Fixes the concurrency issue of calling the Next() proxy target on RRB
#2409
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…ound robin balancer
Codecov ReportBase: 92.84% // Head: 92.87% // Increases project coverage by
Additional details and impacted files@@ Coverage Diff @@
## master #2409 +/- ##
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+ Coverage 92.84% 92.87% +0.02%
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Files 39 39
Lines 4503 4519 +16
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+ Hits 4181 4197 +16
Misses 234 234
Partials 88 88
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@bbasic thanks. would it be too much to ask to tweak some other things there also?
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- fixed concurrency issue in `AddTarget()` - moved `rand.New()` to the random balancer initializer func. - internal code reorganized eliminating unnecessary pointer redirection - employing `sync.Mutex` instead of `RWMutex` which brings additional overhead of tracking readers and writers. No need for that since the guarded code has no long-running operations, hence no realistic congestion. - added additional guards without which the code would otherwise panic (e.g., the case where a random value is calculation when targets list is empty) - added descriptions for func return values, what to expect in which case.
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Hi @aldas |
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and thank you for doing the other parts too! |
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Round Robin Balancer (RRB)
Next()implementation did not properly use synchronization mechanisms to ensure right values are visible between concurrently executed code entering the same critical section.Previous use of an atomic add to update the index value without also using an atomic load to read it is incorrect use of atomic synchronization (stale values are read in go-routines).
The index value, obviously, depends on the size of the
targetsslice.If between index calculation and getting a value by index from the slice a target was removed and the index pointed to the last element then a panic due to out of bounds will be the result.
Hence, the logic must be guarded with the semaphore.