Base: Fix another deadlock during shutdown of SequencedWorkerPool.

base/threading/sequenced_worker_pool.cc

Index: base/threading/sequenced_worker_pool.cc
diff --git a/base/threading/sequenced_worker_pool.cc b/base/threading/sequenced_worker_pool.cc
index 19b81b7b4b32a32d58bd74e2f8e237aa082f1722..b6c20337c05d6bbe02454643ca71b474c99e65d9 100644
--- a/base/threading/sequenced_worker_pool.cc
+++ b/base/threading/sequenced_worker_pool.cc
@@ -803,6 +803,18 @@ void SequencedWorkerPool::Inner::ThreadLoop(Worker* this_worker) {
           delete_these_outside_lock.clear();
           break;
         }
+
+        // No work was found, but there are tasks that need deletion. The
+        // deletion must happen outside of the lock. Since the lock has been

[brettw, 2015/03/12 23:12:42]

I don't follow this, maybe the comment needs to be clarified.

This talks about the lock "has been released" but when this code is called, the
lock is still held.

[erikchen, 2015/03/12 23:24:52]

I broke the comment in two, moved the location of the second comment, and
rewrote it to be more precise. I've reproduced it here for your convenience:

 // Since the lock has been released, |status| may no longer be
 // accurate. It might read GET_WORK_WAIT even if there are tasks
 // ready to perform work. Jump to the top of the loop to recalculate
 // |status|.

+        // released, the current state about whether there is more work is no
+        // longer valid, and needs to be recalculated by jumping to the top of
+        // the loop.
+        if (delete_these_outside_lock.size()) {
+          AutoUnlock unlock(lock_);
+          delete_these_outside_lock.clear();
+          continue;
+        }
+
         waiting_thread_count_++;
 
         switch (status) {