From 79cb2f05559e1ed9e724efd4f5dbceca794e7162 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Thu, 29 Apr 2021 12:37:09 +0200
Subject: Add serial_connection_factory

This factory can be used when the database access is guaranteed to be serial.
---
 odb/sqlite/connection-factory.cxx | 34 ++++++++++++++++++++++++++++++++++
 odb/sqlite/connection-factory.hxx | 37 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 70 insertions(+), 1 deletion(-)

diff --git a/odb/sqlite/connection-factory.cxx b/odb/sqlite/connection-factory.cxx
index 1269db3..1a1f85a 100644
--- a/odb/sqlite/connection-factory.cxx
+++ b/odb/sqlite/connection-factory.cxx
@@ -17,6 +17,40 @@ namespace odb
   namespace sqlite
   {
     //
+    // serial_connection_factory
+    //
+
+    serial_connection_factory::
+    ~serial_connection_factory ()
+    {
+      // We should hold the last reference to the connection.
+      //
+      if (connection_ != 0)
+        assert (connection_.count () == 1);
+    }
+
+    connection_ptr serial_connection_factory::
+    create ()
+    {
+      return connection_ptr (new (shared) connection (*this));
+    }
+
+    connection_ptr serial_connection_factory::
+    connect ()
+    {
+      return connection_;
+    }
+
+    void serial_connection_factory::
+    database (database_type& db)
+    {
+      connection_factory::database (db);
+
+      if (!connection_)
+        connection_ = create ();
+    }
+
+    //
     // single_connection_factory
     //
 
diff --git a/odb/sqlite/connection-factory.hxx b/odb/sqlite/connection-factory.hxx
index b665625..141fff6 100644
--- a/odb/sqlite/connection-factory.hxx
+++ b/odb/sqlite/connection-factory.hxx
@@ -23,7 +23,42 @@ namespace odb
 {
   namespace sqlite
   {
-    // Share a single connection.
+    // Share a single connection in a guaranteed serial database access.
+    //
+    // For example, a single-threaded application that executes all the
+    // operations via the database instance without messing with multiple
+    // connections/transactions would qualify.
+    //
+    class LIBODB_SQLITE_EXPORT serial_connection_factory:
+      public connection_factory
+    {
+    public:
+      serial_connection_factory () {}
+
+      virtual connection_ptr
+      connect ();
+
+      virtual void
+      database (database_type&);
+
+      virtual
+      ~serial_connection_factory ();
+
+    private:
+      serial_connection_factory (const serial_connection_factory&);
+      serial_connection_factory& operator= (const serial_connection_factory&);
+
+    protected:
+      // This function is called when the factory needs to create the
+      // connection.
+      //
+      virtual connection_ptr
+      create ();
+
+      connection_ptr connection_;
+    };
+
+    // Share a single connection potentially between multiple threads.
     //
     class LIBODB_SQLITE_EXPORT single_connection_factory:
       public connection_factory
-- 
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