Clear DefinitionsEmergency Stop Pattern
1 min read
Pronunciation
[ih-MUR-juhn-see stop pat-ern]
Analogy
Think of an emergency stop like a train’s dead man’s switch—it immediately stops all operations when triggered to prevent accidents.
Definition
A smart contract design that allows authorized parties to halt contract operations in case of detected vulnerabilities or anomalous behavior.
Key Points Intro
The Emergency Stop Pattern enables rapid response through:
Key Points
Circuit breaker variable: A boolean flag (e.g., `stopped`) controlling function execution.
Modifier integration: Functions check `require(!stopped)` before critical logic.
Authorized control: Only designated roles (owner, guardian) can toggle the flag.
Fail-safe mode: Halts state‑changing operations while allowing withdrawals or refunds.
Example
```
modifier whenRunning { require(!stopped, "Paused"); _; }
function transfer(...) external whenRunning { ... }
function toggleEmergency() external onlyOwner { stopped = !stopped; }
```
Technical Deep Dive
Implement a `stopped` state variable and a `whenRunning` modifier. Wrap all mutative functions with the modifier. Provide `toggleEmergency()` guarded by an `onlyOwner` or multisig role. Ensure withdrawal or refund functions use a separate `whenStopped` modifier if users must recover funds while paused.
Security Warning
If the owner key is compromised, an attacker can freeze the contract indefinitely; use multisig or time‑lock on toggles.
Caveat
Pausing too broadly can lock out legitimate use; carefully choose which functions respect the stop flag.
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