Minor tweaks of BasicIo.mmap()

Author: jim-easterbrook

USAGE.rst

@@ -372,15 +372,7 @@ In some cases this includes writing to the data.
     buf = thumb.copy()
     thumb_im = PIL.Image.open(io.BytesIO(buf.data()))
 
-In python-exiv2 before v0.15.0 the memory block is converted to an object with a buffer interface.
-A Python memoryview_ can be used to access the data without copying.
-(Converting to bytes_ would make a copy of the data, which we don't usually want.)
-
-Warning: segmentation faults
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-Note that the memory block must not be deleted or resized while the memoryview exists.
-Doing so will invalidate the memoryview and may cause a segmentation fault:
+Since version 0.18.0 python-exiv2 releases the memoryview (when the memory block is resized or deleted) to prevent problems such as segmentation faults:
 
 .. code:: python
 
@@ -390,24 +382,10 @@ Doing so will invalidate the memoryview and may cause a segmentation fault:
     b'fred'
     >>> del buf
     >>> print(bytes(data))
-    b'en_G'
-
-Since version 0.18.0 python-exiv2 releases the memoryview (when the memory block is resized) to prevent problems:
-
-.. code:: python
-
-    >>> buf = exiv2.DataBuf(b'fred')
-    >>> data = buf.data()
-    >>> print(bytes(data))
-    b'fred'
-    >>> buf.alloc(128)
-    >>> print(bytes(data))
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     ValueError: operation forbidden on released memoryview object
 
-Unfortunately I haven't been able to make this work for memory block deletion.
-
 Buffer interface
 ----------------
 

src/interface/basicio.i

@@ -133,17 +133,8 @@ OUTPUT_BUFFER_RW(Exiv2::byte* buf, size_t rcount)
 %ignore Exiv2::BasicIo::mmap();
 
 // Convert mmap() result to a Python memoryview, assumes arg2 = isWriteable
-// The callback is used to call munmap when the memoryview is deleted
-RETURN_VIEW_CB(Exiv2::byte* mmap, $1 ? arg1->size() : 0,
-               arg2 ? PyBUF_WRITE : PyBUF_READ,
-               PyObject_GetAttrString(self, "_release"),)
-
-// Define callback function
-%extend Exiv2::BasicIo {
-    void _release(PyObject* ref) {
-        self->munmap();
-    };
-}
+RETURN_VIEW(Exiv2::byte* mmap, $1 ? arg1->size() : 0,
+            arg2 ? PyBUF_WRITE : PyBUF_READ,)
 
 // Release memoryviews when mmap or data is called
 %typemap(check, fragment="memoryview_funcs") bool isWriteable {
@@ -152,21 +143,25 @@ RETURN_VIEW_CB(Exiv2::byte* mmap, $1 ? arg1->size() : 0,
 
 // Release memoryviews when some other functions are called
 %typemap(ret, fragment="memoryview_funcs")
-        (int close), (int munmap), (long write), (size_t write) %{
+        (int close), (int munmap), (long write), (size_t write),
+        (void _release) %{
     release_views(self);
 %}
 
 // Add data() method for easy access
+// The callback is used to call munmap when the memoryview is deleted
 RETURN_VIEW_CB(Exiv2::byte* data, $1 ? arg1->size() : 0,
                arg2 ? PyBUF_WRITE : PyBUF_READ,
                PyObject_GetAttrString(self, "_release"),)
 %extend Exiv2::BasicIo {
     Exiv2::byte* data(bool isWriteable) {
-        if (!self->isopen())
-            self->open();
-        self->munmap();
+        self->open();
         return self->mmap(isWriteable);
     };
+    void _release(PyObject* ref) {
+        self->munmap();
+        self->close();
+    };
 }
 
