Move batch API exposure to Python layer

Exposes the C core batch API to the Python layers. Provides a shim to
enable the old Python API to remain the same (for now).

src/python/src/grpc/_adapter/_server.h → src/python/src/grpc/_adapter/_c/module.c

@@ -31,21 +31,31 @@
  *
  */
 
-#ifndef _ADAPTER__SERVER_H_
-#define _ADAPTER__SERVER_H_
+#include <stdlib.h>
 
+#define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #include <grpc/grpc.h>
 
-#include "grpc/_adapter/_completion_queue.h"
+#include "grpc/_adapter/_c/types.h"
 
-typedef struct {
-  PyObject_HEAD
+static PyMethodDef c_methods[] = {
+    {NULL}
+};
 
-  CompletionQueue *completion_queue;
-  grpc_server *c_server;
-} Server;
+PyMODINIT_FUNC init_c(void) {
+  PyObject *module;
 
-int pygrpc_add_server(PyObject *module);
+  module = Py_InitModule3("_c", c_methods,
+                          "Wrappings of C structures and functions.");
 
-#endif /* _ADAPTER__SERVER_H_ */
+  if (pygrpc_module_add_types(module) < 0) {
+    return;
+  }
+
+  /* GRPC maintains an internal counter of how many times it has been
+     initialized and handles multiple pairs of grpc_init()/grpc_shutdown()
+     invocations accordingly. */
+  grpc_init();
+  atexit(&grpc_shutdown);
+}

src/python/src/grpc/_adapter/_completion_queue.h → src/python/src/grpc/_adapter/_c/types.c

@@ -31,19 +31,30 @@
  *
  */
 
-#ifndef _ADAPTER__COMPLETION_QUEUE_H_
-#define _ADAPTER__COMPLETION_QUEUE_H_
+#include "grpc/_adapter/_c/types.h"
 
+#define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #include <grpc/grpc.h>
 
-typedef struct {
-  PyObject_HEAD
-  grpc_completion_queue *c_completion_queue;
-} CompletionQueue;
-
-extern PyTypeObject pygrpc_CompletionQueueType;
-
-int pygrpc_add_completion_queue(PyObject *module);
-
-#endif /* _ADAPTER__COMPLETION_QUEUE_H_ */
+int pygrpc_module_add_types(PyObject *module) {
+  int i;
+  PyTypeObject *types[] = {
+      &pygrpc_ClientCredentials_type,
+      &pygrpc_ServerCredentials_type,
+      &pygrpc_CompletionQueue_type,
+      &pygrpc_Call_type,
+      &pygrpc_Channel_type,
+      &pygrpc_Server_type
+  };
+  for (i = 0; i < sizeof(types)/sizeof(PyTypeObject *); ++i) {
+    if (PyType_Ready(types[i]) < 0) {
+      return -1;
+    }
+  }
+  for (i = 0; i < sizeof(types)/sizeof(PyTypeObject *); ++i) {
+    Py_INCREF(types[i]);
+    PyModule_AddObject(module, types[i]->tp_name, (PyObject *)types[i]);
+  }
+  return 0;
+}