IndexedDB: Remove transaction timer, just post tasks

In the Blink implementation transactions used a timer to
keep to schedule asynchronous processing of tasks. This
was retained in the Chromium port, but with access to the
message loop we can post tasks instead.

Note that transactions still maintain an internal list of
tasks and all that is posted is a "process the queue" task.
Future changes may integrate the transaction task queue and
the message loop more tightly.

BUG=246629

Review URL: https://chromiumcodereview.appspot.com/18612007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@210969 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 27 insertions, 19 deletions

diff --git a/content/browser/indexed_db/indexed_db_transaction.cc b/content/browser/indexed_db/indexed_db_transaction.cc
index cdfb133..19b2b28 100644
--- a/content/browser/indexed_db/indexed_db_transaction.cc
+++ b/content/browser/indexed_db/indexed_db_transaction.cc
@@ -4,7 +4,9 @@
 
 #include "content/browser/indexed_db/indexed_db_transaction.h"
 
+#include "base/bind.h"
 #include "base/logging.h"
+#include "base/message_loop/message_loop.h"
 #include "base/strings/utf_string_conversions.h"
 #include "content/browser/indexed_db/indexed_db_backing_store.h"
 #include "content/browser/indexed_db/indexed_db_cursor.h"
@@ -76,6 +78,7 @@ IndexedDBTransaction::IndexedDBTransaction(
       callbacks_(callbacks),
       database_(database),
       transaction_(database->BackingStore().get()),
+      should_process_queue_(false),
       pending_preemptive_events_(0) {
   database_->transaction_coordinator().DidCreateTransaction(this);
 }
@@ -103,13 +106,14 @@ void IndexedDBTransaction::ScheduleTask(IndexedDBDatabase::TaskType type,
   if (abort_task)
     abort_task_stack_.push(abort_task);
 
-  if (state_ == UNUSED)
+  if (state_ == UNUSED) {
     Start();
-  else if (state_ == RUNNING && !task_timer_.IsRunning())
-    task_timer_.Start(FROM_HERE,
-                      base::TimeDelta::FromSeconds(0),
-                      this,
-                      &IndexedDBTransaction::TaskTimerFired);
+  } else if (state_ == RUNNING && !should_process_queue_) {
+    should_process_queue_ = true;
+    base::MessageLoop::current()->PostTask(
+        FROM_HERE,
+        base::Bind(&IndexedDBTransaction::ProcessTaskQueue, this));
+  }
 }
 
 void IndexedDBTransaction::Abort() {
@@ -130,7 +134,7 @@ void IndexedDBTransaction::Abort(const IndexedDBDatabaseError& error) {
   scoped_refptr<IndexedDBTransaction> protect(this);
 
   state_ = FINISHED;
-  task_timer_.Stop();
+  should_process_queue_ = false;
 
   if (was_running)
     transaction_.Rollback();
@@ -184,15 +188,14 @@ void IndexedDBTransaction::UnregisterOpenCursor(IndexedDBCursor* cursor) {
 }
 
 void IndexedDBTransaction::Run() {
-  // TransactionCoordinator has started this transaction. Schedule a timer
-  // to process the first task.
+  // TransactionCoordinator has started this transaction.
   DCHECK(state_ == START_PENDING || state_ == RUNNING);
-  DCHECK(!task_timer_.IsRunning());
+  DCHECK(!should_process_queue_);
 
-  task_timer_.Start(FROM_HERE,
-                    base::TimeDelta::FromSeconds(0),
-                    this,
-                    &IndexedDBTransaction::TaskTimerFired);
+  should_process_queue_ = true;
+  base::MessageLoop::current()->PostTask(
+      FROM_HERE,
+      base::Bind(&IndexedDBTransaction::ProcessTaskQueue, this));
 }
 
 void IndexedDBTransaction::Start() {
@@ -261,9 +264,15 @@ void IndexedDBTransaction::Commit() {
   database_ = NULL;
 }
 
-void IndexedDBTransaction::TaskTimerFired() {
-  IDB_TRACE("IndexedDBTransaction::TaskTimerFired");
+void IndexedDBTransaction::ProcessTaskQueue() {
+  IDB_TRACE("IndexedDBTransaction::ProcessTaskQueue");
+
+  // May have been aborted.
+  if (!should_process_queue_)
+    return;
+
   DCHECK(!IsTaskQueueEmpty());
+  should_process_queue_ = false;
 
   if (state_ == START_PENDING) {
     transaction_.Begin();
diff --git a/content/browser/indexed_db/indexed_db_transaction.h b/content/browser/indexed_db/indexed_db_transaction.h
index c1a20d5..70160e1 100644
--- a/content/browser/indexed_db/indexed_db_transaction.h
+++ b/content/browser/indexed_db/indexed_db_transaction.h
@@ -13,7 +13,6 @@
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/timer/timer.h"
 #include "content/browser/indexed_db/indexed_db_backing_store.h"
 #include "content/browser/indexed_db/indexed_db_database.h"
 #include "content/browser/indexed_db/indexed_db_database_error.h"
@@ -97,7 +96,7 @@ class IndexedDBTransaction : public base::RefCounted<IndexedDBTransaction> {
   bool IsTaskQueueEmpty() const;
   bool HasPendingTasks() const;
 
-  void TaskTimerFired();
+  void ProcessTaskQueue();
   void CloseOpenCursors();
 
   const int64 id_;
@@ -141,7 +140,7 @@ class IndexedDBTransaction : public base::RefCounted<IndexedDBTransaction> {
 
   IndexedDBBackingStore::Transaction transaction_;
 
-  base::OneShotTimer<IndexedDBTransaction> task_timer_;
+  bool should_process_queue_;
   int pending_preemptive_events_;
 
   std::set<IndexedDBCursor*> open_cursors_;