 // Enable len(Exiv2::BasicIo)

src/swig-0_27_7/basicio_wrap.cxx

@@ -4874,15 +4874,14 @@ SWIGINTERN char const *Exiv2_BasicIo_ioType(Exiv2::BasicIo *self){
         }
         return "unknown";
     }
-SWIGINTERN void Exiv2_BasicIo__release(Exiv2::BasicIo *self,PyObject *ref){
-        self->munmap();
-    }
 SWIGINTERN Exiv2::byte *Exiv2_BasicIo_data(Exiv2::BasicIo *self,bool isWriteable){
-        if (!self->isopen())
-            self->open();
-        self->munmap();
+        self->open();
         return self->mmap(isWriteable);
     }
+SWIGINTERN void Exiv2_BasicIo__release(Exiv2::BasicIo *self,PyObject *ref){
+        self->munmap();
+        self->close();
+    }
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -5510,7 +5509,7 @@ SWIGINTERN PyObject *_wrap_BasicIo_mmap(PyObject *self, PyObject *args) {
   if (!resultobj)
   SWIG_fail;
   // Store a weak ref to the new memoryview
-  if (store_view(self, resultobj, PyObject_GetAttrString(self, "_release")))
+  if (store_view(self, resultobj, NULL))
   SWIG_fail;
 
   return resultobj;
@@ -5727,26 +5726,41 @@ SWIGINTERN PyObject *_wrap_BasicIo_ioType(PyObject *self, PyObject *args) {
 }
 
 
-SWIGINTERN PyObject *_wrap_BasicIo__release(PyObject *self, PyObject *args) {
+SWIGINTERN PyObject *_wrap_BasicIo_data(PyObject *self, PyObject *args) {
   PyObject *resultobj = 0;
   Exiv2::BasicIo *arg1 = (Exiv2::BasicIo *) 0 ;
-  PyObject *arg2 = (PyObject *) 0 ;
+  bool arg2 ;
   void *argp1 = 0 ;
   int res1 = 0 ;
+  bool val2 ;
+  int ecode2 = 0 ;
   PyObject * obj1 = 0 ;
+  Exiv2::byte *result = 0 ;
 
-  if (!PyArg_UnpackTuple(args, "BasicIo__release", 1, 1, &obj1)) SWIG_fail;
+  {
+    arg2 = false;
+  }
+  if (!PyArg_UnpackTuple(args, "BasicIo_data", 0, 1, &obj1)) SWIG_fail;
   res1 = SWIG_ConvertPtr(self, &argp1,SWIGTYPE_p_Exiv2__BasicIo, 0 |  0 );
   if (!SWIG_IsOK(res1)) {
-    SWIG_exception_fail(SWIG_ArgError(res1), "in method '" "BasicIo__release" "', argument " "1"" of type '" "Exiv2::BasicIo *""'"); 
+    SWIG_exception_fail(SWIG_ArgError(res1), "in method '" "BasicIo_data" "', argument " "1"" of type '" "Exiv2::BasicIo *""'"); 
   }
   arg1 = reinterpret_cast< Exiv2::BasicIo * >(argp1);
-  arg2 = obj1;
+  if (obj1) {
+    ecode2 = SWIG_AsVal_bool(obj1, &val2);
+    if (!SWIG_IsOK(ecode2)) {
+      SWIG_exception_fail(SWIG_ArgError(ecode2), "in method '" "BasicIo_data" "', argument " "2"" of type '" "bool""'");
+    } 
+    arg2 = static_cast< bool >(val2);
+  }
+  {
+    release_views(self);
+  }
   {
     try {
       {
         SWIG_PYTHON_THREAD_BEGIN_ALLOW;
-        Exiv2_BasicIo__release(arg1,arg2);
+        result = (Exiv2::byte *)Exiv2_BasicIo_data(arg1,arg2);
         SWIG_PYTHON_THREAD_END_ALLOW;
       }
     }
@@ -5755,48 +5769,40 @@ SWIGINTERN PyObject *_wrap_BasicIo__release(PyObject *self, PyObject *args) {
       SWIG_fail;
     }
   }
-  resultobj = SWIG_Py_Void();
+  
+  resultobj = PyMemoryView_FromMemory((char*)result, result ? arg1->size() : 0, arg2 ? PyBUF_WRITE : PyBUF_READ);
+  if (!resultobj)
+  SWIG_fail;
+  // Store a weak ref to the new memoryview
+  if (store_view(self, resultobj, PyObject_GetAttrString(self, "_release")))
+  SWIG_fail;
+  
   return resultobj;
 fail:
   return NULL;
 }
 
