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openzeppelin-contracts/contracts/lifecycle/Pausable.sol

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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;
constructor() public {
_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();
}
}