# Global variables

## Gas price and oracle

**Gas price** (given in Mwei per gas unit) is a key parameter of Mangrove that determines the bounty of takers for removing a failing offer from an offer list. In order to make sure takers are consistently over-compensated for the gas used, it should be kept well above average `tx.gasprice`.

**Gas price** can be read from an outside Monitor Contract. When the governance wishes to do so, it **must** enable this feature by letting the monitor (if any) act as a gas price oracle. This can be done using the governance restricted function `setUseOracle` of Mangrove.

If monitoring the gas price is not enabled, or if the value returned by the monitor is ill formed, Mangrove will use its global `gasprice` parameter as fallback.

```solidity
// Sets whether Mangrove uses the monitor as oracle for `gasprice` and `density` values.
function setUseOracle(bool useOracle) external;

// Sets the gasprice (in Mwei, 26 bits).
function setGasprice(uint gasprice) external;

// Sets the monitor/oracle. The `monitor/oracle` can provide real-time values for `gasprice` and `density` to Mangrove. It can also receive liquidity event notifications.
function setMonitor(address monitor) external;
```

```solidity
event SetGasprice(uint value);   // Emitted when gas price is updated.
event SetMonitor(address value); // Emitted when a new monitor is set.
event SetUseOracle(bool value);  // Logs `true` if Mangrove is set to use an external monitor to read gasprice. Logs `false` otherwise.
```

**Important point**

If allowing the monitor to act as a gas price Oracle, Governance **must** have previously deployed a Monitor Contract and set its address in Mangrove's configuration.

### Other governance controlled setters

```solidity
// Sets the gasmax for Mangrove, the maximum amount of gas an offer can require to execute.
function setGasmax(uint gasmax) external;

// Sets a new governance address.
function setGovernance(address governanceAddress) external;

// Sets whether Mangrove notifies the Monitor when and offer is taken.
function setNotify(bool notify) external;

// Sets the maximum number of times a market order can recursively execute offers. This is a protection against stack overflows.
function setMaxRecursionDepth(uint maxRecursionDepth) external;

// Sets the maximum cumulative `gasreq` for failing offers during a market order before doing a partial fill.
function setMaxGasreqForFailingOffers(uint maxGasreqForFailingOffers) external;

// Kills the Mangrove instance. A dead instance cannot have offers executed or funds received, but offers can be retracted and funds can be withdrawn.
function kill() external;
```


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