Bugfix: do not release Python GIL before script did clean-up

plugins/gui/include/gui/python/python_thread.h

@@ -35,6 +35,26 @@ namespace hal {
     class Module;
     class Gate;
 
+    /**
+     * Class to aquire and release GIL
+     *
+     * It is important that the GIL is not released before
+     * Python code has removed all objects created during
+     * execution. Therefore the GIL release is done at the
+     * very end when running out of scope and calling the
+     * destructor
+     */
+    class PythonMutex
+    {
+        int mState;
+    public:
+        /// Aquire GIL
+        PythonMutex();
+
+        /// Release GIL
+        ~PythonMutex();
+    };
+
     class PythonThread : public QThread, public PythonContextSubscriber
     {
     public:

plugins/gui/src/python/python_thread.cpp

@@ -11,6 +11,16 @@
 #include <QDebug>
 
 namespace hal {
+    PythonMutex::PythonMutex()
+    {
+        mState = PyGILState_Ensure();
+    }
+
+    PythonMutex::~PythonMutex()
+    {
+        PyGILState_Release((PyGILState_STATE)mState);
+    }
+
     PythonThread::PythonThread(const QString& script, bool singleStatement, QObject* parent)
         : QThread(parent), mScript(script), mSingleStatement(singleStatement),
           mAbortRequested(false), mSpamCount(0)
@@ -26,7 +36,7 @@ namespace hal {
     void PythonThread::run()
     {
         // decides it's our turn.
-        PyGILState_STATE state = PyGILState_Ensure();
+        PythonMutex pmutex;
         py::dict tmp_context(py::globals());
         PythonContext::initializeScript(&tmp_context);
 
@@ -60,7 +70,7 @@ namespace hal {
             mErrorMessage = QString::fromStdString(std::string(e.what()) + "#\n");
         }
 
-        PyGILState_Release(state);
+       // running out of scope calls PyGILState_Release(state);
     }
 
     void PythonThread::handleStdout(const QString& output)
@@ -114,7 +124,7 @@ namespace hal {
             mInputMutex.unlock();
         }
         qDebug() << "about to terminate thread..." << mPythonThreadID;
-        PyGILState_STATE state = PyGILState_Ensure();
+        PythonMutex pmutex;
         // We interrupt the thread by forcibly injecting an exception
         // (namely the KeyboardInterrupt exception, but any other one works as well)
         int nThreads = PyThreadState_SetAsyncExc(mPythonThreadID, PyExc_KeyboardInterrupt);
@@ -127,8 +137,8 @@ namespace hal {
             // apparently this can actually happen if you mess up the C<->Python bindings
             qDebug() << "Oh no! There seem to be multiple threads with the same ID!";
         }
-        PyGILState_Release(state);
         qDebug() << "thread terminated";
+        // running out of scope calls PyGILState_Release(state);
     }
 
     bool PythonThread::getInput(InputType type, QString prompt, QVariant defaultValue)