experimenting with the buffer protocol

pyopencl/cffi_cl.py

-#from pyopencl._cl import PooledBuffer, MemoryPool
+from pyopencl._cl import PooledBuffer, MemoryPool
 from _cffi import _ffi, _lib
 import warnings
+import np
+import ctypes
 
 bitlog2 = _lib.bitlog2
 
@@ -53,7 +55,7 @@ for type_, d in _constants.iteritems():
 # {{{ exceptions
 
 class Error(Exception):
-    def __init__(self, routine, code, msg=""):
+    def __init__(self, msg='', routine='', code=0):
         self.routine = routine
         self.code = code
         self.what = msg
@@ -84,7 +86,7 @@ def _handle_error(error):
         klass = RuntimeError
     else:
         klass = Error
-    e = klass(_ffi.string(error.routine), error.code, _ffi.string(error.msg))
+    e = klass(routine=_ffi.string(error.routine), code=error.code, msg=_ffi.string(error.msg))
     _lib._free(error.routine)
     _lib._free(error.msg)
     _lib._free(error)
@@ -203,11 +205,30 @@ class MemoryObject(MemoryObjectHolder):
     pass
 
 
-def _c_buffer_from_obj(obj):
+def _c_buffer_from_obj(obj, writable=False):
     if obj is None:
         return _ffi.NULL, 0
-    # assume numpy array for now
-    return _ffi.cast('void *', obj.__array_interface__['data'][0]), obj.nbytes
+
+    # numpy array
+    if hasattr(obj, '__array_interface__'): # if writeable == False, some tests fail...
+        return _ffi.cast('void *', obj.__array_interface__['data'][0]), obj.nbytes
+
+    # ... ?
+    
+    # fall back to old CPython buffer protocol API
+    addr = ctypes.c_void_p()
+    length = ctypes.c_ssize_t()
+    try:
+        if writable:
+            status = ctypes.pythonapi.PyObject_AsWriteBuffer(ctypes.py_object(obj), ctypes.byref(addr), ctypes.byref(length))
+        else:
+            status = ctypes.pythonapi.PyObject_AsReadBuffer(ctypes.py_object(obj), ctypes.byref(addr), ctypes.byref(length))
+    except TypeError:
+        raise LogicError("", status_code.INVALID_VALUE, "PyOpencl does not accept bare Python types as arguments")
+    else:
+        if status:
+            raise Exception('TODO error_already_set')
+    return _ffi.cast('void *', addr.value), length.value
     
 class Buffer(MemoryObject):
     _id = 'buffer'
@@ -216,7 +237,7 @@ class Buffer(MemoryObject):
             warnings.warn("'hostbuf' was passed, but no memory flags to make use of it.")
         c_hostbuf = _ffi.NULL
         if hostbuf is not None:
-            c_hostbuf, hostbuf_size = _c_buffer_from_obj(hostbuf)
+            c_hostbuf, hostbuf_size = _c_buffer_from_obj(hostbuf, writable=flags & mem_flags.USE_HOST_PTR)
             if size > hostbuf_size:
                 raise RuntimeError("Buffer", status_code.INVALID_VALUE, "specified size is greater than host buffer size")
             if size == 0:
@@ -446,7 +467,7 @@ def _c_obj_list(objs=None):
     return _ffi.new('void *[]', [ev.ptr for ev in objs]), len(objs)
 
 def _enqueue_read_buffer(queue, mem, hostbuf, device_offset=0, wait_for=None, is_blocking=True):
-    c_buf, size = _c_buffer_from_obj(hostbuf)
+    c_buf, size = _c_buffer_from_obj(hostbuf, writable=True)
     ptr_event = _ffi.new('void **')
     c_wait_for, num_wait_for = _c_obj_list(wait_for)
     _handle_error(_lib._enqueue_read_buffer(
@@ -493,7 +514,7 @@ def _enqueue_write_buffer(queue, mem, hostbuf, device_offset=0, wait_for=None, i
     return _create_instance(Event, ptr_event[0])
 
 def _enqueue_read_image(queue, mem, origin, region, hostbuf, row_pitch=0, slice_pitch=0, wait_for=None, is_blocking=True):
-    c_buf, size = _c_buffer_from_obj(hostbuf)
+    c_buf, size = _c_buffer_from_obj(hostbuf, writable=True)
     ptr_event = _ffi.new('void **')
     c_wait_for, num_wait_for = _c_obj_list(wait_for)
     _handle_error(_lib._enqueue_read_image(
@@ -654,7 +675,7 @@ class Image(MemoryObject):
         if shape is None:
             raise LogicError("Image", status_code.INVALID_VALUE, "'shape' must be given")
 
-        c_buf, size = _c_buffer_from_obj(buffer)
+        c_buf, size = _c_buffer_from_obj(buffer, writable=flags & mem_flags.USE_HOST_PTR)
                 
         dims = len(shape)
         if dims == 2: