Thread

Multithreading

Chapter 23

2

Introduction

•
Consider ability of human body to ___________

–
Breathing, heartbeat, chew gum, walk …

•
In many situations we need a computer to
multitask

•
Concurrency normally available in __________

•
Java provides built
-
in multithreading

–
Multithreading improves the ___________ of some
programs

3

Thread States: Life Cycle of a
Thread

•
__________________

state

–
New thread begins its life cycle in the new state

–
Remains in this state until program starts the
thread, placing it in the
runnable

state

•
runnable

state

–
A thread in this state is ___________ its task

•
waiting

state

–
A thread ___________ to this state to wait for
another thread to perform a task

4

Thread States: Life Cycle of a
Thread

•
__________________

state

–
A thread enters this state to wait for another
thread or for an amount of time to elapse

–
A thread in this state returns to the
___________

state when it is signaled by another thread or
when the timed interval expires

•
terminated

state

–
A
runnable

thread enters this state when it
_____________ its task


5

Operating System View Of
runnable

State

•
ready

state

–
____________ waiting for another thread

–
Waiting for the ______________ to assign the
thread a processor

6

Operating System View Of
runnable

State

•
running

state

–
Currently has a _________________ and is
executing

–
Often executes for a small amount of processor
time called a _______________________ before
transitioning back to the
ready

state

7

Thread Priorities and Thread
Scheduling

•
Java thread priority

–
Priority in range ______________

•
Timeslicing

–
Each thread assigned time on the processor (called
a
quantum
)

–
Keeps ______________ threads running


8

Priorities
and
Scheduling

Thread.MAX_PRIORITY

9

Creating and Executing Threads

•
Runnable

interface

–
Preferred means of creating a multithreaded
application

–
Declares method
_______________

–
Executed by an object that implements the
Executor

interface

•
Executor

interface

–
Declares method
___________________

–
Creates and manages a group of threads called
a thread pool

10

Creating and Executing Threads

•
ExecutorService

interface

–
______________________ of
Executor

that
declares other methods for managing the life cycle
of an
Executor

–
Can be created using
_______________

methods
of class
Executors

–
Method
shutdown

_______________ when tasks
are completed

11

Creating and Executing Threads

•
Executors

class

–
Method
newFixedThreadPool

creates a pool
consisting of a __________________________ of
threads

–
Method
newCachedThreadPool

creates a pool
that creates new threads
_____________________________

12

Creating and Executing Threads

•
PrintTask class
Figure 23.4

•
RunnableTester,
Figure 23.5

•
Demonstrates

–
____________
Thread
objects

–
Using
Thread

methods
___________
and
sleep

–
Creates 3 equal priority threads

–
Each is put to sleep for random number of
milliseconds

–
When awakened, it displays name, etc.

13

Producers and Consumers

•
Producer

–
Generating

_______________



•
Consumer

–
Receives and

_________________

the output

14

Synchronization

•
Problem

–
Sometimes the producer gets too far
____________ of the consumer

•
The objects produced fill up the holding area
(_____________)

•
The producer must wait for space to place objects

–
Sometimes the ______________ gets ahead of the
producer

•
There are no objects to be processed (_____________
buffer)

•
The consumer must wait for the producer

15

Thread Synchronization

•
Thread synchronization

–
Provided to the programmer with
_____________________

•
Exclusive access to a shared object

–
Implemented in Java using _____________

•
Lock

interface

–
lock

method obtains the lock, enforcing mutual
exclusion

–
unlock

method ________________ the lock

–
Class
ReentrantLock

implements the
Lock

interface


16

Thread Synchronization

•
Condition variables

–
If a thread holding the lock cannot continue with its
task until a condition is satisfied, the thread can wait
on a ____________________

