eth/downloader: dereference discarded statesync request #15545
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fjl
requested changes
Nov 27, 2017
| // Shift out the first request, but also set the emptied slot to nil for GC | ||
| copy(finished, finished[1:]) | ||
| finished[len(finished)-1] = nil | ||
| finished = finished[:len(finished)-1] |
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You can get the same effect using
finished = append(finished[:0:len(finished)-1], finished[1:]...)There was a problem hiding this comment.
Actually, this full format seems to reduce the capacity too, meaning it would be a reallocation of the underlying buffer. Am I missing something?
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I suggested this because I thought you want to avoid growing the slice indefinitely. The threeway slice expression does this.
If all you want is setting the unused element to nil, your solution is OK.
It's hard to decide, I want to keep the code compact. This operation isn't worth three lines + comment.
fjl
approved these changes
Jan 2, 2018
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In the state synchronization structure of the downloader we are maintaining a
finishedslice containing all the currently pending responses (or timeouts) to state requests. Whenever the state processor accepts a pending item, we shift the entire slice to the left.However, since
finishedis backed by a single array internally, reducing the length by one will still keep the last item in a live (alas currently unreachable) array, and as such will keep a live memory reference to it. This in theory shouldn't matter much as it will soon enough be overwritten, but given our memory problems during sync, I'd rather avoid any such dangling GC references.