Fix connection count metrics

src/conn/pool/mod.rs

@@ -304,6 +304,10 @@ impl Pool {
             .metrics
             .create_failed
             .fetch_add(1, atomic::Ordering::Relaxed);
+        self.inner
+            .metrics
+            .connection_count
+            .store(exchange.exist, atomic::Ordering::Relaxed);
         // we just enabled the creation of a new connection!
         if let Some(w) = exchange.waiting.pop() {
             w.wake();
@@ -347,11 +351,6 @@ impl Pool {
 
         #[allow(unused_variables)] // `since` is only used when `hdrhistogram` is enabled
         while let Some(IdlingConn { mut conn, since }) = exchange.available.pop_back() {
-            self.inner
-                .metrics
-                .connections_in_pool
-                .fetch_sub(1, atomic::Ordering::Relaxed);
-
             if !conn.expired() {
                 #[cfg(feature = "hdrhistogram")]
                 self.inner
@@ -383,6 +382,11 @@ impl Pool {
             }
         }
 
+        self.inner
+            .metrics
+            .connections_in_pool
+            .store(exchange.available.len(), atomic::Ordering::Relaxed);
+
         // we didn't _immediately_ get one -- try to make one
         // we first try to just do a load so we don't do an unnecessary add then sub
         if exchange.exist < self.opts.pool_opts().constraints().max() {
@@ -392,7 +396,7 @@ impl Pool {
             self.inner
                 .metrics
                 .connection_count
-                .fetch_add(1, atomic::Ordering::Relaxed);
+                .store(exchange.exist, atomic::Ordering::Relaxed);
 
             let opts = self.opts.clone();
             #[cfg(feature = "hdrhistogram")]

src/conn/pool/recycler.rs

@@ -79,11 +79,6 @@ impl Future for Recycler {
                         .metrics
                         .connection_returned_to_pool
                         .fetch_add(1, Ordering::Relaxed);
-                    $self
-                        .inner
-                        .metrics
-                        .connections_in_pool
-                        .fetch_add(1, Ordering::Relaxed);
                     #[cfg(feature = "hdrhistogram")]
                     $self
                         .inner
@@ -93,6 +88,11 @@ impl Future for Recycler {
                         .unwrap()
                         .saturating_record($conn.inner.active_since.elapsed().as_micros() as u64);
                     exchange.available.push_back($conn.into());
+                    $self
+                        .inner
+                        .metrics
+                        .connections_in_pool
+                        .store(exchange.available.len(), Ordering::Relaxed);
                     if let Some(w) = exchange.waiting.pop() {
                         w.wake();
                     }
@@ -239,14 +239,13 @@ impl Future for Recycler {
         }
 
         if self.discarded != 0 {
-            self.inner
-                .metrics
-                .connection_count
-                .fetch_sub(self.discarded, Ordering::Relaxed);
-
             // we need to open up slots for new connctions to be established!
             let mut exchange = self.inner.exchange.lock().unwrap();
             exchange.exist -= self.discarded;
+            self.inner
+                .metrics
+                .connection_count
+                .store(exchange.exist, Ordering::Relaxed);
             for _ in 0..self.discarded {
                 if let Some(w) = exchange.waiting.pop() {
                     w.wake();

src/conn/pool/ttl_check_inerval.rs

@@ -70,6 +70,10 @@ impl TtlCheckInterval {
                 }
             }
             exchange.available = kept_available;
+            self.inner
+                .metrics
+                .connections_in_pool
+                .store(exchange.available.len(), Ordering::Relaxed);
             to_be_dropped
         };
 
@@ -79,6 +83,10 @@ impl TtlCheckInterval {
             tokio::spawn(idling_conn.conn.disconnect().then(move |_| {
                 let mut exchange = inner.exchange.lock().unwrap();
                 exchange.exist -= 1;
+                inner
+                    .metrics
+                    .connection_count
+                    .store(exchange.exist, Ordering::Relaxed);
                 ok::<_, ()>(())
             }));
         }