Commit 8fdc6b08 authored by Mat's avatar Mat
Browse files

Allow read-only shared array attachments (Closes: #15) 

It can be convenient to be able to attach a shared array in read-only
mode, in order to enforce a single writer multiple reader scenario.
parent ce735c33

README.md

+4 −2
Original line number Diff line number Diff line
@@ -66,13 +66,15 @@ won't be lost when the numpy array is deleted, nor when the python 
interpreter exits. To delete a shared array and reclaim system

resources use the `SharedArray.delete()` function.

 

### SharedArray.attach(name)

### SharedArray.attach(name, ro=False)



This function attaches a previously created array in shared memory

identified by `name`, which can use the `file://` prefix to indicate

that the array is stored as a file, or `shm://` to indicate that the

array is stored as a POSIX shared memory object. For backward

compatibility `shm://` is assumed when no prefix is given.

compatibility `shm://` is assumed when no prefix is given. The

optional parameter `ro` indicates that the array shall be attached

read-only.



An array may be simultaneously attached from multiple different

processes (i.e. python interpreters).

src/shared_array.c

+1 −1
Original line number Diff line number Diff line
@@ -43,7 +43,7 @@ static PyMethodDef module_functions[] = { 
	  "Create a numpy array in shared memory" },



	{ "attach", (PyCFunction) shared_array_attach,

	  METH_VARARGS,

	  METH_VARARGS | METH_KEYWORDS,

	  "Attach an existing numpy array from shared memory" },



	{ "delete", (PyCFunction) shared_array_delete,

src/shared_array.h

+1 −1
Original line number Diff line number Diff line
@@ -46,7 +46,7 @@ extern PyTypeObject PyArrayDescObject_Type; 


/* Main functions */

extern PyObject *shared_array_create(PyObject *self, PyObject *args, PyObject *kwds);

extern PyObject *shared_array_attach(PyObject *self, PyObject *args);

extern PyObject *shared_array_attach(PyObject *self, PyObject *args, PyObject *kwds);

extern PyObject *shared_array_delete(PyObject *self, PyObject *args);



/* SHM list function */

src/shared_array_attach.c

+22 −6
Original line number Diff line number Diff line
@@ -34,7 +34,7 @@ 
/*

 * Attach a numpy array from shared memory

 */

static PyObject *do_attach(const char *name)

static PyObject *do_attach(const char *name, int ro)

{

	struct array_meta *meta;

	int fd;
@@ -46,7 +46,7 @@ static PyObject *do_attach(const char *name) 
	npy_intp dims[NPY_MAXDIMS];



	/* Open the file */

	if ((fd = open_file(name, O_RDWR, 0)) < 0)

	if ((fd = open_file(name, ro ? O_RDONLY : O_RDWR, 0)) < 0)

		return PyErr_SetFromErrnoWithFilename(PyExc_OSError, name);



	/* Find the file size */
@@ -64,7 +64,9 @@ static PyObject *do_attach(const char *name) 
	map_size = file_info.st_size;



	/* Map the array data */

	map_addr = mmap(NULL, map_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

	map_addr = mmap(NULL, map_size,

	                PROT_READ | (ro ? 0 : PROT_WRITE),

	                MAP_SHARED, fd, 0);

	close(fd);

	if (map_addr == MAP_FAILED)

		return PyErr_SetFromErrnoWithFilename(PyExc_OSError, name);
@@ -102,6 +104,17 @@ static PyObject *do_attach(const char *name) 
	                    meta->typenum, NULL, map_addr, meta->itemsize,

	                    NPY_ARRAY_CARRAY, NULL);



	/* Optionally mark it read-only. */

	if (ro) {

		PyObject *res;



		res = PyObject_CallMethod(array, "setflags", "OOO",

		                          Py_False, Py_None, Py_None);

		if (res != NULL) {

			Py_DECREF(res);

		}

	}



	/* Attach MapOwner to the array */

	PyArray_SetBaseObject((PyArrayObject *) array, (PyObject *) map_owner);

	return array;
@@ -110,14 +123,17 @@ static PyObject *do_attach(const char *name) 
/*

 * Method: SharedArray.attach()

 */

PyObject *shared_array_attach(PyObject *self, PyObject *args)

PyObject *shared_array_attach(PyObject *self, PyObject *args, PyObject *kwds)

{

	char *kwlist[] = { "name", "ro", NULL };

	const char *name;

	int ro = 0;



	/* Parse the arguments */

	if (!PyArg_ParseTuple(args, "s", &name))

	if (!PyArg_ParseTupleAndKeywords(args, kwds, "s|p", kwlist,

	                                 &name, &ro))

		return NULL;



	/* Now do the real thing */

	return do_attach(name);

	return do_attach(name, ro);

}