ReentrancyGuard.sol

/*
 * SPDX-License-Identitifer:    MIT
 */

pragma solidity ^0.4.24;

import "../common/UnstructuredStorage.sol";


contract ReentrancyGuard {
    using UnstructuredStorage for bytes32;

    /* Hardcoded constants to save gas
    bytes32 internal constant REENTRANCY_MUTEX_POSITION = keccak256("aragonOS.reentrancyGuard.mutex");
    */
    bytes32 private constant REENTRANCY_MUTEX_POSITION = 0xe855346402235fdd185c890e68d2c4ecad599b88587635ee285bce2fda58dacb;

    string private constant ERROR_REENTRANT = "REENTRANCY_REENTRANT_CALL";

    modifier nonReentrant() {
        // Ensure mutex is unlocked
        require(!REENTRANCY_MUTEX_POSITION.getStorageBool(), ERROR_REENTRANT);

        // Lock mutex before function call
        REENTRANCY_MUTEX_POSITION.setStorageBool(true);

        // Perform function call
        _;

        // Unlock mutex after function call
        REENTRANCY_MUTEX_POSITION.setStorageBool(false);
    }
}