get rid of MutableBuffer

python/pyarrow/includes/libarrow.pxd

@@ -152,6 +152,7 @@ cdef extern from "arrow/api.h" namespace "arrow" nogil:
         uint8_t* data()
         int64_t size()
         shared_ptr[CBuffer] parent()
+        c_bool is_mutable() const
 
     cdef cppclass CMutableBuffer" arrow::MutableBuffer"(CBuffer):
         CMutableBuffer(const uint8_t* data, int64_t size)

python/pyarrow/io.pxi

@@ -532,7 +532,10 @@ cdef class Buffer:
         buffer.len = self.size
         buffer.ndim = 1
         buffer.obj = self
-        buffer.readonly = 1
+        if self.buffer.get().is_mutable():
+            buffer.readonly = 0
+        else:
+            buffer.readonly = 1
         buffer.shape = self.shape
         buffer.strides = self.strides
         buffer.suboffsets = NULL
@@ -549,35 +552,13 @@ cdef class Buffer:
             p[0] = <void*> self.buffer.get().data()
         return self.size
 
-
-cdef class MutableBuffer(Buffer):
-
-    def __cinit__(self):
-        pass
-
-    cdef void init_mutable(self, const shared_ptr[CMutableBuffer]& buffer):
-        Buffer.init(self, <shared_ptr[CBuffer]>(buffer))
-        self.mutable_buffer = buffer
-
-    def __getbuffer__(self, cp.Py_buffer* buffer, int flags):
-
-        buffer.buf = <char *>self.mutable_buffer.get().mutable_data()
-        buffer.format = 'b'
-        buffer.internal = NULL
-        buffer.itemsize = 1
-        buffer.len = self.size
-        buffer.ndim = 1
-        buffer.obj = self
-        buffer.readonly = 0
-        buffer.shape = self.shape
-        buffer.strides = self.strides
-        buffer.suboffsets = NULL
-
     def __getwritebuffer__(self, Py_ssize_t idx, void **p):
+        if not self.buffer.get().is_mutable():
+            raise SystemError("trying to write an immutable buffer")
         if idx != 0:
             raise SystemError("accessing non-existent buffer segment")
         if p != NULL:
-            p[0] = <void*> self.mutable_buffer.get().data()
+            p[0] = <void*> self.buffer.get().data()
         return self.size
 
 

python/pyarrow/lib.pxd

@@ -313,13 +313,6 @@ cdef class Buffer:
     cdef void init(self, const shared_ptr[CBuffer]& buffer)
 
 
-cdef class MutableBuffer(Buffer):
-    cdef:
-        shared_ptr[CMutableBuffer] mutable_buffer
-
-    cdef void init_mutable(self, const shared_ptr[CMutableBuffer]& buffer)
-
-
 cdef class NativeFile:
     cdef:
         shared_ptr[RandomAccessFile] rd_file

python/pyarrow/plasma.pyx

@@ -26,7 +26,7 @@ from libcpp.vector cimport vector as c_vector
 from libc.stdint cimport int64_t, uint8_t, uintptr_t
 from cpython.pycapsule cimport *
 
-from pyarrow.lib cimport Buffer, MutableBuffer, NativeFile, check_status
+from pyarrow.lib cimport Buffer, NativeFile, check_status
 from pyarrow.includes.libarrow cimport (CMutableBuffer, CBuffer,
                                         CFixedSizeBufferWriter, CStatus)
 
@@ -191,26 +191,6 @@ cdef class PlasmaBuffer(Buffer):
         self.client.release(self.object_id)
 
 
-cdef class MutablePlasmaBuffer(MutableBuffer):
-
-    cdef:
-        ObjectID object_id
-        PlasmaClient client
-
-    def __cinit__(self, ObjectID object_id, PlasmaClient client):
-        """Initialize a PlasmaBuffer."""
-        self.object_id = object_id
-        self.client = client
-
-    def __dealloc__(self):
-        """
-        Notify Plasma that the object is no longer needed.
-
-        If the plasma client has been shut down, then don't do anything.
-        """
-        self.client.release(self.object_id)
-
-
 cdef class PlasmaClient:
     """
     The PlasmaClient is used to interface with a plasma store and manager.
@@ -253,10 +233,10 @@ cdef class PlasmaClient:
 
     cdef _make_mutable_plasma_buffer(self, ObjectID object_id, uint8_t* data,
                                      int64_t size):
-        cdef shared_ptr[CMutableBuffer] buffer
+        cdef shared_ptr[CBuffer] buffer
         buffer.reset(new CMutableBuffer(data, size))
-        result = MutablePlasmaBuffer(object_id, self)
-        result.init_mutable(buffer)
+        result = PlasmaBuffer(object_id, self)
+        result.init(buffer)
         return result
 
     @property