mut-global utility

Author: devrandom

lightning/Cargo.toml

@@ -50,6 +50,7 @@ backtrace = { version = "0.3", optional = true }
 
 core2 = { version = "0.3.0", optional = true, default-features = false }
 libm = { version = "0.2", optional = true, default-features = false }
+delegate = "0.12.0"
 
 [dev-dependencies]
 regex = "1.5.6"

lightning/src/util/mod.rs

@@ -15,6 +15,8 @@ pub(crate) mod fuzz_wrappers;
 #[macro_use]
 pub mod ser_macros;
 
+pub mod mut_global;
+
 pub mod errors;
 pub mod ser;
 pub mod message_signing;

lightning/src/util/mut_global.rs

@@ -0,0 +1,73 @@
+//! An unsafe global variable that can be set exactly once.
+//!
+//! Used for testing purposes only.
+
+use std::sync::Mutex;
+
+/// A global variable that can be set exactly once.
+pub struct MutGlobal<T> {
+	value: Mutex<Option<T>>,
+}
+
+impl<T: Clone> MutGlobal<T> {
+	/// Create a new `MutGlobal` with no value set.
+	pub const fn new() -> Self {
+		Self {
+			value: Mutex::new(None),
+		}
+	}
+
+	/// Set the value of the global variable.
+	///
+	/// Ignores any attempt to set the value more than once.
+	pub fn set(&self, value: T) {
+		let mut lock = self.value.lock().unwrap();
+		if lock.is_none() {
+			*lock = Some(value);
+		}
+	}
+
+	/// Get the value of the global variable.
+	///
+	/// # Panics
+	///
+	/// Panics if the value has not been set.
+	pub fn get(&self) -> T {
+		self.value
+			.lock()
+			.unwrap()
+			.clone()
+			.expect("not set")
+	}
+
+	/// Whether a value was set
+	pub fn is_set(&self) -> bool {
+		self.value.lock().unwrap().is_some()
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn test() {
+		let v = MutGlobal::<u8>::new();
+		assert!(!v.is_set());
+		v.set(42);
+		assert_eq!(v.get(), 42);
+		v.set(43);
+		assert_eq!(v.get(), 42);
+	}
+
+	static G: MutGlobal<u8> = MutGlobal::new();
+
+	#[test]
+	fn test_global() {
+		assert!(!G.is_set());
+		G.set(42);
+		assert_eq!(G.get(), 42);
+		G.set(43);
+		assert_eq!(G.get(), 42);
+	}
+}