Isolate tests by running AtExit callbacks between them.

base/lazy_instance.cc

 // Copyright (c) 2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/lazy_instance.h"
 
 #include "base/at_exit.h"
 #include "base/atomicops.h"
 #include "base/dynamic_annotations.h"
 #include "base/basictypes.h"
 #include "base/platform_thread.h"
 
 namespace base {
 
 void LazyInstanceHelper::EnsureInstance(void* instance,
                                         void (*ctor)(void*),
                                         void (*dtor)(void*)) {
   // Try to create the instance, if we're the first, will go from EMPTY
   // to CREATING, otherwise we've already been beaten here.
   if (base::subtle::Acquire_CompareAndSwap(
           &state_, STATE_EMPTY, STATE_CREATING) == STATE_EMPTY) {
     // Created the instance in the space provided by |instance|.
     ctor(instance);
 
     // See the comment to the corresponding HAPPENS_AFTER in Pointer().
     ANNOTATE_HAPPENS_BEFORE(&state_);
 
     // Instance is created, go from CREATING to CREATED.
     base::subtle::Release_Store(&state_, STATE_CREATED);
-    // Register the destructor callback with AtExitManager.
+
+    // Allow reusing the LazyInstance (reset it to the initial state). This
+    // makes possible calling all AtExit callbacks between tests. Assumes that
+    // no other threads execute when AtExit callbacks are processed.
+    base::AtExitManager::RegisterCallback(&LazyInstanceHelper::ResetState,
+                                          this);
+
+    // Make sure that the lazily instantiated object will get destroyed at exit.
     base::AtExitManager::RegisterCallback(dtor, instance);
   } else {
     // It's either in the process of being created, or already created.  Spin.
     while (base::subtle::NoBarrier_Load(&state_) != STATE_CREATED)
       PlatformThread::YieldCurrentThread();
   }
 }
 
+// static
+void LazyInstanceHelper::ResetState(void* helper) {
+  reinterpret_cast<LazyInstanceHelper*>(helper)->state_ = STATE_EMPTY;
+}
+
 }  // namespace base