From 98b062e9b564f399fb06da935ea6d6e37fa1d3f5 Mon Sep 17 00:00:00 2001
From: Zain Kabani <zain.kabani@instacart.com>
Date: Wed, 24 May 2023 11:59:31 -0400
Subject: [PATCH 1/2] Add LIFO option for getting resources in the pool

---
 bb8/src/api.rs       | 20 ++++++++++++++++++++
 bb8/src/internals.rs | 14 +++++++++++---
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/bb8/src/api.rs b/bb8/src/api.rs
index f0d1b82..6dc8219 100644
--- a/bb8/src/api.rs
+++ b/bb8/src/api.rs
@@ -74,6 +74,14 @@ impl<M: ManageConnection> Pool<M> {
     }
 }
 
+#[derive(Debug)]
+pub enum QueueStrategy {
+    /// Last in first out
+    LIFO,
+    /// First in first out
+    FIFO,
+}
+
 /// A builder for a connection pool.
 #[derive(Debug)]
 pub struct Builder<M: ManageConnection> {
@@ -95,6 +103,8 @@ pub struct Builder<M: ManageConnection> {
     pub(crate) error_sink: Box<dyn ErrorSink<M::Error>>,
     /// The time interval used to wake up and reap connections.
     pub(crate) reaper_rate: Duration,
+    /// Queue strategy (FIFO or LIFO)
+    pub(crate) queue_strategy: QueueStrategy,
     /// User-supplied trait object responsible for initializing connections
     pub(crate) connection_customizer: Option<Box<dyn CustomizeConnection<M::Connection, M::Error>>>,
     _p: PhantomData<M>,
@@ -112,6 +122,7 @@ impl<M: ManageConnection> Default for Builder<M> {
             retry_connection: true,
             error_sink: Box::new(NopErrorSink),
             reaper_rate: Duration::from_secs(30),
+            queue_strategy: QueueStrategy::FIFO,
             connection_customizer: None,
             _p: PhantomData,
         }
@@ -260,6 +271,15 @@ impl<M: ManageConnection> Builder<M> {
         self
     }
 
+    /// Sets the queue strategy to be used by the pool
+    ///
+    /// Defaults to `LIFO`.
+    #[must_use]
+    pub fn queue_strategy(mut self, queue_strategy: QueueStrategy) -> Self {
+        self.queue_strategy = queue_strategy;
+        self
+    }
+
     /// Set the connection customizer to customize newly checked out connections
     #[must_use]
     pub fn connection_customizer(
diff --git a/bb8/src/internals.rs b/bb8/src/internals.rs
index cffd928..0050a67 100644
--- a/bb8/src/internals.rs
+++ b/bb8/src/internals.rs
@@ -2,7 +2,7 @@ use std::cmp::min;
 use std::sync::Arc;
 use std::time::Instant;
 
-use crate::lock::Mutex;
+use crate::{lock::Mutex, api::QueueStrategy};
 use futures_channel::oneshot;
 
 use crate::api::{Builder, ManageConnection};
@@ -42,6 +42,7 @@ where
     conns: VecDeque<IdleConn<M::Connection>>,
     num_conns: u32,
     pending_conns: u32,
+    queue_strategy: QueueStrategy,
 }
 
 impl<M> PoolInternals<M>
@@ -80,8 +81,14 @@ where
         }
 
         // Queue it in the idle queue
-        self.conns
-            .push_back(IdleConn::from(guard.conn.take().unwrap()));
+        match self.queue_strategy {
+            QueueStrategy::FIFO => self
+                .conns
+                .push_back(IdleConn::from(guard.conn.take().unwrap())),
+            QueueStrategy::LIFO => self
+                .conns
+                .push_front(IdleConn::from(guard.conn.take().unwrap())),
+        }
     }
 
     pub(crate) fn connect_failed(&mut self, _: Approval) {
@@ -163,6 +170,7 @@ where
             conns: VecDeque::new(),
             num_conns: 0,
             pending_conns: 0,
+            queue_strategy: QueueStrategy::LIFO,
         }
     }
 }

From 178012242aa6160d8a6589fdc7a00159987ac1aa Mon Sep 17 00:00:00 2001
From: Zain Kabani <zain.kabani@instacart.com>
Date: Wed, 24 May 2023 13:40:34 -0400
Subject: [PATCH 2/2] Fix comment and fmt

---
 bb8/src/api.rs       | 2 +-
 bb8/src/internals.rs | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/bb8/src/api.rs b/bb8/src/api.rs
index 6dc8219..e1a72fe 100644
--- a/bb8/src/api.rs
+++ b/bb8/src/api.rs
@@ -273,7 +273,7 @@ impl<M: ManageConnection> Builder<M> {
 
     /// Sets the queue strategy to be used by the pool
     ///
-    /// Defaults to `LIFO`.
+    /// Defaults to `FIFO`.
     #[must_use]
     pub fn queue_strategy(mut self, queue_strategy: QueueStrategy) -> Self {
         self.queue_strategy = queue_strategy;
diff --git a/bb8/src/internals.rs b/bb8/src/internals.rs
index 0050a67..1ec3e42 100644
--- a/bb8/src/internals.rs
+++ b/bb8/src/internals.rs
@@ -2,7 +2,7 @@ use std::cmp::min;
 use std::sync::Arc;
 use std::time::Instant;
 
-use crate::{lock::Mutex, api::QueueStrategy};
+use crate::{api::QueueStrategy, lock::Mutex};
 use futures_channel::oneshot;
 
 use crate::api::{Builder, ManageConnection};