fix(pools): release the reserved slot when connection creation fails

packages/pools/src/Pools/Pool.php

@@ -376,19 +376,28 @@ public function pop(): Connection
                 });
 
                 if ($shouldCreateConnections) {
+                    $reserved = true;
+
                     try {
                         $connection = $this->createConnection();
                         $this->pool->synchronized(function () use ($connection): void {
                             $this->active[$connection->getID()] = $connection;
                         });
+                        $reserved = false;
+
                         return $connection;
-                    } catch (\Exception $e) {
-                        $this->pool->synchronized(function (): void {
-                            $this->connectionsCreated--;
-                        });
+                    } catch (\Throwable $e) {
+                        // Throwable, not Exception: the init callback is caller
+                        // supplied, so an Error holds the slot just the same.
                         // Don't throw immediately - fall through to try getting
                         // an existing connection from the pool
                         $lastException = $e;
+                    } finally {
+                        if ($reserved) {
+                            $this->pool->synchronized(function (): void {
+                                $this->connectionsCreated--;
+                            });
+                        }
                     }
                 }
 

packages/pools/tests/Pools/Scopes/PoolTestScope.php

@@ -341,6 +341,35 @@ public function testPopRetriesAfterConnectionCreationFailure(): void
         });
     }
 
+    public function testPopReleasesReservedSlotWhenCreationThrowsError(): void
+    {
+        $this->execute(function (): void {
+            // pop() reserves capacity before the connection exists. An Error
+            // escaping the catch used to keep that slot, draining the pool one
+            // failed pop at a time.
+            $pool = new Pool($this->getAdapter(), 'test-error-leak', 2, function (): string {
+                throw new \TypeError('Connection init failed');
+            });
+            $pool->setReconnectAttempts(1);
+            $pool->setReconnectSleep(0);
+            $pool->setRetryAttempts(1);
+            $pool->setRetrySleep(0);
+
+            // More attempts than slots, so a kept reservation shows up as lost
+            // capacity by the end.
+            for ($i = 0; $i < 5; $i++) {
+                try {
+                    $pool->pop();
+                    $this->fail('Should have thrown');
+                } catch (Exception $e) {
+                    $this->assertInstanceOf(\TypeError::class, $e->getPrevious());
+                }
+            }
+
+            $this->assertSame(2, $pool->count());
+        });
+    }
+
     public function testPoolEmptyErrorIncludesActiveCount(): void
     {
         $this->execute(function (): void {