ToPython: fix for multiple simultaneous instances

Author: Benjamin Chrétien

include/roboptim/core/python/to-python.hh

@@ -25,6 +25,7 @@ namespace roboptim
   namespace python
   {
     /// \brief Helper to run Python commands in the Python interpreter.
+    /// WARNING: this is not thread-safe for now (GIL etc.).
     class ToPython
     {
     public:
@@ -50,6 +51,9 @@ namespace roboptim
       void operator >> (std::ostream& o);
 
     private:
+      /// \brief Number of instances.
+      static int instances_;
+
       /// \brief Buffering callback.
       /// \param s string added to the buffer.
       void buffering (const std::string& s);

src/to-python.cc

@@ -189,22 +189,32 @@ namespace roboptim
     /********************************
      *  Implementation of ToPython  *
      ********************************/
+    int ToPython::instances_ = 0;
 
     ToPython::ToPython () : buffer_ ()
     {
-      PyImport_AppendInittab ("redir", PyInit_redir);
-      Py_Initialize ();
-      PyImport_ImportModule ("redir");
-
-      // Switch sys.stdout to custom handler
-      stdout_write_type write = boost::bind (&ToPython::buffering,
-                                             this, _1);
-      set_stdout (write);
+      if (!instances_)
+      {
+        PyImport_AppendInittab ("redir", PyInit_redir);
+        Py_Initialize ();
+        PyImport_ImportModule ("redir");
+
+        // Switch sys.stdout to custom handler
+        stdout_write_type write = boost::bind (&ToPython::buffering,
+                                               this, _1);
+        set_stdout (write);
+      }
+
+      // Increment the instance counter
+      instances_++;
     }
 
     ToPython::~ToPython ()
     {
-      Py_Exit (0);
+      // Decrement the instance counter
+      instances_--;
+
+      if (!instances_) Py_Finalize ();
     }
 
     const ToPython& ToPython::operator << (const char* cmd) const

tests/to-python-simultaneous.stdout

@@ -0,0 +1,3 @@
+foo
+bar
+42

tests/to-python.cc

@@ -24,13 +24,14 @@
 using namespace roboptim;
 using namespace roboptim::python;
 
-boost::shared_ptr<boost::test_tools::output_test_stream> output;
+typedef boost::shared_ptr<boost::test_tools::output_test_stream>
+output_ptr;
 
-BOOST_FIXTURE_TEST_SUITE (core, TestSuiteConfiguration)
+BOOST_AUTO_TEST_SUITE (to_python)
 
-BOOST_AUTO_TEST_CASE (to_python)
+BOOST_AUTO_TEST_CASE (redir)
 {
-  output = retrievePattern ("to-python");
+  output_ptr output = retrievePattern ("to-python");
 
   ToPython tp;
 
@@ -53,4 +54,27 @@ BOOST_AUTO_TEST_CASE (to_python)
   BOOST_CHECK (output->match_pattern ());
 }
 
+BOOST_AUTO_TEST_CASE (simultaneous)
+{
+  output_ptr output = retrievePattern ("to-python-simultaneous");
+
+  ToPython tp1;
+
+  tp1 << "print(\"foo\")";
+
+  {
+    ToPython tp2;
+    tp2 << "print(\"bar\")";
+    tp2 >> (*output);
+  }
+
+  tp1 << "print(42)";
+
+  // Flush to output
+  tp1 >> (*output);
+
+  std::cout << output->str () << std::endl;
+  BOOST_CHECK (output->match_pattern ());
+}
+
 BOOST_AUTO_TEST_SUITE_END ()