openzeppelin-contracts/contracts/lifecycle/Pausable.sol

pragma solidity ^0.4.24;

import "../access/roles/PauserRole.sol";


/**
 * @title Pausable
 * @dev Base contract which allows children to implement an emergency stop mechanism.
 */
contract Pausable is PauserRole {
  event Paused();
  event Unpaused();

  bool private _paused = false;


  /**
   * @return true if the contract is paused, false otherwise.
   */
  function paused() public view returns(bool) {
    return _paused;
  }

  /**
   * @dev Modifier to make a function callable only when the contract is not paused.
   */
  modifier whenNotPaused() {
    require(!_paused);
    _;
  }

  /**
   * @dev Modifier to make a function callable only when the contract is paused.
   */
  modifier whenPaused() {
    require(_paused);
    _;
  }

  /**
   * @dev called by the owner to pause, triggers stopped state
   */
  function pause() public onlyPauser whenNotPaused {
    _paused = true;
    emit Paused();
  }

  /**
   * @dev called by the owner to unpause, returns to normal state
   */
  function unpause() public onlyPauser whenPaused {
    _paused = false;
    emit Unpaused();
  }
}