Update ReentrancyGuard for Istanbul Hard Fork#1992
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nventuro merged 4 commits intoOpenZeppelin:masterfrom Nov 13, 2019
Merged
Update ReentrancyGuard for Istanbul Hard Fork#1992nventuro merged 4 commits intoOpenZeppelin:masterfrom
nventuro merged 4 commits intoOpenZeppelin:masterfrom
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Changes: Added L37, `_guardCounter = 1;` Rationale: The planned _Istanbul Hard Fork_ will implement [EIP 2200](https://github.com/ethereum/EIPs/blob/e4d4ea348e06c54d0075c400dc7b72430d427ff1/EIPS/eip-2200.md), which implements "net gas metering" for `sstore` operations. If the final value of `_guardCounter` is unchanged relative to the original value of it, a gas refund will be applied and charges for changing the value of `_guardCounter` will effectively not exist. This ends up being cheaper than the current implementation ONLY AFTER Istanbul. Before Istanbul, the added line actually ends up costing more gas. Note that if `_guardCounter` is `0` initially, the initial cost and subsequent refund will both be larger than if `_guardCounter` is `1` initially. Although in both cases, the net gas cost (`gasCost - gasRefund`) are equal, it's better in terms of cost to have both the gas cost and refund smaller, as there is some limit to the percentage of a gas refund that can actually be realized.
Contributor
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Thanks a lot @ericDeCourcy! Could you add an entry for this change on the changelog file? |
Added note for change to ReentrancyGuard.sol
Contributor
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Thanks! I took the liberty of changing it up a bit so that the improvements introduced by this PR are more evident by the reader, who may not be aware of the implications of the actual code change. I also added a note on the documentation for the module, to entice people to try out the new version. |
nventuro
approved these changes
Nov 13, 2019
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Changes:
Added L37,
_guardCounter = 1;Rationale:
The planned Istanbul Hard Fork will implement EIP 2200, which implements "net gas metering" for
sstoreoperations. If the final value of_guardCounteris unchanged relative to the original value of it, a gas refund will be applied and charges for changing the value of_guardCounterwill effectively not exist. This ends up being cheaper than the current implementation ONLY AFTER Istanbul. Before Istanbul, the added line actually ends up costing more gas.Note that if
_guardCounteris0initially, the initial cost and subsequent refund will both be larger than if_guardCounteris1initially. Although in both cases, the net gas cost (gasCost - gasRefund) are equal, it's better in terms of cost to have both the gas cost and refund smaller, as there is some limit to the percentage of a gas refund that can actually be realized.