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.

4 files changed, 71 insertions, 28 deletions

diff --git a/odb/database.hxx b/odb/database.hxx
index 2e6c79d..5ec98a7 100644
--- a/odb/database.hxx
+++ b/odb/database.hxx
@@ -177,8 +177,8 @@ namespace odb
     // Transactions.
     //
   public:
-    transaction_impl*
-    begin ();
+    virtual transaction_impl*
+    begin () = 0;
 
     // Connections.
     //
diff --git a/odb/database.ixx b/odb/database.ixx
index ccbbe41..dbdcaec 100644
--- a/odb/database.ixx
+++ b/odb/database.ixx
@@ -12,12 +12,6 @@ namespace odb
   {
   }
 
-  inline transaction_impl* database::
-  begin ()
-  {
-    return connection ()->begin ();
-  }
-
   inline connection_ptr database::
   connection ()
   {
diff --git a/odb/transaction.cxx b/odb/transaction.cxx
index e1fed91..70abd0c 100644
--- a/odb/transaction.cxx
+++ b/odb/transaction.cxx
@@ -19,10 +19,16 @@ namespace odb
   static ODB_TLS_POINTER (transaction) current_transaction;
 
   transaction::
-  transaction (transaction_impl* impl)
+  transaction (transaction_impl* impl, bool make_current)
       : finalized_ (false), impl_ (impl)
   {
-    tls_set (current_transaction, this);
+    if (make_current && tls_get (current_transaction) != 0)
+      throw already_in_transaction ();
+
+    impl_->start ();
+
+    if (make_current)
+      tls_set (current_transaction, this);
   }
 
   transaction::
@@ -60,14 +66,32 @@ namespace odb
   }
 
   void transaction::
+  current (transaction& t)
+  {
+    tls_set (current_transaction, &t);
+  }
+
+  void transaction::
+  reset_current ()
+  {
+    transaction* t (0);
+    tls_set (current_transaction, t);
+  }
+
+  void transaction::
   commit ()
   {
     if (finalized_)
       throw transaction_already_finalized ();
 
     finalized_ = true;
-    transaction* t (0);
-    tls_set (current_transaction, t);
+
+    if (tls_get (current_transaction) == this)
+    {
+      transaction* t (0);
+      tls_set (current_transaction, t);
+    }
+
     impl_->commit ();
   }
 
@@ -78,8 +102,13 @@ namespace odb
       throw transaction_already_finalized ();
 
     finalized_ = true;
-    transaction* t (0);
-    tls_set (current_transaction, t);
+
+    if (tls_get (current_transaction) == this)
+    {
+      transaction* t (0);
+      tls_set (current_transaction, t);
+    }
+
     impl_->rollback ();
   }
 
diff --git a/odb/transaction.hxx b/odb/transaction.hxx
index c2b1f77..0d4f518 100644
--- a/odb/transaction.hxx
+++ b/odb/transaction.hxx
@@ -22,8 +22,11 @@ namespace odb
     typedef odb::database database_type;
     typedef odb::connection connection_type;
 
+    // If the second argument is false, then this transaction is not
+    // made the current transaction of the thread.
+    //
     explicit
-    transaction (transaction_impl*);
+    transaction (transaction_impl*, bool make_current = true);
 
     // Unless the transaction has already been finalized (explicitly
     // committed or rolled back), the destructor will roll it back.
@@ -46,16 +49,26 @@ namespace odb
     connection_type&
     connection ();
 
+    // Return true if there is a transaction in effect.
+    //
+    static bool
+    has_current ();
+
     // Return current transaction or throw if there is no transaction
     // in effect.
     //
     static transaction&
     current ();
 
-    // Return true if there is a transaction in effect.
+    // Set the current thread's transaction.
     //
-    static bool
-    has_current ();
+    static void
+    current (transaction&);
+
+    // Revert to the no transaction in effect state for the current thread.
+    //
+    static void
+    reset_current ();
 
   public:
     transaction_impl&
@@ -74,21 +87,17 @@ namespace odb
 
   class LIBODB_EXPORT transaction_impl
   {
-  protected:
-    friend class transaction;
-
+  public:
     typedef odb::database database_type;
     typedef odb::connection connection_type;
 
-    transaction_impl (database_type& db, connection_type& c)
-      : database_ (db), connection_ (c)
-    {
-    }
-
     virtual
     ~transaction_impl ();
 
     virtual void
+    start () = 0;
+
+    virtual void
     commit () = 0;
 
     virtual void
@@ -103,12 +112,23 @@ namespace odb
     connection_type&
     connection ()
     {
-      return connection_;
+      return *connection_;
+    }
+
+  protected:
+    transaction_impl (database_type& db)
+        : database_ (db), connection_ (0)
+    {
+    }
+
+    transaction_impl (database_type& db, connection_type& c)
+        : database_ (db), connection_ (&c)
+    {
     }
 
   protected:
     database_type& database_;
-    connection_type& connection_;
+    connection_type* connection_;
   };
 }