Make schema version access (but not modification) thread-safe

Also cache the version in statements so that we don't have to lock
the mutex (slow) every time we need to check the version.

3 files changed, 33 insertions, 5 deletions

diff --git a/odb/mysql/section-statements.hxx b/odb/mysql/section-statements.hxx
index 2e01df4..bc83942 100644
--- a/odb/mysql/section-statements.hxx
+++ b/odb/mysql/section-statements.hxx
@@ -10,12 +10,15 @@
 #include <cstddef> // std::size_t
 
 #include <odb/forward.hxx>
+#include <odb/schema-version.hxx>
 #include <odb/traits.hxx>
 
 #include <odb/mysql/version.hxx>
 #include <odb/mysql/mysql.hxx>
 #include <odb/mysql/binding.hxx>
 #include <odb/mysql/statement.hxx>
+#include <odb/mysql/connection.hxx>
+#include <odb/mysql/database.hxx>
 #include <odb/mysql/details/export.hxx>
 
 namespace odb
@@ -46,6 +49,15 @@ namespace odb
       connection_type&
       connection () {return conn_;}
 
+      const schema_version_migration&
+      version_migration (const char* name = "") const
+      {
+        if (svm_ == 0)
+          svm_ = &conn_.database ().schema_version_migration (name);
+
+        return *svm_;
+      }
+
       image_type&
       image () {return image_;}
 
@@ -140,6 +152,7 @@ namespace odb
 
     protected:
       connection_type& conn_;
+      mutable const schema_version_migration* svm_;
 
       // These come from object_statements.
       //
diff --git a/odb/mysql/section-statements.txx b/odb/mysql/section-statements.txx
index 282551c..9bb8689 100644
--- a/odb/mysql/section-statements.txx
+++ b/odb/mysql/section-statements.txx
@@ -14,6 +14,7 @@ namespace odb
                         image_type& im,
                         binding& id, binding& idv)
         : conn_ (conn),
+          svm_ (0),
           image_ (im),
           id_binding_ (id),
           idv_binding_ (idv),
diff --git a/odb/mysql/statements-base.hxx b/odb/mysql/statements-base.hxx
index c0630ef..09d4789 100644
--- a/odb/mysql/statements-base.hxx
+++ b/odb/mysql/statements-base.hxx
@@ -7,10 +7,12 @@
 
 #include <odb/pre.hxx>
 
+#include <odb/schema-version.hxx>
 #include <odb/details/shared-ptr.hxx>
 
 #include <odb/mysql/version.hxx>
-#include <odb/mysql/forward.hxx> // connection
+#include <odb/mysql/connection.hxx>
+#include <odb/mysql/database.hxx>
 
 #include <odb/mysql/details/export.hxx>
 
@@ -29,18 +31,30 @@ namespace odb
         return conn_;
       }
 
+      // Schema version. database::schema_version_migration() is thread-
+      // safe which means it is also slow. Cache the result in statements
+      // so we can avoid the mutex lock. This is thread-safe since if the
+      // version is updated, then the statements cache will be expired.
+      //
+      const schema_version_migration&
+      version_migration (const char* name = "") const
+      {
+        if (svm_ == 0)
+          svm_ = &conn_.database ().schema_version_migration (name);
+
+        return *svm_;
+      }
+
     public:
       virtual
       ~statements_base ();
 
     protected:
-      statements_base (connection_type& conn)
-        : conn_ (conn)
-      {
-      }
+      statements_base (connection_type& conn): conn_ (conn), svm_ (0) {}
 
     protected:
       connection_type& conn_;
+      mutable const schema_version_migration* svm_;
     };
   }
 }