Relax check for message loop in SequencedWorkerPool

Assert that the constructor message loop is non-NULL only when
the SequencedWorkerPool is about to be destroyed.

Revert now-unneccessary test changes that adds MessagePools for
SequenedWorkerPool.

BUG=117940
TEST=


Review URL: http://codereview.chromium.org/9699115

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@127335 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 12 insertions, 9 deletions

diff --git a/base/threading/sequenced_worker_pool.cc b/base/threading/sequenced_worker_pool.cc
index d517d21..d994d97 100644
--- a/base/threading/sequenced_worker_pool.cc
+++ b/base/threading/sequenced_worker_pool.cc
@@ -692,7 +692,6 @@ SequencedWorkerPool::SequencedWorkerPool(
     : constructor_message_loop_(MessageLoopProxy::current()),
       inner_(new Inner(ALLOW_THIS_IN_INITIALIZER_LIST(this),
                        max_threads, thread_name_prefix, NULL)) {
-  DCHECK(constructor_message_loop_.get());
 }
 
 SequencedWorkerPool::SequencedWorkerPool(
@@ -702,19 +701,19 @@ SequencedWorkerPool::SequencedWorkerPool(
     : constructor_message_loop_(MessageLoopProxy::current()),
       inner_(new Inner(ALLOW_THIS_IN_INITIALIZER_LIST(this),
                        max_threads, thread_name_prefix, observer)) {
-  DCHECK(constructor_message_loop_.get());
 }
 
 SequencedWorkerPool::~SequencedWorkerPool() {}
 
 void SequencedWorkerPool::OnDestruct() const {
-  // TODO(akalin): Once we can easily check if we're on a worker
-  // thread or not, use that instead of restricting destruction to
-  // only the constructor message loop.
-  if (constructor_message_loop_->BelongsToCurrentThread())
-    delete this;
-  else
+  DCHECK(constructor_message_loop_.get());
+  // Avoid deleting ourselves on a worker thread (which would
+  // deadlock).
+  if (RunsTasksOnCurrentThread()) {
     constructor_message_loop_->DeleteSoon(FROM_HERE, this);
+  } else {
+    delete this;
+  }
 }
 
 SequencedWorkerPool::SequenceToken SequencedWorkerPool::GetSequenceToken() {
diff --git a/base/threading/sequenced_worker_pool.h b/base/threading/sequenced_worker_pool.h
index ded2b0a..83d677a 100644
--- a/base/threading/sequenced_worker_pool.h
+++ b/base/threading/sequenced_worker_pool.h
@@ -127,8 +127,12 @@ class BASE_EXPORT SequencedWorkerPool : public TaskRunner {
     virtual void OnDestruct() = 0;
   };
 
+  // When constructing a SequencedWorkerPool, there must be a
+  // MessageLoop on the current thread unless you plan to deliberately
+  // leak it.
+
   // Pass the maximum number of threads (they will be lazily created as needed)
-  // and a prefix for the thread name to ad in debugging.
+  // and a prefix for the thread name to aid in debugging.
   SequencedWorkerPool(size_t max_threads,
                       const std::string& thread_name_prefix);