Implement brep-migrate utility

1 files changed, 43 insertions, 0 deletions

diff --git a/brep/database-lock b/brep/database-lock
new file mode 100644
index 0000000..72036a1
--- /dev/null
+++ b/brep/database-lock
@@ -0,0 +1,43 @@
+// file      : brep/database-lock -*- C++ -*-
+// copyright : Copyright (c) 2014-2016 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef BREP_DATABASE_LOCK
+#define BREP_DATABASE_LOCK
+
+#include <memory>    // unique_ptr
+#include <exception>
+
+#include <odb/pgsql/forward.hxx>    // database, transaction
+#include <odb/pgsql/connection.hxx>
+
+namespace brep
+{
+  struct database_locked: std::exception
+  {
+    virtual char const*
+    what () const throw () {return "database locked";}
+  };
+
+  // Try to "lock" the PostgreSQL database in the constructor and release the
+  // lock in the destructor. Throw database_locked if the database is already
+  // locked by someone else. May also throw odb::pgsql::database_exception.
+  //
+  // This mechanism is used by the brep loader and schema migration tool to
+  // make sure they don't step on each others toes.
+  //
+  // Note: movable but not copyable.
+  //
+  class database_lock
+  {
+  public:
+    explicit
+    database_lock (odb::pgsql::database&);
+
+  private:
+    odb::pgsql::connection_ptr connection_;
+    std::unique_ptr<odb::pgsql::transaction> transaction_;
+  };
+}
+
+#endif // BREP_DATABASE_LOCK