openzeppelin-contracts/contracts/ReentrancyGuard.sol

pragma solidity ^0.4.8;

/// @title Helps contracts guard agains rentrancy attacks.
/// @author Remco Bloemen <remco@2π.com>
/// @notice If you mark a function `nonReentrant`, you should also
/// mark it `external`.
contract ReentrancyGuard {

  /// @dev We use a single lock for the whole contract.
  bool private rentrancy_lock = false;

  /// Prevent contract from calling itself, directly or indirectly.
  /// @notice If you mark a function `nonReentrant`, you should also
  /// mark it `external`. Calling one nonReentrant function from
  /// another is not supported. Instead, you can implement a
  /// `private` function doing the actual work, and a `external`
  /// wrapper marked as `nonReentrant`.
  modifier nonReentrant() {
    if(rentrancy_lock == false) {
      rentrancy_lock = true;
      _;
      rentrancy_lock = false;
    } else {
      throw;
    }
  }

}