Release the Python global interpreter lock during expensive operations

wrappers/python/src/swig_doxygen/swig_lib/python/exceptions.i

@@ -8,4 +8,24 @@
     }
 }
 
+%exception *::step {
+    try {
+        Py_BEGIN_ALLOW_THREADS
+        $action
+        Py_END_ALLOW_THREADS
+    } catch (std::exception &e) {
+        PyErr_SetString(PyExc_Exception, const_cast<char*>(e.what()));
+        return NULL;
+    }
+}
 
+%exception OpenMM::LocalEnergyMinimizer::minimize {
+    try {
+        Py_BEGIN_ALLOW_THREADS
+        $action
+        Py_END_ALLOW_THREADS
+    } catch (std::exception &e) {
+        PyErr_SetString(PyExc_Exception, const_cast<char*>(e.what()));
+        return NULL;
+    }
+}

wrappers/python/src/swig_doxygen/swig_lib/python/extend.i

@@ -6,13 +6,16 @@
                             int getParameters,
                             int enforcePeriodic,
                             int groups) {
+    State state;
+    Py_BEGIN_ALLOW_THREADS
     int types = 0;
     if (getPositions) types |= State::Positions;
     if (getVelocities) types |= State::Velocities;
     if (getForces) types |= State::Forces;
     if (getEnergy) types |= State::Energy;
     if (getParameters) types |= State::Parameters;
-    State state = self->getState(types, enforcePeriodic, groups);
+    state = self->getState(types, enforcePeriodic, groups);
+    Py_END_ALLOW_THREADS
     return _convertStateToLists(state);
   }
 
@@ -122,13 +125,16 @@ Parameters:
                             int getParameters,
                             int enforcePeriodic,
                             int groups) {
+    State state;
+    Py_BEGIN_ALLOW_THREADS
     int types = 0;
     if (getPositions) types |= State::Positions;
     if (getVelocities) types |= State::Velocities;
     if (getForces) types |= State::Forces;
     if (getEnergy) types |= State::Energy;
     if (getParameters) types |= State::Parameters;
-    State state = self->getState(copy, types, enforcePeriodic, groups);
+    state = self->getState(copy, types, enforcePeriodic, groups);
+    Py_END_ALLOW_THREADS
     return _convertStateToLists(state);
   }