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, 44 insertions, 16 deletions

diff --git a/odb/mysql/connection.cxx b/odb/mysql/connection.cxx
index fe4996f..b783f69 100644
--- a/odb/mysql/connection.cxx
+++ b/odb/mysql/connection.cxx
@@ -77,9 +77,6 @@ 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/mysql/database.cxx b/odb/mysql/database.cxx
index dc78bce..d37351f 100644
--- a/odb/mysql/database.cxx
+++ b/odb/mysql/database.cxx
@@ -208,6 +208,12 @@ namespace odb
       details::options::print_usage (os);
     }
 
+    transaction_impl* database::
+    begin ()
+    {
+      return new transaction_impl (*this);
+    }
+
     odb::connection* database::
     connection_ ()
     {
diff --git a/odb/mysql/database.hxx b/odb/mysql/database.hxx
index 37b966f..ba4ee80 100644
--- a/odb/mysql/database.hxx
+++ b/odb/mysql/database.hxx
@@ -157,7 +157,7 @@ namespace odb
       }
 
     public:
-      transaction_impl*
+      virtual transaction_impl*
       begin ();
 
     public:
diff --git a/odb/mysql/database.ixx b/odb/mysql/database.ixx
index 399fbdc..3c0e6de 100644
--- a/odb/mysql/database.ixx
+++ b/odb/mysql/database.ixx
@@ -16,11 +16,5 @@ namespace odb
       return connection_ptr (
         static_cast<mysql::connection*> (connection_ ()));
     }
-
-    inline transaction_impl* database::
-    begin ()
-    {
-      return connection ()->begin ();
-    }
   }
 }
diff --git a/odb/mysql/transaction-impl.cxx b/odb/mysql/transaction-impl.cxx
index 86cccbe..24c511f 100644
--- a/odb/mysql/transaction-impl.cxx
+++ b/odb/mysql/transaction-impl.cxx
@@ -14,11 +14,15 @@ namespace odb
   namespace mysql
   {
     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)
     {
-      if (mysql_real_query (connection_->handle (), "begin", 5) != 0)
-        translate_error (*connection_);
     }
 
     transaction_impl::
@@ -27,6 +31,21 @@ 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 ();
+      }
+
+      if (mysql_real_query (connection_->handle (), "begin", 5) != 0)
+        translate_error (*connection_);
+    }
+
+    void transaction_impl::
     commit ()
     {
       connection_->clear ();
diff --git a/odb/mysql/transaction-impl.hxx b/odb/mysql/transaction-impl.hxx
index a8aa491..db87147 100644
--- a/odb/mysql/transaction-impl.hxx
+++ b/odb/mysql/transaction-impl.hxx
@@ -23,19 +23,20 @@ namespace odb
   {
     class LIBODB_MYSQL_EXPORT transaction_impl: public odb::transaction_impl
     {
-    protected:
-      friend class connection;
-      friend class transaction;
-
+    public:
       typedef mysql::database database_type;
       typedef mysql::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/mysql/transaction.hxx b/odb/mysql/transaction.hxx
index cd666b3..90182e1 100644
--- a/odb/mysql/transaction.hxx
+++ b/odb/mysql/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/mysql/transaction.ixx b/odb/mysql/transaction.ixx
index 5846632..39fb5d1 100644
--- a/odb/mysql/transaction.ixx
+++ b/odb/mysql/transaction.ixx
@@ -37,5 +37,11 @@ namespace odb
     {
       return implementation ().connection ();
     }
+
+    inline void transaction::
+    current (transaction& t)
+    {
+      odb::transaction::current (t);
+    }
   }
 }