On 2019-07-29, at 08:45:19, [email protected] wrote: > > I have a program which obtains a Memory Chunk, which is carved into a queue > of 256 > byte fixed length entries. I could have used a Data space. > . > In 31 Bit storage is the control information for the 64Bit Memory Chunk queue. > The 31 Bit storage control structure has the beginning address of the Memory > Chunk, the Ending Address Of the Memory Chunk, the number of fixed length > entries > an Ordinal Number (INDEX) and some state data. > . > The ordinal Number is used to index into the Memory Chunk of fixed length > entries > (queue) and is incremented using Compare and Swap (CS). > The program never searches the queue to find an available slot - it always > appends to the next entry by incrementing the ordinal number using compare > and swap.. > . > The memory chunk is used as a circular queue, meaning, when we reach the end > of > the queue (memory chunk), we resume by re-using the first entry at the top of > the queue > (wrap around). > We all-ways add new/next entries by incrementing the ordinal number and > indexing > into our Memory Chunk. > . > Here's My concern - > When we reach the end of the queue - the program needs to reset ther Ordinal > Index back to 0. > (so we can continue to add the next entry at the beginning of the queue).. > Is it better to test/reset this Index number before or after adding the last > entry in the queue ?Should there be a second Compare and Swap ? > I'll suggest that the reset to 0 should be done by the first and only CS. Otherwise the index might briefly contain an invalid value one unit beyond the end of the queue.
How do you deal with the possibility of queue overflow? -- gil
