Implement python backend

1 files changed, 419 insertions, 0 deletions

diff --git a/backends/python.c b/backends/python.c
new file mode 100644
index 0000000..9fad0ae
--- /dev/null
+++ b/backends/python.c
@@ -0,0 +1,419 @@
+#define BACKEND_NAME "python"
+
+#define PY_SSIZE_T_CLEAN
+#include <string.h>
+#include <Python.h>
+#include "python.h"
+
+#define MMPY_INSTANCE_KEY "midimonster_instance"
+
+/*
+ * TODO might want to export the full MM_API set to python at some point
+ */
+
+static PyThreadState* python_main = NULL;
+static wchar_t* program_name = NULL;
+
+MM_PLUGIN_API int init(){
+	backend python = {
+		.name = BACKEND_NAME,
+		.conf = python_configure,
+		.create = python_instance,
+		.conf_instance = python_configure_instance,
+		.channel = python_channel,
+		.handle = python_set,
+		.process = python_handle,
+		.start = python_start,
+		.shutdown = python_shutdown
+	};
+
+	//register backend
+	if(mm_backend_register(python)){
+		LOG("Failed to register backend");
+		return 1;
+	}
+	return 0;
+}
+
+static int python_configure(char* option, char* value){
+	LOG("No backend configuration possible");
+	return 1;
+}
+
+static int python_prepend_str(PyObject* list, char* str){
+	if(!list || !str){
+		return 1;
+	}
+
+	PyObject* item = PyUnicode_FromString(str);
+	if(!item){
+		return 1;
+	}
+
+	if(PyList_Insert(list, 0, item) < 0){
+		Py_DECREF(item);
+		return 1;
+	}
+	Py_DECREF(item);
+	return 0;
+}
+
+static PyObject* mmpy_output(PyObject* self, PyObject* args){
+	instance* inst = *((instance**) PyModule_GetState(self));
+	python_instance_data* data = (python_instance_data*) inst->impl;
+	const char* channel_name = NULL;
+	channel* chan = NULL;
+	channel_value val = {
+		0
+	};
+	size_t u;
+
+	if(!PyArg_ParseTuple(args, "sd", &channel_name, &val.normalised)){
+		return NULL;
+	}
+
+	val.normalised = clamp(val.normalised, 1.0, 0.0);
+
+	for(u = 0; u < data->channels; u++){
+		if(!strcmp(data->channel[u].name, channel_name)){
+			DBGPF("Setting channel %s.%s to %f", inst->name, channel_name, val.normalised);
+			chan = mm_channel(inst, u, 0);
+			//this should never happen
+			if(!chan){
+				LOGPF("Failed to fetch parsed channel %s.%s", inst->name, channel_name);
+				break;
+			}
+			data->channel[u].out = val.normalised;
+			mm_channel_event(chan, val);
+			break;
+		}
+	}
+
+	if(u == data->channels){
+		DBGPF("Output on unknown channel %s.%s, no event pushed", inst->name, channel_name);
+	}
+
+	Py_INCREF(Py_None);
+	return Py_None;
+}
+
+static PyObject* mmpy_channel_value(PyObject* self, PyObject* args, uint8_t in){
+	instance* inst = *((instance**) PyModule_GetState(self));
+	python_instance_data* data = (python_instance_data*) inst->impl;
+	const char* channel_name = NULL;
+	size_t u;
+
+	if(!PyArg_ParseTuple(args, "s", &channel_name)){
+		return NULL;
+	}
+
+	for(u = 0; u < data->channels; u++){
+		if(!strcmp(data->channel[u].name, channel_name)){
+			return PyFloat_FromDouble(in ? data->channel[u].in : data->channel[u].out);
+		}
+	}
+
+	Py_INCREF(Py_None);
+	return Py_None;
+}
+
+static PyObject* mmpy_current_handler(PyObject* self, PyObject* args){
+	instance* inst = *((instance**) PyModule_GetState(self));
+	python_instance_data* data = (python_instance_data*) inst->impl;
+
+	if(data->current_channel){
+		return PyUnicode_FromString(data->current_channel->name);
+	}
+
+	Py_INCREF(Py_None);
+	return Py_None;
+}
+
+static PyObject* mmpy_output_value(PyObject* self, PyObject* args){
+	return mmpy_channel_value(self, args, 0);
