StackOverflow2013

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plurals

PO
primarykey
Id
19187035
data
AcceptedAnswerId
0
AnswerCount
0
ClosedDate
CommentCount
0
CommunityOwnedDate
CreationDate
2013-10-04T17:11:11.423
FavoriteCount
0
LastActivityDate
2013-10-04T19:21:30.043
LastEditDate
2013-10-04T19:21:30.043
LastEditorUserId
2847313
OwnerUserId
2847313
ParentId
19186670
PostTypeId
2
Score
2
ViewCount
0
LastEditorDisplayName
text
Body
It looks like a semaphore implemented using busy waiting. It works as follows: The producer and the consumer are working parallel to each other. The mutex is for mutual exclusion. That means, that only one of them is accessing the incommon datastructure at the same time. down() is checking if the mutex is free (== 1 in this case). It is checking this in a while loop like: <code>while (mutex < 1);</code>. If the mutex is finally free, it decreases its value (called "taking the mutex"). The other two semaphores are for making sure two things: <ol> <li>a consumer can only consume, if the datastructure is not empty</li> <li>a producer can only produce, if the datastructure is not full</li> </ol> This is necessary because one of both can be faster than the other one. With <code>down(&empty);</code> the producer checks if there are empty slots in the datastructure. If this is not the case he is not allowed to produce yet (busy waiting until a slot is free, meaning empty > 0). Otherwise he decreases empty and continues. When he added his produced item in the datastructure he incereases the value of full slots with <code>up(&full);</code>. With <code>down(&full);</code> the consumer checks if there are full slots to read. If this is not the case he is not allowed to read yet (busy waiting until a slot is full, meaning full > 0). Otherwise he decreases full and continues. When he consumed his item from the datastructure he increases the value of empty slots. Changing the order of ups and downs could cause a deadlock, because they could be waiting for each other infinitely long.
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Title
singulars
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1. This table or related slice is empty.
PostParentId
1. POProducer-consumer and how it works
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 PTQuestion
PostTypePostTypeId
1. PTAnswer
UserLastEditorUserId
1. USAnon
UserOwnerUserId
1. USAnon
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PostsAcceptedAnswerId
1. POProducer-consumer and how it works
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VotesPostIdCreationDate
1. VO
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1. This table or related slice is empty.

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