Provide get_started statistic

bb8/src/api.rs

@@ -101,11 +101,17 @@ pub struct State {
 #[derive(Debug, Default)]
 #[non_exhaustive]
 pub struct Statistics {
-    /// Total gets performed that did not have to wait for a connection.
+    /// Total gets started.
+    ///
+    /// This counter is incremented before the `get` operation starts waiting,
+    /// so that it's possible to monitor the size of the queue by computing the
+    /// difference with the other `get_*` statistics.
+    pub get_started: u64,
+    /// Total gets completed that did not have to wait for a connection.
     pub get_direct: u64,
-    /// Total gets performed that had to wait for a connection available.
+    /// Total gets completed that had to wait for a connection available.
     pub get_waited: u64,
-    /// Total gets performed that timed out while waiting for a connection.
+    /// Total gets completed that timed out while waiting for a connection.
     pub get_timed_out: u64,
     /// Total time accumulated waiting for a connection.
     pub get_wait_time: Duration,
@@ -123,6 +129,18 @@ pub struct Statistics {
     pub connections_closed_idle_timeout: u64,
 }
 
+impl Statistics {
+    /// Total pending gets waiting for a connection.
+    pub fn pending_gets(&self) -> u64 {
+        self.get_started - self.completed_gets()
+    }
+
+    /// Total gets completed.
+    pub fn completed_gets(&self) -> u64 {
+        self.get_direct + self.get_waited + self.get_timed_out
+    }
+}
+
 /// A builder for a connection pool.
 #[derive(Debug)]
 pub struct Builder<M: ManageConnection> {

bb8/src/inner.rs

@@ -125,6 +125,8 @@ where
             }
         };
 
+        self.inner.statistics.record_get_started();
+
         let result = match timeout(self.inner.statics.connection_timeout, future).await {
             Ok(result) => result,
             _ => {

bb8/src/internals.rs

@@ -320,6 +320,7 @@ impl<C: Send> From<Conn<C>> for IdleConn<C> {
 
 #[derive(Default)]
 pub(crate) struct AtomicStatistics {
+    pub(crate) get_started: AtomicU64,
     pub(crate) get_direct: AtomicU64,
     pub(crate) get_waited: AtomicU64,
     pub(crate) get_timed_out: AtomicU64,
@@ -332,6 +333,10 @@ pub(crate) struct AtomicStatistics {
 }
 
 impl AtomicStatistics {
+    pub(crate) fn record_get_started(&self) {
+        self.get_started.fetch_add(1, Ordering::Relaxed);
+    }
+
     pub(crate) fn record_get(&self, kind: StatsGetKind, wait_time_start: Option<Instant>) {
         match kind {
             StatsGetKind::Direct => self.get_direct.fetch_add(1, Ordering::Relaxed),
@@ -370,6 +375,7 @@ impl AtomicStatistics {
 impl From<&AtomicStatistics> for Statistics {
     fn from(item: &AtomicStatistics) -> Self {
         Self {
+            get_started: item.get_started.load(Ordering::Relaxed),
             get_direct: item.get_direct.load(Ordering::Relaxed),
             get_waited: item.get_waited.load(Ordering::Relaxed),
             get_timed_out: item.get_timed_out.load(Ordering::Relaxed),