feat: implement Send for Scanner and some related types.

lib/src/scanner/mod.rs

@@ -162,6 +162,23 @@ pub struct Scanner<'r> {
     timeout: Option<Duration>,
 }
 
+/// `Scanner` implements [`Send`] but does not implement [`Sync`]. This means
+/// that transferring ownership of a `Scanner` between threads is safe, but
+/// accessing a `Scanner` from multiple threads concurrently is not.
+///
+/// Note that `&Scanner` (a shared reference) is not [`Send`] because allowing
+/// multiple threads to hold a reference to the same `Scanner` would be unsafe,
+/// as `Scanner` does not implement [`Sync`]. Without `Sync`, it is not
+/// guaranteed that shared access to the `Scanner` is thread-safe.
+///
+/// The reason `Scanner` does not automatically implement [`Send`] is due to the
+/// underlying [`ScanContext`] type, which contains some [`Rc`] instances. Since
+/// [`Rc`] is not thread-safe, `ScanContext` cannot be used safely by multiple
+/// threads. However, these non-thread-safe references are confined within the
+/// scanner and cannot be cloned or accessed from multiple threads at the same
+/// time.
+unsafe impl Send for Scanner<'_> {}
+
 impl<'r> Scanner<'r> {
     const DEFAULT_SCAN_TIMEOUT: u64 = 315_360_000;
 
@@ -867,6 +884,9 @@ pub struct ScanResults<'a, 'r> {
     data: ScannedData<'a>,
 }
 
+/// See the implementation of [`Send`] for [`Scanner`].
+unsafe impl Send for ScanResults<'_, '_> {}
+
 impl<'a, 'r> ScanResults<'a, 'r> {
     fn new(ctx: &'a ScanContext<'r>, data: ScannedData<'a>) -> Self {
         Self { ctx, data }
@@ -917,6 +937,9 @@ pub struct MatchingRules<'a, 'r> {
     iterator: Iter<'a, RuleId>,
 }
 
+/// See the implementation of [`Send`] for [`Scanner`].
+unsafe impl Send for MatchingRules<'_, '_> {}
+
 impl<'a, 'r> MatchingRules<'a, 'r> {
     fn new(ctx: &'a ScanContext<'r>, data: &'a ScannedData<'a>) -> Self {
         Self { ctx, data, iterator: ctx.non_private_matching_rules.iter() }
@@ -954,6 +977,9 @@ pub struct NonMatchingRules<'a, 'r> {
     len: usize,
 }
 
+/// See the implementation of [`Send`] for [`Scanner`].
+unsafe impl Send for NonMatchingRules<'_, '_> {}
+
 impl<'a, 'r> NonMatchingRules<'a, 'r> {
     fn new(ctx: &'a ScanContext<'r>, data: &'a ScannedData<'a>) -> Self {
         let num_rules = ctx.compiled_rules.num_rules();
@@ -1024,6 +1050,9 @@ pub struct ModuleOutputs<'a, 'r> {
     iterator: hash_map::Iter<'a, &'a str, Module>,
 }
 
+/// See the implementation of [`Send`] for [`Scanner`].
+unsafe impl Send for ModuleOutputs<'_, '_> {}
+
 impl<'a, 'r> ModuleOutputs<'a, 'r> {
     fn new(ctx: &'a ScanContext<'r>) -> Self {
         Self {