[IndexedDB] Transaction limitting

content/browser/indexed_db/indexed_db_transaction_coordinator.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/indexed_db/indexed_db_transaction_coordinator.h"
 
 #include "base/logging.h"
 #include "content/browser/indexed_db/indexed_db_transaction.h"
 #include "third_party/WebKit/public/platform/modules/indexeddb/WebIDBTypes.h"
 
 namespace content {
+namespace {
+
+// Only this many transactions can be active at any time before they are queued.
+// Limited to prevent transaction trashing which can consume a ton of RAM. Ten
+// is chosen to reduce performance regressions.
+// TODO(dmurph): crbug.com/693260 Create better scheduling or limits.
+static const size_t kMaxStartedTransactions = 10;
+
+}  // namespace
 
 IndexedDBTransactionCoordinator::IndexedDBTransactionCoordinator() {}
 
 IndexedDBTransactionCoordinator::~IndexedDBTransactionCoordinator() {
   DCHECK(queued_transactions_.empty());
   DCHECK(started_transactions_.empty());
 }
 
 void IndexedDBTransactionCoordinator::DidCreateTransaction(
     IndexedDBTransaction* transaction) {
@@ skipping 117 matching lines @@
       ++it2;
     else
       return true;
   }
   return false;
 }
 
 bool IndexedDBTransactionCoordinator::CanStartTransaction(
     IndexedDBTransaction* const transaction,
     const std::set<int64_t>& locked_scope) const {
+  if (started_transactions_.size() >= kMaxStartedTransactions) {
+    return false;
+  }
   DCHECK(queued_transactions_.count(transaction));
   switch (transaction->mode()) {
     case blink::WebIDBTransactionModeVersionChange:
       DCHECK_EQ(1u, queued_transactions_.size());
       DCHECK(started_transactions_.empty());
       DCHECK(locked_scope.empty());
       return true;
 
     case blink::WebIDBTransactionModeReadOnly:
     case blink::WebIDBTransactionModeReadWrite:
       return !DoSetsIntersect(transaction->scope(), locked_scope);
   }
   NOTREACHED();
   return false;
 }
 
 }  // namespace content