full control of the microprocessor。 o To implement tasks that you want to run separately from the main program； you use threads。 o Each program that is started is a task and has a main thread from which you can start other threads。 o Threading is not difficult and easily implemented。 What is more difficult is synchroniza tion between the threads。 o Synchronization is not about the data； but about synchronizing access to code that modifies data that is shared。 If your data is not shared； you don’t need synchronization。 o In the context of a single application； you will use either the exclusive lock or the Monitor for synchronization。 o Locking code slows down the code。 You should keep the locks for the shortest time possible。 o To improve throughput； you can take a snapshot of the data。 o Higher…level synchronization abstractions are the reader/writer and producer/consumer architectures。 …………………………………………………………Page 391…………………………………………………………… C HA P TE R 1 3 ■ L E AR N IN G AB O U T M U L T IT HR E AD IN G 369 o Reader/writer locks are exclusive locks； but they separate code that reads from code that writes。 To improve code efficiency； reader/writer locks allow multiple readers； but only a single writer。 Reader/writer locks are effective only if； for the most part； you are reading data。 o Producer/consumer locks split the task of producing and consuming data into two sepa rate steps。 The API uses the producer/consumer concept extensively； examples are Windows。Forms and IAsyncResult。 o Deadlocks occur because timing changes cause your code to not be deterministic。 o Deadlocks can be partially avoided using Monitors； but the most effective way of avoiding deadlocks is to use the producer/consumer development technique。 This is because the producer/consumer architecture takes the approach of handing off data； rather than sharing data。 o Applications that multitask effectively are applications that have been designed using logic； rather than development techniques where you think up the code as you go along。 Some Things for You to Do The following is an exercise to help you apply what you learned in this chapter。 1。 Write a general architecture that generates a series using multiple threads。 For the first series； generate the square of all numbers between 1 and 100。 For the second series； generate the Fibonacci series。 That is； after two starting values； each number is the sum of the two preceding numbers。 The first Fibonacci numbers are 0； 1； 1； 2； 3； 5； 8； 13； 21； 34； 55； 89； 144； 233； 377； 610； 987； 1597； 2584； 4181； 6765； 10946； 17711； 28657； 46368； 75025； 121393； 196418； and 317811。 Outline the limits of multithreading when generating a series。 …………………………………………………………Page 392…………………………………………………………… …………………………………………………………Page 393…………………………………………………………… C H A P T E R 1 4 ■ ■ ■ Learning About Relational Database Data Literally hundreds of techniques； tips； tricks； and libraries are associated with relational data bases。 Covering relational databases would take an entire a book； and in fact； many books are devoted to that subject。 This chapter will cover the basics and give you enough knowledge to read and write to a database。 The focus of this chapter is to demonstrate accessing relational databases with ADO and the Visual Studio Dataset Designer。 Since we’ll need a database to work with； you’ll also learn how to create a database with Visual Basic Express。 A relational database stores data； such as the lottery numbers in Chapter 10’s example。 Building on that lottery…prediction example； in this chapter； you’ll see how to create a database application that reads and writes the lottery numbers； and associates winners with a particular lottery drawing。 Understanding Relational Databases As a beginner developer； one of your greatest challenges will be how to manage relational database data。 A relational database is an old piece of technology。 The relational model on which it is based was written in about 1969 （according to the relational model entry at http：//en。wikipedia。org/ wiki/Relational_model）。 A relational database is defined as follows （http：//en。wikipedia。org/ wiki/Relational_database）： Strictly； a relational database is merely a collection of relations （frequently called tables）。 Other items are frequently considered part of the database； as they help to organize and structure the data； in addition to forcing the database to conform to a set of requirements。 Relational Database Tables A relational database is a collection of tables。 When you were reading and writing a file in Chapter 10’s example； you were actually reading and writing a table of lottery numbers； which looked something like this： 371 …………………………………………………………Page 394…………………………………………………………… 372 CH AP T E R 1 4 ■ L E A R N I N G A B OU T R E L A TI O N AL DA TA B AS E D AT A 2000。05。31 5 6 13 23 25 37 43 2000。06。03 7 10 11 18 32 41 5 2000。06。07 15 23 24 28 38 39 45 2000。06。10 1 3 12 23 29 33 27 2000。06。14 2 4 13 19 39 45 26 2000。06。17 3 8 17 19 21 25 35