[R4R]: Redesign triePrefetcher to make it thread safe #972
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too many channels and messages communication, actually only |
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There are 2 types of triePrefetcher instances: 1.New created triePrefetcher: it is key to do trie prefetch to speed up validation phase. 2.Copied triePrefetcher: it only copy the prefetched trie information, actually it won't do prefetch at all, the copied tries are all kept in p.fetches. Here we try to improve the new created one, to make it concurrent safe, while the copied one's behavior stay unchanged(its logic is very simple). As commented in triePrefetcher struct, its APIs are not thread safe. So callers should make sure the created triePrefetcher should be used within a single routine. As we are trying to improve triePrefetcher, we would use it concurrently, so it is necessary to redesign it for concurrent access. The design is simple: ** start a mainLoop to do all the work, APIs just send channel message. Others: ** remove the metrics copy, since it is useless for copied triePrefetcher ** for trie(), only get subfetcher through channel to reduce the workload of mainloop
** make close concurrent safe ** fix potential deadlock
For APIs like: trie(), copy(), used(), it is simpler and more efficient to use a RWMutex instead of channel communicaton. Since the mainLoop would be busy handling trie request, while these trie request can be processed in parallism. We would only keep prefetch and close within the mainLoop, since they could update the fetchers
trie prefetcher’s behavior has changed, prefetch() won't create subfetcher immediately. it is reasonable, but break the UT, to fix the failed UT
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This was referenced Jul 28, 2022
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Description
There are 2 types of triePrefetcher instances.
1.New created
triePrefetcher: it is the one to do trie prefetch to speed up validation phase.2.Copied
triePrefetcher: it just do a copy of the prefetched trie, it won't do prefetch at all. The copied tries are all kept in p.fetches.In thie PR, we try to improve the new created one, to make it concurrent safe, while the copied one's behavior stay unchanged(its logic is very simple).
Rationale
As commented in
triePrefetcherstruct, its APIs are not thread safe. So callers should make sure the created triePrefetcher should be used within a single routine. As we are trying to improve triePrefetcher, we would use it concurrently, so it is necessary to redesign it for concurrent access.The redesigned workflow:
1.start a mainLoop to do the real trie prefetch work, caller could schedule prefetch request through channel message.
2.as the trie prefetch close operation is only allowed to do once and will be processed in the mainLoop too, since it will update the fetchers informantion.
3.The other operations will be done outside of the mainLoop for performance concern, since mainLoop could be too busy if all the works are done within the mainLoop. The action lists are: trie(),used(), copy(), these actions can be done in parallel with a simple read lock.
There is no obvious performance impact.
Changes
No impact to users.