Expose client capacity; expand docs

Author: nickray

src/lib.rs

@@ -152,14 +152,23 @@ impl From<u8> for State {
 
 
 /// Do NOT implement this yourself! Use the macro `interchange!`.
+///
+/// At compile time, the client capacity is set by using the appropriate call
+/// to the `interchange!` macro. The application can then repeatedly call `claim`
+/// to obtain these clients.
 pub trait Interchange: Sized {
+    const CLIENT_CAPACITY: usize;
     type REQUEST: Clone;
     type RESPONSE: Clone;
     /// This is the constructor for a `(Requester, Responder)` pair.
     ///
     /// Returns singleton static instances until all that were allocated are
     /// used up, thereafter, `None` is returned.
     fn claim() -> Option<(Requester<Self>, Responder<Self>)>;
+
+    /// Method for debugging: how many allocated clients have not been claimed.
+    fn available_clients() -> usize;
+
     /// Method purely for testing - do not use in production
     ///
     /// Rationale: In production, interchanges are supposed to be set up

src/macros.rs

@@ -81,9 +81,12 @@ macro_rules! interchange {
                 static LAST_CLAIMED: AtomicUsize = AtomicUsize::new(0);
                 &LAST_CLAIMED
             }
+
         }
 
         impl $crate::Interchange for $Name {
+            const CLIENT_CAPACITY: usize = $N;
+
             type REQUEST = $REQUEST;
             type RESPONSE = $RESPONSE;
 
@@ -107,6 +110,10 @@ macro_rules! interchange {
                 }
             }
 
+            fn available_clients() -> usize {
+                Self::CLIENT_CAPACITY - Self::last_claimed().load(core::sync::atomic::Ordering::SeqCst)
+            }
+
             unsafe fn rq(self) -> Self::REQUEST {
                 match self {
                     Self::Request(request) => {