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Preparation -- Chapter 13 -- Concurrency

1. Study notes below and Chapter 13, but not section 8.
2. You can forget about MIMD/SIMD in this class.
3. Don't answer review questions on hardware. They are not on the Final.

Notes

Concurrency is often faked:

One single processor or computer can work as if it had many processors.

All modern operating systems use concurrency.

The introductory definitions and ideas in the book are important.

The various forms of hardware (MIMD and SIMD) and FORTRAN based concurrency can be ignored. Take our advanced architecture courses for this and/or talk to Dr. Gomez.

You need to understand


1. threads
2. semaphores,
3. monitors,
4. deadlocks
5. etc.

Because

1. They turn up all over the place: web sites, data bases, mail handlers, commercial transactions, system administration, etc..
2. They are used in interview questions.
3. They are a part of Java: [ Thread.html ]



Threads are easier than networks

[ 14723 ]

Ada

The ideas in Ada are simple to use
• rendezvous.
• Protected records
• The "message passing" model is simple, reliable, and flexible.



Some concurrency bugs are hard to find by testing.



1. Use simple and sure techniques: message passing and rendezvous.
2. Use logical model checking tools to look for the rare combinations of events that cause bugs.
3. Take CSci556: Formal Methods.



Small error in section 13.7.3 (page 587)

The book describes the syntax for synchronizing a statement from Java 1.0.

 		synchronized(expression)

 			statement

In later versions of Java a synchronized(...) clause can only be applied to a block.

 		synchronized(expression)

 		{

 			statements

 		}

The synchronized modifier can still be applied to classes and methods/functions.

Examples of Concurrency

Look in these directories: [ http://www.csci.csusb.edu/dick/cs320/sieve/ ] [ http://www.csci.csusb.edu/dick/cs320/crypto/ ]

Missing -- UNIX pipes



1. Simple to use message passing
2. Also in Java
3. Symbol |
4. Example

    			ls|grep 320



1. For A,B:commands, A|B::command=connects the output of A to the input of B and executes them in parallel.

   Examples

          ls|wc -l

   lists files and counts them. (ls =list, wc -l = count lines)

          ls|grep 320|wc -l

   list files, filters out those with '320' in the name and counts them.

          grep -l 320 *|wc -l

   counts the number of files with '320' inside them.

          ps -elf|grep $USER

   lists all processes and filters out those with your name in them... including the two processes 'ps -elf' and 'grep'.

. . . . . . . . . ( end of section Notes) <<Contents | End>>

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