Add metric when acquiring permit to make outbound request

Signed-off-by: Ryan Levick <ryan.levick@fermyon.com>

Author: rylev

crates/factor-outbound-http/src/spin.rs

@@ -105,7 +105,28 @@ impl spin_http::Host for crate::InstanceState {
         // Note: since we don't have access to the underlying connection, we can only
         // limit the number of concurrent requests, not connections.
         let permit = match &self.concurrent_outbound_connections_semaphore {
-            Some(s) => s.acquire().await.ok(),
+            Some(s) => {
+                // Try to acquire a permit without waiting first
+                // Keep track of whether we had to wait for metrics purposes.
+                let mut waited = false;
+                let permit = match s.try_acquire() {
+                    Ok(p) => Ok(p),
+                    // No available permits right now; wait for one
+                    Err(tokio::sync::TryAcquireError::NoPermits) => {
+                        waited = true;
+                        s.acquire().await.map_err(|_| ())
+                    }
+                    Err(_) => Err(()),
+                };
+                if permit.is_ok() {
+                    spin_telemetry::monotonic_counter!(
+                        outbound_http.acquired_permits = 1,
+                        interface = "spin",
+                        waited = waited
+                    );
+                }
+                permit.ok()
+            }
             None => None,
         };
         let resp = client.execute(req).await.map_err(log_reqwest_error)?;

crates/factor-outbound-http/src/wasi.rs

@@ -591,7 +591,28 @@ impl ConnectOptions {
 
         // If we're limiting concurrent outbound requests, acquire a permit
         let permit = match &self.concurrent_outbound_connections_semaphore {
-            Some(s) => s.clone().acquire_owned().await.ok(),
+            Some(s) => {
+                // Try to acquire a permit without waiting first
+                // Keep track of whether we had to wait for metrics purposes.
+                let mut waited = false;
+                let permit = match s.clone().try_acquire_owned() {
+                    Ok(p) => Ok(p),
+                    // No available permits right now; wait for one
+                    Err(tokio::sync::TryAcquireError::NoPermits) => {
+                        waited = true;
+                        s.clone().acquire_owned().await.map_err(|_| ())
+                    }
+                    Err(_) => Err(()),
+                };
+                if permit.is_ok() {
+                    spin_telemetry::monotonic_counter!(
+                        outbound_http.acquired_permits = 1,
+                        interface = "wasi",
+                        waited = waited
+                    );
+                }
+                permit.ok()
+            }
             None => None,
         };