Changeset 65361 in vbox for trunk/src/VBox/Main

Timestamp:

Jan 18, 2017 1:14:05 PM (8 years ago)

Author:

vboxsync

Message:

xpcom/server.cpp: use a guaranteed safe sequence (never decreasing the refcount speculatively) for figuring out if some API client is racing against the 5 seconds idle timeout

File:

• trunk/src/VBox/Main/src-server/xpcom/server.cpp (modified) (5 diffs)

trunk/src/VBox/Main/src-server/xpcom/server.cpp

@@ -5 +5 @@
 
 /*
- * Copyright (C) 2004-2016 Oracle Corporation
+ * Copyright (C) 2004-2017 Oracle Corporation
  *
  * This file is part of VirtualBox Open Source Edition (OSE), as
@@ -234 +234 @@
             RTCritSectEnter(&sLock);
 
-            nsrefcnt count = 0;
+            nsrefcnt count = 1;
 
             /* sInstance is NULL here if it was deleted immediately after
@@ -240 +240 @@
             if (sInstance != NULL)
             {
-                /* Release the guard reference added in GetInstance() */
+                /* Safe way to get current refcount is by first increasing and
+                 * then decreasing. Keep in mind that the Release is overloaded
+                 * (see VirtualBoxClassFactory::Release) and will start the
+                 * timer again if the returned count is 1. It won't do harm,
+                 * but also serves no purpose, so stop it ASAP. */
+                sInstance->AddRef();
                 count = sInstance->Release();
-            }
-
-            if (count == 0)
+                if (count == 1)
+                {
+                    RTTimerLRStop(sTimer);
+                    /* Release the guard reference added in GetInstance() */
+                    sInstance->Release();
+                }
+            }
+
+            if (count == 1)
             {
                 if (gAutoShutdown || m_fSignal)
@@ -262 +273 @@
                  * but before it started to process it. */
                 LogRel(("Destruction is canceled (refcnt=%d).\n", count));
-                /* Important: restore previous refcount, we decreased it
-                 * above based on the assumption that the object is unused! */
-                sInstance->AddRef();
             }
 
@@ -408 +416 @@
             Assert(count > 1);
 
-            if (count == 2)
+            if (count >= 2)
             {
                 LogFlowFunc(("Another client has requested a reference to VirtualBox, canceling destruction...\n"));