[erlang-questions] Semaphores

Danesh Daroui <>
Thu Mar 15 14:27:59 CET 2007


Christian S wrote:
>>
>> Well, it depends on. Sometimes semaphores can be a simple a good
>> solution if they are used with care. But of course message passing is
>> more advanced and general than semaphores.
>>
>
> I find message passing less advanced, I make fewer mistakes when using 
> it.
>
>>
>> Sorry, I explained bad in my previous email. Semaphores can be used
>> *not* only for sharing data but for other tasks, mainly synchronization.
>> In my sample file you can find a sample for barrier synchronization
>> using semaphores.
>>
>
> Do you have any examples of tasks that you solve using your semaphores?
>

Sure. Please take a look at my previous post. The semaphore source file 
is attached. There is also a file which is "semaphore_test.erl". In this 
file you can find an example about how to use this semaphore module. 
Also in that file "Barrier Synchronization" problem has been solved 
using semaphores. "Barrier Synchronization" is used to synchronize some 
processes where they do not have same speed to reach a point. So faster 
processes who reach a point (when they are done with a task) should wait 
for slower processes and when slowest process is done, all will begin 
from that point again. There are many classic examples like "Dining 
Philosophers", "Producers and Consumers" etc. which have been solved by 
semaphores. But, please pay attention that I don't want to defend 
semaphores against other modern techniques like message passing and so 
on. There is no doubt that modern techniques are more practical and 
efficient, but I thought that there might be programmers and tasks that 
could be done even partly using semaphores, thats all.



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