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Update ReentrancyGuard for Istanbul Hard Fork (#1992)

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* Update ReentrancyGuard for Istanbul Hard Fork

Changes:
Added L37, `_guardCounter = 1;`

Rationale:
The planned _Istanbul Hard Fork_ will implement [EIP 2200](e4d4ea348e/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.

* Update CHANGELOG.md

Added note for change to ReentrancyGuard.sol

* Update ReentrancyGuard.sol

* Update CHANGELOG.md
This commit is contained in:
ericDeCourcy
2019-11-13 10:54:15 -07:00
committed by Nicolás Venturo
parent f90700f3f1
commit 33047ffddc
2 changed files with 5 additions and 0 deletions
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4
contracts/utils/ReentrancyGuard.sol
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@ -11,6 +11,9 @@ pragma solidity ^0.5.0;
* `nonReentrant` may not call one another. This can be worked around by making
* those functions `private`, and then adding `external` `nonReentrant` entry
* points to them.
*
* _Since v2.5.0:_ this module is now much more gas efficient, given net gas
* metering changes introduced in the Istanbul hardfork.
*/
contract ReentrancyGuard {
// counter to allow mutex lock with only one SSTORE operation
@ -34,5 +37,6 @@ contract ReentrancyGuard {
uint256 localCounter = _guardCounter;
_;
require(localCounter == _guardCounter, "ReentrancyGuard: reentrant call");
_guardCounter = 1;
}
}