Attempt to fix a DCHECK failure related to usage of Singletons

and WorkerPool.

Also add a warning for users of WorkerPool that they need to be
very careful about subtle issues.

Also see discussion in http://codereview.chromium.org/1834002/show

TEST=none
BUG=30177

Review URL: http://codereview.chromium.org/2033001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@46665 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 6 insertions, 7 deletions

diff --git a/net/base/host_resolver_impl.cc b/net/base/host_resolver_impl.cc
index 1c97f22..f901144 100644
--- a/net/base/host_resolver_impl.cc
+++ b/net/base/host_resolver_impl.cc
@@ -316,6 +316,10 @@ class HostResolverImpl::Job
     STLDeleteElements(&requests_);
   }
 
+  // WARNING: This code runs inside a worker pool. The shutdown code cannot
+  // wait for it to finish, so we must be very careful here about using other
+  // objects (like MessageLoops, Singletons, etc). During shutdown these objects
+  // may no longer exist.
   void DoLookup() {
     if (requests_trace_) {
       requests_trace_->Add(StringPrintf(
@@ -334,20 +338,15 @@ class HostResolverImpl::Job
           "[resolver thread] Completed job j%d", id_));
     }
 
-    Task* reply = NewRunnableMethod(this, &Job::OnLookupComplete);
-
     // The origin loop could go away while we are trying to post to it, so we
     // need to call its PostTask method inside a lock.  See ~HostResolver.
     {
       AutoLock locked(origin_loop_lock_);
       if (origin_loop_) {
-        origin_loop_->PostTask(FROM_HERE, reply);
-        reply = NULL;
+        origin_loop_->PostTask(FROM_HERE,
+                               NewRunnableMethod(this, &Job::OnLookupComplete));
       }
     }
-
-    // Does nothing if it got posted.
-    delete reply;
   }
 
   // Callback for when DoLookup() completes (runs on origin thread).