From 31789cec4f59f7a6fd1e92eac523c595a7b102ac Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Sat, 28 Sep 2013 10:51:12 +0200
Subject: 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.
---
 odb/pgsql/statements-base.hxx | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

(limited to 'odb/pgsql/statements-base.hxx')

diff --git a/odb/pgsql/statements-base.hxx b/odb/pgsql/statements-base.hxx
index 9647984..efb5753 100644
--- a/odb/pgsql/statements-base.hxx
+++ b/odb/pgsql/statements-base.hxx
@@ -7,10 +7,12 @@
 
 #include <odb/pre.hxx>
 
+#include <odb/schema-version.hxx>
 #include <odb/details/shared-ptr.hxx>
 
 #include <odb/pgsql/version.hxx>
-#include <odb/pgsql/forward.hxx> // connection
+#include <odb/pgsql/connection.hxx>
+#include <odb/pgsql/database.hxx>
 
 #include <odb/pgsql/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_;
     };
   }
 }
-- 
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