From: 7stud -- <bbxx789_05ss@...>
Date: 2007-10-14T00:11:14+09:00
Subject: Re: Is there a standard pattern for threaded access to a file?

Francis Cianfrocca wrote:
> On 10/12/07, Jon Handler <jhandler@shopping.com> wrote:
>> 1. Open the file
>> 2. Create 5 threads
>>
>> Each thread should read a line of the file and process it, but no 2
>> threads should get the same line.
> 
> 
> 
> Why are you doing this in the first place? Do you have a computer with 
> five
> processors and five memory buses?

According to pickaxe2, p. 135, your question is irrelevant:

"Finally, if your machine has more than one processor, Ruby threads 
won't take advantage of that fact--because they run in a single process, 
and in a single native thread, they are constrained to run on one 
processor at a time."

Perhaps a better question for the op is: does your processing result in 
any pauses in the code?  For instance, do you use the information in the 
log file to send requests to websites where you are waiting for a 
response?

Threads do not actually allow any code to run at the same time.  What 
really happens is that execution rapidly shifts from one thread to 
another, which gives the appearance that the threads are executing at 
the same time.

If you have five methods that each take 2 seconds to execute, and you 
run those five methods one after another, your program with take 10 
seconds to execute.  On the other hand, if you use five threads to 
execute those methods, your program will still take 10 seconds to 
execute.  For example, suppose each thread gets 1 second to execute 
before execution shifts to another thread, something like this will 
occur:

thread1: 1 sec
    |
    V
thread2: 1 sec
    |
    V
thread3: 1 sec
    |
    V
thread4: 1 sec
    |
    V
thread5: 1 sec
    |
    V
thread1: 1 sec
    |
    V
thread2: 1 sec
    |
    V
thread3: 1 sec
    |
    V
thread4: 1 sec
    |
    V
thread5: 1 sec


If you total up the time, it still takes 10 seconds for your program to 
execute when using five threads.  The only way threads help speed up 
execution is if there are pauses in your code where nothing is 
happening.  During those pauses, threads allow execution to shift to 
other code that is ready to execute.

-- 
Posted via http://www.ruby-forum.com/.