 
-SWIGINTERN PyObject *_wrap_BasicIo_data(PyObject *self, PyObject *args) {
+SWIGINTERN PyObject *_wrap_BasicIo__release(PyObject *self, PyObject *args) {
   PyObject *resultobj = 0;
   Exiv2::BasicIo *arg1 = (Exiv2::BasicIo *) 0 ;
-  bool arg2 ;
+  PyObject *arg2 = (PyObject *) 0 ;
   void *argp1 = 0 ;
   int res1 = 0 ;
-  bool val2 ;
-  int ecode2 = 0 ;
   PyObject * obj1 = 0 ;
-  Exiv2::byte *result = 0 ;
 
-  {
-    arg2 = false;
-  }
-  if (!PyArg_UnpackTuple(args, "BasicIo_data", 0, 1, &obj1)) SWIG_fail;
+  if (!PyArg_UnpackTuple(args, "BasicIo__release", 1, 1, &obj1)) SWIG_fail;
   res1 = SWIG_ConvertPtr(self, &argp1,SWIGTYPE_p_Exiv2__BasicIo, 0 |  0 );
   if (!SWIG_IsOK(res1)) {
-    SWIG_exception_fail(SWIG_ArgError(res1), "in method '" "BasicIo_data" "', argument " "1"" of type '" "Exiv2::BasicIo *""'"); 
+    SWIG_exception_fail(SWIG_ArgError(res1), "in method '" "BasicIo__release" "', argument " "1"" of type '" "Exiv2::BasicIo *""'"); 
   }
   arg1 = reinterpret_cast< Exiv2::BasicIo * >(argp1);
-  if (obj1) {
-    ecode2 = SWIG_AsVal_bool(obj1, &val2);
-    if (!SWIG_IsOK(ecode2)) {
-      SWIG_exception_fail(SWIG_ArgError(ecode2), "in method '" "BasicIo_data" "', argument " "2"" of type '" "bool""'");
-    } 
-    arg2 = static_cast< bool >(val2);
-  }
-  {
-    release_views(self);
-  }
+  arg2 = obj1;
   {
     try {
       {
         SWIG_PYTHON_THREAD_BEGIN_ALLOW;
-        result = (Exiv2::byte *)Exiv2_BasicIo_data(arg1,arg2);
+        Exiv2_BasicIo__release(arg1,arg2);
         SWIG_PYTHON_THREAD_END_ALLOW;
       }
     }
@@ -5805,13 +5811,9 @@ SWIGINTERN PyObject *_wrap_BasicIo_data(PyObject *self, PyObject *args) {
       SWIG_fail;
     }
   }
+  resultobj = SWIG_Py_Void();
 
-  resultobj = PyMemoryView_FromMemory((char*)result, result ? arg1->size() : 0, arg2 ? PyBUF_WRITE : PyBUF_READ);
-  if (!resultobj)
-  SWIG_fail;
-  // Store a weak ref to the new memoryview
-  if (store_view(self, resultobj, PyObject_GetAttrString(self, "_release")))
-  SWIG_fail;
+  release_views(self);
 
   return resultobj;
 fail:
@@ -6033,8 +6035,8 @@ SWIGINTERN PyMethodDef SwigPyBuiltin__Exiv2__BasicIo_methods[] = {
 		":rtype: str\n"
 		":return: A class name such as \"FileIo\".\n"
 		"" },
-  { "_release", _wrap_BasicIo__release, METH_VARARGS, "" },
   { "data", _wrap_BasicIo_data, METH_VARARGS, "" },
+  { "_release", _wrap_BasicIo__release, METH_VARARGS, "" },
   { NULL, NULL, 0, NULL } /* Sentinel */
 };