From 26cd25c14be177320a5914e51e4f0775b344dc05 Mon Sep 17 00:00:00 2001
From: Michael Tharp <michael.tharp@sas.com>
Date: Mon, 16 Dec 2019 21:52:20 +0000
Subject: [PATCH 1/2] Fix deadlock race when acquire is cancelled

If the waiter goroutine completes before the section guarding
canceledAcquireCount has run, then there is a deadlock because there is
nothing that can unlock the mutex. Scheduling the second goroutine
ensures that one of the two can release the lock and keep things moving.
---
 pool.go | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/pool.go b/pool.go
index 2bce46c..5f57feb 100644
--- a/pool.go
+++ b/pool.go
@@ -303,10 +303,6 @@ func (p *Pool) Acquire(ctx context.Context) (*Resource, error) {
 
 			select {
 			case <-ctx.Done():
-				p.cond.L.Lock()
-				p.canceledAcquireCount += 1
-				p.cond.L.Unlock()
-
 				// Allow goroutine waiting for signal to exit. Re-signal since we couldn't
 				// do anything with it. Another goroutine might be waiting.
 				go func() {
@@ -315,6 +311,9 @@ func (p *Pool) Acquire(ctx context.Context) (*Resource, error) {
 					p.cond.L.Unlock()
 				}()
 
+				p.cond.L.Lock()
+				p.canceledAcquireCount += 1
+				p.cond.L.Unlock()
 				return nil, ctx.Err()
 			case <-waitChan:
 			}

From f458c9c0f8e3b37d14f94f75b574cc9198a27163 Mon Sep 17 00:00:00 2001
From: Jack Christensen <jack@jackchristensen.com>
Date: Sat, 25 Jan 2020 16:17:17 -0600
Subject: [PATCH 2/2] Make stress test more stressful

Detect bug fixed by 26cd25c14be177320a5914e51e4f0775b344dc05. See also
https://github.com/jackc/puddle/pull/2.
---
 pool_test.go | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/pool_test.go b/pool_test.go
index 837e546..7ce41e9 100644
--- a/pool_test.go
+++ b/pool_test.go
@@ -8,6 +8,7 @@ import (
 	"math/rand"
 	"net"
 	"os"
+	"runtime"
 	"sync"
 	"testing"
 	"time"
@@ -514,7 +515,12 @@ func TestStress(t *testing.T) {
 		destructorCalls.Next()
 	}
 
-	pool := puddle.NewPool(constructor, destructor, 10)
+	poolSize := runtime.NumCPU()
+	if poolSize < 4 {
+		poolSize = 4
+	}
+
+	pool := puddle.NewPool(constructor, destructor, int32(poolSize))
 
 	finishChan := make(chan struct{})
 	wg := &sync.WaitGroup{}
@@ -547,7 +553,7 @@ func TestStress(t *testing.T) {
 		},
 		// Acquire possibly canceled by context
 		func() {
-			ctx, cancel := context.WithTimeout(context.Background(), time.Duration(rand.Int63n(200))*time.Millisecond)
+			ctx, cancel := context.WithTimeout(context.Background(), time.Duration(rand.Int63n(2000))*time.Nanosecond)
 			defer cancel()
 			res, err := pool.Acquire(ctx)
 			if err != nil {
@@ -557,7 +563,7 @@ func TestStress(t *testing.T) {
 				return
 			}
 
-			time.Sleep(time.Duration(rand.Int63n(100)) * time.Millisecond)
+			time.Sleep(time.Duration(rand.Int63n(2000)) * time.Nanosecond)
 			releaseOrDestroyOrHijack(res)
 		},
 		// AcquireAllIdle (though under heavy load this will almost certainly always get an empty slice)
@@ -569,7 +575,9 @@ func TestStress(t *testing.T) {
 		},
 	}
 
-	for i := 0; i < 100; i++ {
+	workerCount := int(poolSize) * 2
+
+	for i := 0; i < workerCount; i++ {
 		wg.Add(1)
 		go func() {
 			for {