1. Multithreading Chapter 23

2. 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. 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. 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. 5 Operating System View Of runnable State ready state –____________ waiting for another thread –Waiting for the ______________ to assign the thread a processor

6. 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. 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. 8 Priorities and Scheduling Thread.MAX_PRIORITY

9. 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. 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. 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. 12 Creating and Executing Threads PrintTask class Figure 23.4Figure 23.4 RunnableTester, Figure 23.5Figure 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. 13 Producers and Consumers Producer –Generating _______________ Consumer –Receives and _________________ the output

14. 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. 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. 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. 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. 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. 19 Producer/Consumer Relationship without Synchronization View source code which establishes –Buffer, Figure 23.6Figure 23.6 An interface which specifies get and set methods –Producer, Figure 23.7Figure 23.7 ___________________ of Thread Uses a shared Buffer object Method run is _________________ from Thread class Uses Buffer.set() method –Consumer, Figure 23.8Figure 23.8 Also a subclass of Thread, also uses shared Buffer Uses the Buffer.get() method

20. 20 Producer/Consumer Relationship without Synchronization View Figure 23.9 which implements the Buffer interfaceFigure 23.9 –Implements the _________________ methods This UnsynchronizedBuffer object is used in Figure 23.10 programFigure 23.10 –Buffer object declared, instantiated –Also Producer and Consumer objects –Both threads call method start()

21. 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. 22 Producer/Consumer Relationship with Synchronization Solution is to _________________ the producer and consumer objects Figure 23.11 implements a buffer and synchronizesFigure 23.11 –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 23.12Figure 23.12

23. 23 Using Thread Methods Create Wait class Wait Has _______________ methods Provide capability to have another application ______________ for a certain amount of time Note Example to act as a simple timer.Example

24. 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. 25 Circular Buffer Circular Buffer class Figure 23.13Figure 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. 26 Circular Buffer Circular Buffer test, Figure 23.14Figure 23.14 –Create instance of circular buffer –Execute producer, consumer in separate threads

27. 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. 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. 29 Runnable Interface Illustration of using a Runnable interface –Figure 23.18Figure 23.18 Note methods start, stop, run