refactor(npm): improve locking around updating npm resolution (#24104)

Introduces a `SyncReadAsyncWriteLock` to make it harder to write to the
npm resolution without first waiting async in a queue. For the npm
resolution, reading synchronously is fine, but when updating, someone
should wait async, clone the data, then write the data at the end back.

1 files changed, 35 insertions, 0 deletions

diff --git a/cli/util/sync/atomic_flag.rs b/cli/util/sync/atomic_flag.rs
new file mode 100644
index 000000000..75396dcf4
--- /dev/null
+++ b/cli/util/sync/atomic_flag.rs
@@ -0,0 +1,35 @@
+// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
+
+use std::sync::atomic::AtomicBool;
+use std::sync::atomic::Ordering;
+
+/// Simplifies the use of an atomic boolean as a flag.
+#[derive(Debug, Default)]
+pub struct AtomicFlag(AtomicBool);
+
+impl AtomicFlag {
+  /// Raises the flag returning if the raise was successful.
+  pub fn raise(&self) -> bool {
+    !self.0.swap(true, Ordering::SeqCst)
+  }
+
+  /// Gets if the flag is raised.
+  pub fn is_raised(&self) -> bool {
+    self.0.load(Ordering::SeqCst)
+  }
+}
+
+#[cfg(test)]
+mod test {
+  use super::*;
+
+  #[test]
+  fn atomic_flag_raises() {
+    let flag = AtomicFlag::default();
+    assert!(!flag.is_raised()); // false by default
+    assert!(flag.raise());
+    assert!(flag.is_raised());
+    assert!(!flag.raise());
+    assert!(flag.is_raised());
+  }
+}