+}
+
+static PyObject* mmpy_input_value(PyObject* self, PyObject* args){
+	return mmpy_channel_value(self, args, 1);
+}
+
+static int mmpy_exec(PyObject* module) {
+	instance** inst = (instance**) PyModule_GetState(module);
+	//FIXME actually use interpreter dict (from python 3.8) here at some point
+	PyObject* capsule = PyDict_GetItemString(PyThreadState_GetDict(), MMPY_INSTANCE_KEY);
+	if(capsule && inst){
+		*inst = PyCapsule_GetPointer(capsule, NULL);
+		return 0;
+	}
+
+	//TODO raise exception
+	return -1;
+}
+
+static int python_configure_instance(instance* inst, char* option, char* value){
+	python_instance_data* data = (python_instance_data*) inst->impl;
+	PyObject* module = NULL;
+
+	//load python script
+	if(!strcmp(option, "module")){
+		//swap to interpreter
+		PyEval_RestoreThread(data->interpreter);
+		//import the module
+		module = PyImport_ImportModule(value);
+		if(!module){
+			LOGPF("Failed to import module %s to instance %s", value, inst->name);
+			PyErr_Print();
+		}
+		Py_XDECREF(module);
+		PyEval_ReleaseThread(data->interpreter);
+		return 0;
+	}
+
+	LOGPF("Unknown instance parameter %s for instance %s", option, inst->name);
+	return 1;
+}
+
+static PyObject* mmpy_init(){
+	static PyModuleDef_Slot mmpy_slots[] = {
+		{Py_mod_exec, (void*) mmpy_exec},
+		{0}
+	};
+
+	static PyMethodDef mmpy_methods[] = {
+		{"output", mmpy_output, METH_VARARGS, "Output a channel event"},
+		{"inputvalue", mmpy_input_value, METH_VARARGS, "Get last input value for a channel"},
+		{"outputvalue", mmpy_output_value, METH_VARARGS, "Get the last output value for a channel"},
+		{"current", mmpy_current_handler, METH_VARARGS, "Get the name of the currently executing channel handler"},
+		{0}
+	};
+
+	static struct PyModuleDef mmpy = {
+		PyModuleDef_HEAD_INIT,
+		"midimonster",
+		NULL, /*doc size*/
+		sizeof(instance*),
+		mmpy_methods,
+		mmpy_slots
+	};
+
+	//single-phase init
+	//return PyModule_Create(&mmpy);
+
+	//multi-phase init
+	return PyModuleDef_Init(&mmpy);
+}
+
+static int python_instance(instance* inst){
+	python_instance_data* data = calloc(1, sizeof(python_instance_data));
+	PyObject* interpreter_dict = NULL;
+	char current_directory[8192];
+	if(!data){
+		LOG("Failed to allocate memory");
+		return 1;
+	}
+
+	//lazy-init because we need the interpreter running before _start,
+	//but don't want it running if no instances are defined
+	if(!python_main){
+		LOG("Initializing main python interpreter");
+		if(PyImport_AppendInittab("midimonster", &mmpy_init)){
+			LOG("Failed to extend python inittab for main interpreter");
+		}
+		program_name = Py_DecodeLocale("midimonster", NULL);
+		Py_SetProgramName(program_name);
+		//initialize python
+		Py_InitializeEx(0);
+		//create, acquire and release the GIL
+		PyEval_InitThreads();
+		python_main = PyEval_SaveThread();
+	}
+
+	//acquire the GIL before creating a new interpreter
+	PyEval_RestoreThread(python_main);
+	//create subinterpreter for new instance
+	data->interpreter = Py_NewInterpreter();
+
+	//push cwd as import path
+	if(getcwd(current_directory, sizeof(current_directory))){
+		if(python_prepend_str(PySys_GetObject("path"), current_directory)){
+			LOG("Failed to push current working directory to python");
+			goto bail;
+		}
+	}
+
+	//push the instance pointer for later module initialization
+	//FIXME python 3.8 introduces interpreter_dict = PyInterpreterState_GetDict(data->interpreter->interp);
+	//for now use thread state...
