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POCan only read one element at once of a circular buffer
 

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    <p>I have implemented the standard single consumer, single producer queue as a circular buffer in C consisting of an array and two indexes: one for read, one for write.</p> <p>My circular buffer is of the type that returns an error if you attempt to insert an item into a full queue and uses one empty slot to distinguish between an empty ring buffer and a full one.</p> <p>While debugging it I noticed it sometime slipped into a consistent state where you could only read a single item at a time before getting the return value that meant the buffer is full, even though there was an ongoing thread that does inserts all the time.</p> <p>I assumed I must have done something silly in implementation but could not find anything. I then decided to double check the logic and re-read the <a href="http://en.wikipedia.org/wiki/Circular_buffer#Always_Keep_One_Slot_Open" rel="nofollow noreferrer">Wikipedia value</a> that describes such queues.</p> <p>Much to my surprise, I noticed the following cryptic comment in the text:</p> <blockquote> <p>If you cannot read over the buffer border, you get a lot of situations where you can only read one element at once.</p> </blockquote> <p>So, if I understand the meaning correctly, this seems to indicate that this is some sort inherit problem with this way of implementing such a ring buffer.</p> <p>Alas, my feeble brain is at a lose to understand the root cause of this problem: why is this happening? what sequence of inserts and erases can get such a ring buffer into this state?</p> <p>You help is greatly appreciated.</p>
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