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diff --git a/gnuradio-core/src/lib/general/gr_feval.i b/gnuradio-core/src/lib/general/gr_feval.i
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@@ -0,0 +1,233 @@
+/* -*- c++ -*- */
+/*
+ * Copyright 2006,2010 Free Software Foundation, Inc.
+ *
+ * This file is part of GNU Radio
+ *
+ * GNU Radio is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3, or (at your option)
+ * any later version.
+ *
+ * GNU Radio is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GNU Radio; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+
+/*
+ * N.B., this is a _very_ non-standard SWIG .i file
+ *
+ * It contains a bunch of magic that is required to ensure that when
+ * these classes are used as base classes for python code,
+ * everything works when calling back from C++ into Python.
+ *
+ * The gist of the problem is that our C++ code is usually not holding
+ * the Python Global Interpreter Lock (GIL).  Thus if we invoke a
+ * "director" method from C++, we'll end up in Python not holding the
+ * GIL.  Disaster (SIGSEGV) will result.  To avoid this we insert a
+ * "shim" that grabs and releases the GIL.
+ *
+ * If you don't understand SWIG "directors" or the Python GIL,
+ * don't bother trying to understand what's going on in here.
+ *
+ * [We could eliminate a bunch of this hair by requiring SWIG 1.3.29
+ * or later and some additional magic declarations, but many systems
+ * aren't shipping that version yet.  Thus we kludge...]
+ */
+
+
+// Directors are only supported in Python, Java and C#
+#ifdef SWIGPYTHON
+%import "pmt_swig.i"
+using namespace pmt;
+
+// Enable SWIG directors for these classes
+%feature("director") gr_py_feval_dd;
+%feature("director") gr_py_feval_cc;
+%feature("director") gr_py_feval_ll;
+%feature("director") gr_py_feval;
+%feature("director") gr_py_feval_p;
+
+%feature("nodirector") gr_py_feval_dd::calleval;
+%feature("nodirector") gr_py_feval_cc::calleval;
+%feature("nodirector") gr_py_feval_ll::calleval;
+%feature("nodirector") gr_py_feval::calleval;
+%feature("nodirector") gr_py_feval_p::calleval;
+
+
+%rename(feval_dd) gr_py_feval_dd;
+%rename(feval_cc) gr_py_feval_cc;
+%rename(feval_ll) gr_py_feval_ll;
+%rename(feval)    gr_py_feval;
+%rename(feval_p)  gr_py_feval_p;
+
+//%exception {
+//  try { $action }
+//  catch (Swig::DirectorException &e) { std::cerr << e.getMessage();  SWIG_fail; }
+//}
+
+%{
+
+// class that ensures we acquire and release the Python GIL
+
+class ensure_py_gil_state {
+  PyGILState_STATE	d_gstate;
+public:
+  ensure_py_gil_state()  { d_gstate = PyGILState_Ensure(); }
+  ~ensure_py_gil_state() { PyGILState_Release(d_gstate); }
+};
+
+%}
+
+/*
+ * These are the real C++ base classes, however we don't want these exposed.
+ */
+%ignore gr_feval_dd;
+class gr_feval_dd
+{
+protected:
+  virtual double eval(double x);
+
+public:
+  gr_feval_dd() {}
+  virtual ~gr_feval_dd();
+
+  virtual double calleval(double x);
+};
+
+%ignore gr_feval_cc;
+class gr_feval_cc
+{
+protected:
+  virtual gr_complex eval(gr_complex x);
+
+public:
+  gr_feval_cc() {}
+  virtual ~gr_feval_cc();
+
+  virtual gr_complex calleval(gr_complex x);
+};
+
+%ignore gr_feval_ll;
+class gr_feval_ll
+{
+protected:
+  virtual long eval(long x);
+
+public:
+  gr_feval_ll() {}
+  virtual ~gr_feval_ll();
+
+  virtual long calleval(long x);
+};
+
+%ignore gr_feval;
+class gr_feval
+{
+protected:
+  virtual void eval();
+
+public:
+  gr_feval() {}
+  virtual ~gr_feval();
+
+  virtual void calleval();
+};
+
+%ignore gr_feval_p;
+class gr_feval_p
+{
+protected:
+  virtual void eval(pmt_t x);
+
+public:
+  gr_feval_p() {}
+  virtual ~gr_feval_p();
+
+  virtual void calleval(pmt_t x);
+};
+
+/*
+ * These are the ones to derive from in Python.  They have the magic shim
+ * that ensures that we're holding the Python GIL when we enter Python land...
+ */
+
+%inline %{
+#include <gruel/pmt.h>
+
+class gr_py_feval_dd : public gr_feval_dd
+{
+ public:
+  double calleval(double x)
+  {
+    ensure_py_gil_state _lock;
+    return eval(x);
+  }
+};
+
+class gr_py_feval_cc : public gr_feval_cc
+{
+ public:
+  gr_complex calleval(gr_complex x)
+  {
+    ensure_py_gil_state _lock;
+    return eval(x);
+  }
+};
+
+class gr_py_feval_ll : public gr_feval_ll
+{
+ public:
+  long calleval(long x)
+  {
+    ensure_py_gil_state _lock;
+    return eval(x);
+  }
+};
+
+class gr_py_feval : public gr_feval
+{
+ public:
+  void calleval()
+  {
+    ensure_py_gil_state _lock;
+    eval();
+  }
+};
+
+class gr_py_feval_p : public gr_feval_p
+{
+ public:
+  void calleval(pmt::pmt_t x)
+  {
+    ensure_py_gil_state _lock;
+    eval(x);
+  }
+};
+
+%}
+
+
+
+// examples / test cases
+
+%rename(feval_dd_example) gr_feval_dd_example;
+double gr_feval_dd_example(gr_feval_dd *f, double x);
+
+%rename(feval_cc_example) gr_feval_cc_example;
+gr_complex gr_feval_cc_example(gr_feval_cc *f, gr_complex x);
+
+%rename(feval_ll_example) gr_feval_ll_example;
+long gr_feval_ll_example(gr_feval_ll *f, long x);
+
+%rename(feval_example) gr_feval_example;
+void gr_feval_example(gr_feval *f);
+
+#endif // SWIGPYTHON