+	interpreter_dict = PyThreadState_GetDict();
+	if(!interpreter_dict){
+		LOG("Failed to access per-interpreter data storage");
+		goto bail;
+	}
+	//FIXME this might leak a reference to the capsule
+	if(PyDict_SetItemString(interpreter_dict, MMPY_INSTANCE_KEY, PyCapsule_New(inst, NULL, NULL))){
+		LOG("Failed to set per-interpreter instance pointer");
+		goto bail;
+	}
+
+	//NewInterpreter leaves us with the GIL, drop it
+	PyEval_ReleaseThread(data->interpreter);
+	inst->impl = data;
+	return 0;
+
+bail:
+	if(data->interpreter){
+		PyEval_ReleaseThread(data->interpreter);
+	}
+	free(data);
+	return 1;
+}
+
+static channel* python_channel(instance* inst, char* spec, uint8_t flags){
+	python_instance_data* data = (python_instance_data*) inst->impl;
+	size_t u;
+
+	for(u = 0; u < data->channels; u++){
+		if(!strcmp(data->channel[u].name, spec)){
+			break;
+		}
+	}
+
+	if(u == data->channels){
+		data->channel = realloc(data->channel, (data->channels + 1) * sizeof(mmpython_channel));
+		if(!data->channel){
+			data->channels = 0;
+			LOG("Failed to allocate memory");
+			return NULL;
+		}
+		memset(data->channel + u, 0, sizeof(mmpython_channel));
+
+		data->channel[u].name = strdup(spec);
+		if(!data->channel[u].name){
+			LOG("Failed to allocate memory");
+			return NULL;
+		}
+		data->channels++;
+	}
+
+	return mm_channel(inst, u, 1);
+}
+
+static int python_set(instance* inst, size_t num, channel** c, channel_value* v){
+	python_instance_data* data = (python_instance_data*) inst->impl;
+	mmpython_channel* chan = NULL;
+	PyObject* result = NULL;
+	size_t u;
+
+	//swap to interpreter
+	PyEval_RestoreThread(data->interpreter);
+
+	for(u = 0; u < num; u++){
+		chan = data->channel + c[u]->ident;
+
+		//update input value buffer
+		chan->in = v[u].normalised;
+
+		//call handler if present
+		if(chan->handler){
+			DBGPF("Calling handler for %s.%s", inst->name, chan->name);
+			data->current_channel = chan;
+			result = PyObject_CallFunction(chan->handler, "d", chan->in);
+			Py_XDECREF(result);
+			data->current_channel = NULL;
+			DBGPF("Done with handler for %s.%s", inst->name, chan->name);
+		}
+	}
+
+	PyEval_ReleaseThread(data->interpreter);
+	return 0;
+}
+
+static int python_handle(size_t num, managed_fd* fds){
+	//TODO implement some kind of intervaling functionality before people get it in their heads to start `import threading`
+	return 0;
+}
+
+static int python_start(size_t n, instance** inst){
+	python_instance_data* data = NULL;
+	PyObject* module = NULL;
+	size_t u, p;
+	char* module_name = NULL, *channel_name = NULL;
+
+	//resolve channel references to handler functions
+	for(u = 0; u < n; u++){
+		data = (python_instance_data*) inst[u]->impl;
+
+		//switch to interpreter
+		PyEval_RestoreThread(data->interpreter);
+		for(p = 0; p < data->channels; p++){
+			module = PyImport_AddModule("__main__");
+			channel_name = data->channel[p].name;
+			module_name = strchr(channel_name, '.');
+			if(module_name){
+				*module_name = 0;
+				//returns borrowed reference
+				module = PyImport_AddModule(channel_name);
+
+				if(!module){
+					LOGPF("Module %s for qualified channel %s.%s is not loaded on instance %s", channel_name, channel_name, module_name + 1, inst[u]->name);
+					return 1;
+				}
+
+				*module_name = '.';
+				channel_name = module_name + 1;
+			}
+
+			//returns new reference
+			data->channel[p].handler = PyObject_GetAttrString(module, channel_name);
+		}
+
+		//release interpreter
+		PyEval_ReleaseThread(data->interpreter);
+	}
+	return 0;
+}
+
+static int python_shutdown(size_t n, instance** inst){
+	size_t u, p;
+	python_instance_data* data = NULL;
+
+	//clean up channels
+	//this needs to be done before stopping the interpreters,
+	//because the handler references are refcounted
+	for(u = 0; u < n; u++){
+		data = (python_instance_data*) inst[u]->impl;
+		for(p = 0; p < data->channels; p++){
+			free(data->channel[p].name);
+			Py_XDECREF(data->channel[p].handler);
+		}
+		free(data->channel);
+		//do not free data here, needed for shutting down interpreters
+	}
+
+	if(python_main){
+		//just used to lock the GIL
+		PyEval_RestoreThread(python_main);
+
+		for(u = 0; u < n; u++){
+			data = (python_instance_data*) inst[u]->impl;
+			DBGPF("Shutting down interpreter for instance %s", inst[u]->name);
+			//swap to interpreter and end it, GIL is held after this but state is NULL
+			PyThreadState_Swap(data->interpreter);
+			PyErr_Clear();
+			//PyThreadState_Clear(data->interpreter);
+			Py_EndInterpreter(data->interpreter);
+
+			free(data);
+		}
+
+		//shut down main interpreter
+		PyThreadState_Swap(python_main);
+		if(Py_FinalizeEx()){
+			LOG("Failed to destroy python interpreters");
+		}
+		PyMem_RawFree(program_name);
+	}
+
+	LOG("Backend shut down");
+	return 0;
+}