Create meta table atomically.

http://crbug.com/111376 happened because a crash between creation and
population of the meta table could leave a meta table returning 0 for
the version numbers, even though no client ever stored 0 for the
versions.  This makes creation and population atomic.

Additionally, version numbers are restricted to positive values, to
prevent this case from being masked in the future.

BUG=116306
TEST=none


Review URL: http://codereview.chromium.org/9592026

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@125557 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 17 insertions, 2 deletions

diff --git a/sql/meta_table.cc b/sql/meta_table.cc
index cbda772..45f4ee0 100644
--- a/sql/meta_table.cc
+++ b/sql/meta_table.cc
@@ -8,6 +8,7 @@
 #include "base/string_util.h"
 #include "sql/connection.h"
 #include "sql/statement.h"
+#include "sql/transaction.h"
 
 namespace sql {
 
@@ -30,6 +31,17 @@ bool MetaTable::DoesTableExist(sql::Connection* db) {
 bool MetaTable::Init(Connection* db, int version, int compatible_version) {
   DCHECK(!db_ && db);
   db_ = db;
+
+  // If values stored are null or missing entirely, 0 will be reported.
+  // Require new clients to start with a greater initial version.
+  DCHECK_GT(version, 0);
+  DCHECK_GT(compatible_version, 0);
+
+  // Make sure the table is created an populated atomically.
+  sql::Transaction transaction(db_);
+  if (!transaction.Begin())
+    return false;
+
   if (!DoesTableExist(db)) {
     if (!db_->Execute("CREATE TABLE meta"
         "(key LONGVARCHAR NOT NULL UNIQUE PRIMARY KEY, value LONGVARCHAR)"))
@@ -41,7 +53,7 @@ bool MetaTable::Init(Connection* db, int version, int compatible_version) {
     SetVersionNumber(version);
     SetCompatibleVersionNumber(compatible_version);
   }
-  return true;
+  return transaction.Commit();
 }
 
 void MetaTable::Reset() {
@@ -49,6 +61,7 @@ void MetaTable::Reset() {
 }
 
 void MetaTable::SetVersionNumber(int version) {
+  DCHECK_GT(version, 0);
   SetValue(kVersionKey, version);
 }
 
@@ -58,6 +71,7 @@ int MetaTable::GetVersionNumber() {
 }
 
 void MetaTable::SetCompatibleVersionNumber(int version) {
+  DCHECK_GT(version, 0);
   SetValue(kCompatibleVersionKey, version);
 }
 
diff --git a/sql/meta_table.h b/sql/meta_table.h
index 497d918..03ec705 100644
--- a/sql/meta_table.h
+++ b/sql/meta_table.h
@@ -26,7 +26,8 @@ class SQL_EXPORT MetaTable {
 
   // Initializes the MetaTableHelper, creating the meta table if necessary. For
   // new tables, it will initialize the version number to |version| and the
-  // compatible version number to |compatible_version|.
+  // compatible version number to |compatible_version|.  Versions must be
+  // greater than 0 to distinguish missing versions (see GetVersionNumber()).
   bool Init(Connection* db, int version, int compatible_version);
 
   // Resets this MetaTable object, making another call to Init() possible.