java threads for easy learn and develop

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

Quick Review
 What are the two approaches to creating Java
threads?

Java Threads
 Thread Creation
 Thread Synchronization
 Thread States And Scheduling
 Short Demo

Thread Creation
There are two ways to create a thread in Java:
 Extend the Thread class
 Implement the Runnable interface

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 ();
}
}

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 ();
}
}

Java Threads
 Thread Creation
 Short Demo

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)!

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?

join
A thread t1 can wait until another thread t2 to
terminate.
t1 t2
t2.join ()
end

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.

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.)

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.

Java Threads
 Thread Creation
 Short Demo

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
IO
com
pletes
stop
s
u
s
p
e
n
d
stop
resume

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.

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.

Java Threads
 Thread Creation
 Short Demo

java threads for easy learn and develop

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