
end

11. Advanced Topics in Software Engineering 11
interrupt
interrupt allows one thread to send a signal to
another thread.
It will set the thread’s interrupt status flag, and will
throw a ThreadInterrupted exception if necessary .
The receiver thread can check the status flag or
catch the exception, and then take appropriate
actions.

12. Advanced Topics in Software Engineering 12
Other Thread methods
Method sleep puts the running thread into sleep,
releasing the CPU.
Method suspend suspends the execution of a thread,
which can be resumed later by another thread using
method resume.
Method stop ends the execution of a thread.
Note that suspend, resume, and stop has been
deprecated in Java 2. (For more info, refer to
http://java.sun.com/j2se/1.4.1/docs/guide/misc/threadPrimitiveDeprecation.html.)

13. Advanced Topics in Software Engineering 13
Daemon Thread
A daemon thread is used to perform some services
(e.g. cleanup) for other threads.
Any thread can be marked as a daemon thread using
setDaemon (true).
A program terminates when all its non-daemon
threads terminate, meaning that daemon threads die
when all non-daemon threads die.

14. Advanced Topics in Software Engineering 14
Java Threads
 Thread Creation
 Thread Synchronization
 Thread States And Scheduling
 Short Demo

15. Advanced Topics in Software Engineering 15
State Transition Diagram
suspend
blocked
new runnable running
suspended blocked
dead
start scheduled
CS, yield
IO, sleep
wait, join
s
t
o
p
suspend
stop, run ends
s
u
s
p
e
n
d
r
e
s
u
m
e
stop
IO completes,
sleep expires,
notify, notifyAll,
join completes
I
O

c
o
m
p
l
e
t
e
s
stop
s
u
s
p
e
n
d
stop
resum
e

16. Advanced Topics in Software Engineering 16
Scheduling
In general, there are two types of scheduling: non-
preemptive scheduling, and preemptive scheduling.
In non-preemptive scheduling, a thread runs until it
terminates, stops, blocks, suspends, or yields.
In preemptive scheduling, even if the current thread
is still running, a context switch will occur when its
time slice is used up.

17. Advanced Topics in Software Engineering 17
Priorities
Each thread has a priority that also affects their
scheduling to run.
If a thread of a higher priority enters the runnable
set, the currently running thread will be preempted
by the new thread.

18. Advanced Topics in Software Engineering 18
Java Threads
 Thread Creation
 Thread Synchronization
 Thread States And Scheduling
 Short Demo