Add support for transaction multiplexing

Also delay getting a connection until after we do all the sanity
checks (e.g., that there is no active transaction). Otherwise we
are running risk of getting blocked rather than throwing an
exception.

8 files changed, 47 insertions, 19 deletions

diff --git a/odb/pgsql/connection.cxx b/odb/pgsql/connection.cxx
index 808cdbb..0a23ed7 100644
--- a/odb/pgsql/connection.cxx
+++ b/odb/pgsql/connection.cxx
@@ -73,9 +73,6 @@ namespace odb
     transaction_impl* connection::
     begin ()
     {
-      if (transaction::has_current ())
-        throw already_in_transaction ();
-
       return new transaction_impl (connection_ptr (inc_ref (this)));
     }
 
diff --git a/odb/pgsql/database.cxx b/odb/pgsql/database.cxx
index 050961f..8d8b797 100644
--- a/odb/pgsql/database.cxx
+++ b/odb/pgsql/database.cxx
@@ -208,6 +208,12 @@ namespace odb
     {
     }
 
+    transaction_impl* database::
+    begin ()
+    {
+      return new transaction_impl (*this);
+    }
+
     odb::connection* database::
     connection_ ()
     {
diff --git a/odb/pgsql/database.hxx b/odb/pgsql/database.hxx
index d3d8f7d..1b688fc 100644
--- a/odb/pgsql/database.hxx
+++ b/odb/pgsql/database.hxx
@@ -83,7 +83,7 @@ namespace odb
       // Transactions.
       //
     public:
-      transaction_impl*
+      virtual transaction_impl*
       begin ();
 
     public:
diff --git a/odb/pgsql/database.ixx b/odb/pgsql/database.ixx
index 467f765..527e336 100644
--- a/odb/pgsql/database.ixx
+++ b/odb/pgsql/database.ixx
@@ -16,11 +16,5 @@ namespace odb
       return connection_ptr (
         static_cast<pgsql::connection*> (connection_ ()));
     }
-
-    inline transaction_impl* database::
-    begin ()
-    {
-      return connection ()->begin ();
-    }
   }
 }
diff --git a/odb/pgsql/transaction-impl.cxx b/odb/pgsql/transaction-impl.cxx
index 81aaf08..c3ce31d 100644
--- a/odb/pgsql/transaction-impl.cxx
+++ b/odb/pgsql/transaction-impl.cxx
@@ -19,14 +19,15 @@ namespace odb
   namespace pgsql
   {
     transaction_impl::
+    transaction_impl (database_type& db)
+        : odb::transaction_impl (db)
+    {
+    }
+
+    transaction_impl::
     transaction_impl (connection_ptr c)
         : odb::transaction_impl (c->database (), *c), connection_ (c)
     {
-      result_ptr r (PQexec (connection_->handle (), "begin"));
-      PGresult* h (r.get ());
-
-      if (!h || PGRES_COMMAND_OK != PQresultStatus (h))
-        translate_error (*connection_, h);
     }
 
     transaction_impl::
@@ -35,6 +36,24 @@ namespace odb
     }
 
     void transaction_impl::
+    start ()
+    {
+      // Grab a connection if we don't already have one.
+      //
+      if (connection_ == 0)
+      {
+        connection_ = static_cast<database_type&> (database_).connection ();
+        odb::transaction_impl::connection_ = connection_.get ();
+      }
+
+      result_ptr r (PQexec (connection_->handle (), "begin"));
+      PGresult* h (r.get ());
+
+      if (!h || PGRES_COMMAND_OK != PQresultStatus (h))
+        translate_error (*connection_, h);
+    }
+
+    void transaction_impl::
     commit ()
     {
       result_ptr r (PQexec (connection_->handle (), "commit"));
diff --git a/odb/pgsql/transaction-impl.hxx b/odb/pgsql/transaction-impl.hxx
index d3a76ce..2551994 100644
--- a/odb/pgsql/transaction-impl.hxx
+++ b/odb/pgsql/transaction-impl.hxx
@@ -23,19 +23,20 @@ namespace odb
   {
     class LIBODB_PGSQL_EXPORT transaction_impl: public odb::transaction_impl
     {
-    protected:
-      friend class connection;
-      friend class transaction;
-
+    public:
       typedef pgsql::database database_type;
       typedef pgsql::connection connection_type;
 
+      transaction_impl (database_type&);
       transaction_impl (connection_ptr);
 
       virtual
       ~transaction_impl ();
 
       virtual void
+      start ();
+
+      virtual void
       commit ();
 
       virtual void
diff --git a/odb/pgsql/transaction.hxx b/odb/pgsql/transaction.hxx
index 450842d..39675d8 100644
--- a/odb/pgsql/transaction.hxx
+++ b/odb/pgsql/transaction.hxx
@@ -46,6 +46,11 @@ namespace odb
       static transaction&
       current ();
 
+      // Set the current thread's transaction.
+      //
+      static void
+      current (transaction&);
+
     public:
       transaction_impl&
       implementation ();
diff --git a/odb/pgsql/transaction.ixx b/odb/pgsql/transaction.ixx
index d109e97..42fe778 100644
--- a/odb/pgsql/transaction.ixx
+++ b/odb/pgsql/transaction.ixx
@@ -37,5 +37,11 @@ namespace odb
     {
       return implementation ().connection ();
     }
+
+    inline void transaction::
+    current (transaction& t)
+    {
+      odb::transaction::current (t);
+    }
   }
 }