–
Create by calling
Lock

method
newCondition

–
Represented by an object that implements the
___________________

interface

17

Thread Synchronization


•
Condition interface

–
Declares methods
await
, to make a thread wait,

–
____________________
, to wake up a waiting
thread, and

–
signalAll
, to wake up all waiting threads

18

Producer/Consumer Relationship
without Synchronization

•
Buffer

–
____________________ memory region

•
Producer thread

–
Generates _____________ to add to buffer

–
Calls
wait
if consumer has not read previous message in
buffer

–
Writes to empty buffer and calls
____________
for
consumer

•
Consumer thread

–
Reads data from buffer

–
Calls
wait
if buffer ________________

•
Synchronize threads to avoid corrupted data

19

Producer/Consumer Relationship without
Synchronization

•
View source code which establishes

–
Buffer,
Figure 23.6

•
An interface which specifies
get
and
set
methods

–
Producer,
Figure 23.7

•
___________________ of
Thread

•
Uses a shared
Buffer

object

•
Method
run

is _________________ from
Thread

class

•
Uses
Buffer.set()

method

–
Consumer,
Figure 23.8

•
Also a subclass of
Thread
, also uses shared
Buffer

•
Uses the
Buffer.get()

method

20

Producer/Consumer Relationship without
Synchronization

•
View
Figure 23.9

which
implements
the
Buffer
interface

–
Implements the
_________________
methods

•
This
UnsynchronizedBuffer

object is used
in
Figure 23.10

program

–
Buffer

object declared, instantiated

–
Also
Producer

and
Consumer

objects

–
Both threads call method
start()


21

Producer/Consumer Relationship without
Synchronization

•
Example randomly called producer and
consumer

•
You should note that in some cases the data
was _________________

–
Consumer reads values _________ producer
generates

–
Consumer _______________ a value

–
Consumer reads same value multiple times

•
We need to deal with problem so data is not
corrupted

22

Producer/Consumer Relationship
with

Synchronization

•
Solution is to _________________ the
producer and consumer objects

•
Figure 23.11

implements a buffer and
synchronizes

–
Consumer consumes only ______ produces a
value

–
Producer produces a value only after consumer
consumes ____________ value produced

–
Condition variable
occupiedBufferCount

determines whose turn it is

•
Program which uses this,
Figure 23.12

23

Using Thread Methods

•
Create
Wait

class

•
Has
_______________

methods

•
Provide capability to have another application
______________ for a certain amount of time

•
Note
Example
to act as a simple timer.

24

Circular Buffer

•
Features

–
Multiple memory cells

–
Produce item if one or more empty cells

–
Consume item if one or more filled cells

•
Caveats

–
Producer and consumers must be relatively
______________ speed

•
Otherwise buffer fills up or stays empty

–
Synchronization still necessary

–
Seek to optimize buffer size

•
______________________ thread
-
wait time

25

Circular Buffer

•
Circular Buffer class
Figure 23.13

–
______________ for mutual exclusion

–
Condition variables to control writing and reading

–
Circular buffer; provides three spaces for data

–
Obtain the lock ____________ writing data to the
circular buffer

–
Wait until a buffer space is ___________

–
Impose circularity of the buffer

–
___________ waiting thread when to read data
from buffer

–
Release lock

26

Circular Buffer

•
Circular Buffer test,
Figure 23.14

–
Create instance of circular buffer

–
Execute producer, consumer in separate threads

27

Daemon Threads

•
Run for benefit of _____________________

–
Do not prevent program from terminating

–
__________________ is a daemon thread

•
Set daemon thread with method
setDaemon

–
Must be done at __________________ time

•
Do not assign _____________ tasks to daemon
thread

–
Will be terminated without warning

–
May prevent those tasks from completing properly

28

Runnable

Interface

•
May be necessary to __________ a class that
already extends a class other than
Thread

•
Java does not allow a class to extend more
than one class at a time

–
Implement
Runnable
for ____________ support

•
Program that uses a
Runnable
object to
control a thread

–
Creates a
Thread

object

–
Associates the
Runnable

object with that
Thread

class

29

Runnable

Interface

•
Illustration of using a
Runnable
interface

–
Figure 23.18

•
Note methods
start
,
stop
,
run