Split py_context into py_thread_context and py_ensure_gil.

Slightly different handling of the GIL is required for newly-created C
threads vs functions that are either running in the main thread or from
a correctly-initialised C thread.

src/helpers.hpp

@@ -6,11 +6,12 @@
 #include "helpers.h"
 #include <Python.h>
 
-class py_context {
+/* entry points to threads should grab a py_thread_context for the duration of the thread */
+class py_thread_context {
 public:
-  py_context() { gstate = PyGILState_Ensure(); }
+  py_thread_context() { gstate = PyGILState_Ensure(); }
 
-  ~py_context() {
+  ~py_thread_context() {
     PyGILState_Release(gstate);
     if (PyGILState_Check() == 1)
       pts = PyEval_SaveThread();
@@ -21,6 +22,21 @@ class py_context {
   PyThreadState *pts;
 };
 
+/* anywhere needing to call python functions (that isn't using py_thread_context) should create a py_ensure_gil object */
+class py_ensure_gil {
+public:
+  py_ensure_gil() {
+    gstate = PyGILState_Ensure();
+  }
+
+  ~py_ensure_gil() {
+    PyGILState_Release(gstate);
+  }
+
+private:
+  PyGILState_STATE gstate;
+};
+
 // v8 to Python
 PyObject *BuildPyArray(Napi::Env env, Napi::Value arg);
 PyObject *BuildPyDict(Napi::Env env, Napi::Value arg);

src/pynode.cpp

@@ -43,6 +43,9 @@ Napi::Value StartInterpreter(const Napi::CallbackInfo &info) {
         .ThrowAsJavaScriptException();
   }
 
+  /* Release the GIL. The other entry points back into Python re-acquire it */
+  PyEval_SaveThread();
+
   return env.Null();
 }
 
@@ -86,7 +89,7 @@ Napi::Value AppendSysPath(const Napi::CallbackInfo &info) {
            pathName.c_str());
 
   {
-    py_context ctx;
+    py_ensure_gil ctx;
     PyRun_SimpleString(appendPathStr);
     free(appendPathStr);
   }
@@ -106,7 +109,7 @@ Napi::Value OpenFile(const Napi::CallbackInfo &info) {
   std::string fileName = info[0].As<Napi::String>().ToString();
 
   {
-    py_context ctx;
+    py_ensure_gil ctx;
 
     PyObject *pName;
     pName = PyUnicode_DecodeFSDefault(fileName.c_str());
@@ -136,7 +139,7 @@ Napi::Value ImportModule(const Napi::CallbackInfo &info) {
   std::string moduleName = info[0].As<Napi::String>().ToString();
 
   {
-    py_context ctx;
+    py_ensure_gil ctx;
 
     PyObject *pName;
     pName = PyUnicode_FromString(moduleName.c_str());
@@ -167,7 +170,7 @@ Napi::Value Eval(const Napi::CallbackInfo &info) {
   std::string statement = info[0].As<Napi::String>().ToString();
   int response;
   {
-    py_context ctx;
+    py_ensure_gil ctx;
 
     response = PyRun_SimpleString(statement.c_str());
   }
@@ -197,7 +200,8 @@ Napi::Value Call(const Napi::CallbackInfo &info) {
   PyObject *pFunc, *pArgs;
 
   {
-    py_context ctx;
+      printf("getting gil\n");
+    py_ensure_gil ctx;
 
     pFunc = PyObject_GetAttrString(pModule, functionName.c_str());
     int callable = PyCallable_Check(pFunc);

src/pywrapper.cpp

@@ -34,7 +34,7 @@ PyNodeWrappedPythonObject::PyNodeWrappedPythonObject(const Napi::CallbackInfo &i
 Napi::FunctionReference PyNodeWrappedPythonObject::constructor;
 
 Napi::Value PyNodeWrappedPythonObject::GetAttr(const Napi::CallbackInfo &info){
-    py_context ctx;
+    py_ensure_gil ctx;
     Napi::Env env = info.Env();
     std::string attrname = info[0].As<Napi::String>().ToString();
     PyObject * attr = PyObject_GetAttrString(this->_value, attrname.c_str());
@@ -48,7 +48,7 @@ Napi::Value PyNodeWrappedPythonObject::GetAttr(const Napi::CallbackInfo &info){
 }
 
 Napi::Value PyNodeWrappedPythonObject::Call(const Napi::CallbackInfo &info){
-    py_context ctx;
+    py_ensure_gil ctx;
     Napi::Env env = info.Env();
     int callable = PyCallable_Check(this->_value);
     if (! callable) {
@@ -73,7 +73,7 @@ Napi::Value PyNodeWrappedPythonObject::Call(const Napi::CallbackInfo &info){
 }
 
 Napi::Value PyNodeWrappedPythonObject::Repr(const Napi::CallbackInfo &info){
-    py_context ctx;
+    py_ensure_gil ctx;
     Napi::Env env = info.Env();
     std::string attrname = info[0].As<Napi::String>().ToString();
     PyObject * repr = PyObject_Repr(this->_value);

src/worker.cpp

@@ -10,7 +10,7 @@ PyNodeWorker::~PyNodeWorker(){};
 
 void PyNodeWorker::Execute() {
   {
-    py_context ctx;
+    py_thread_context ctx;
 
     pValue = PyObject_CallObject(pFunc, pyArgs);
     Py_DECREF(pyArgs);
@@ -47,7 +47,7 @@ void PyNodeWorker::Execute() {
 }
 
 void PyNodeWorker::OnOK() {
-  py_context ctx;
+  py_thread_context ctx;
   Napi::HandleScope scope(Env());
 
   std::vector<Napi::Value> result = {Env().Null(), Env().Null()};