Semaphores and store-room problem.

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ppp - 15 Jan 2007 21:17 GMT

Hi, I think about solution of my exercise. Here it is:

There is product which contains three components: a, b and c. There are
3 processes (A, B and C) - each of them product one part (e.g. A create
one part a) and put it into store-room. There is also process M, which
takes one of each components and create product.
I have to do this using semaphores, but i wish to use least of them.
Maybe some of you have solution of this? I will be thankfull for any
help.

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Knute Johnson - 16 Jan 2007 01:27 GMT

> Hi, I think about solution of my exercise. Here it is:
>
[quoted text clipped - 5 lines]
> Maybe some of you have solution of this? I will be thankfull for any
> help.

I assume that you want to wait until you have (a,b,c) finishe before you
call M?

In that case the three parts (a,b,c) should each have a semaphore with
one permit that the part holds until it is complete. When it is
complete then it releases the semaphore and M can acquire all three
before making the product.

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Knute Johnson
email s/nospam/knute/

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ppp - 16 Jan 2007 10:02 GMT

Knute Johnson napisal(a):

> > Hi, I think about solution of my exercise. Here it is:
> >
[quoted text clipped - 18 lines]
> Knute Johnson
> email s/nospam/knute/

Yes, but buffer size is limited e.g. 10, and I don't know how to
prevent stack a b c (a must wait when a=8, b=1, and c=0)

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Knute Johnson - 16 Jan 2007 17:35 GMT

> Knute Johnson napisal(a):
>>> Hi, I think about solution of my exercise. Here it is:
[quoted text clipped - 22 lines]
> Yes, but buffer size is limited e.g. 10, and I don't know how to
> prevent stack a b c (a must wait when a=8, b=1, and c=0)

You need to look at Semaphore in the documentation, that's the first
thing. I don't really know how your program is going to work because
you haven't told us. From what little I know about what you want to do,
I would use a different Semaphore for each type of part. If the whole
takes 8 a parts then you will need 8 permits in the Semaphore.

Logic flow:

A acquires permits, starts building a parts, when each part is complete
it releases a permit.

B does same

C does same

M waits until it can acquire all 3 semaphores then makes product and
when it is done it releases all semaphores

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Knute Johnson
email s/nospam/knute/

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Semaphores and store-room problem.

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