Don't use async/await for Pool.withResource(). The async gap introduces a potential race condition. Closes dart-lang/pool#3 R=rnystrom@google.com Review URL: https://codereview.chromium.org//1853273002 .

diff --git a/pkgs/pool/CHANGELOG.md b/pkgs/pool/CHANGELOG.md
index 9ad86d0..70f914b 100644
--- a/pkgs/pool/CHANGELOG.md
+++ b/pkgs/pool/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 1.2.3
+
+* Fix a bug in which `Pool.withResource()` could throw a `StateError` when
+  called immediately before closing the pool.
+
 ## 1.2.2
 
 * Fix strong mode warnings and add generic method annotations.

diff --git a/pkgs/pool/lib/pool.dart b/pkgs/pool/lib/pool.dart
index f7bfd82..deb5333 100644
--- a/pkgs/pool/lib/pool.dart
+++ b/pkgs/pool/lib/pool.dart

@@ -106,18 +106,19 @@
   /// Future.
   ///
   /// The return value of [callback] is piped to the returned Future.
-  Future/*<T>*/ withResource/*<T>*/(/*=T*/ callback()) async {
+  Future/*<T>*/ withResource/*<T>*/(/*=T*/ callback()) {
     if (isClosed) {
       throw new StateError(
           "withResource() may not be called on a closed Pool.");
     }
 
-    var resource = await request();
-    try {
-      return await callback();
-    } finally {
-      resource.release();
-    }
+    // We can't use async/await here because we need to start the request
+    // synchronously in case the pool is closed immediately afterwards. Async
+    // functions have an asynchronous gap between calling and running the body,
+    // and [close] could be called during that gap. See #3.
+    return request().then((resource) {
+      return new Future.sync(callback).whenComplete(resource.release);
+    });
   }
 
   /// Closes the pool so that no more resources are requested.

diff --git a/pkgs/pool/pubspec.yaml b/pkgs/pool/pubspec.yaml
index 314ac04..58321cf 100644
--- a/pkgs/pool/pubspec.yaml
+++ b/pkgs/pool/pubspec.yaml

@@ -1,5 +1,5 @@
 name: pool
-version: 1.2.2
+version: 1.2.3
 author: Dart Team <misc@dartlang.org>
 description: A class for managing a finite pool of resources.
 homepage: https://github.com/dart-lang/pool

diff --git a/pkgs/pool/test/pool_test.dart b/pkgs/pool/test/pool_test.dart
index 91e6833..bd44cb2 100644
--- a/pkgs/pool/test/pool_test.dart
+++ b/pkgs/pool/test/pool_test.dart

@@ -96,6 +96,13 @@
         async.elapse(new Duration(seconds: 1));
       });
     });
+
+    // Regression test for #3.
+    test("can be called immediately before close()", () async {
+      var pool = new Pool(1);
+      pool.withResource(expectAsync(() {}));
+      await pool.close();
+    });
   });
 
   group("with a timeout", () {
@@ -276,7 +283,7 @@
     test("disallows request() and withResource()", () {
       var pool = new Pool(1)..close();
       expect(pool.request, throwsStateError);
-      expect(pool.withResource(() {}), throwsStateError);
+      expect(() => pool.withResource(() {}), throwsStateError);
     });
 
     test("pending requests are fulfilled", () async {