[Python-Dev] test_mmap failing? (original) (raw)

Tim Peters tim.one@home.com
Wed, 9 May 2001 22:54:45 -0400

I checked in a change to mmapmodule.c earlier today, to close a patch complaining about unused vrbl warnings.

Here's the changed routine before ("value" is unused):

mmap_read_byte_method(mmap_object *self, PyObject *args) { char value; char *where; CHECK_VALID(NULL); if (!PyArg_ParseTuple(args, ":read_byte")) return NULL; if (self->pos < self->size) { where = self->data + self->pos; value = (char) *(where); self->pos += 1; return Py_BuildValue("c", (char) *(where)); } else { PyErr_SetString (PyExc_ValueError, "read byte out of range"); return NULL; } }

and after:

mmap_read_byte_method(mmap_object *self, PyObject *args) { CHECK_VALID(NULL); if (!PyArg_ParseTuple(args, ":read_byte")) return NULL; if (self->pos < self->size) { char value = self->data[self->pos]; self->pos += 1; return Py_BuildValue("c", value); } else { PyErr_SetString (PyExc_ValueError, "read byte out of range"); return NULL; } }

I'll be damned if I can see any semantic difference, and test_mmap worked fine on Windows after the change. But Fred reported:

""" the fix introduced breakage on Linux (kernel 2.2.17):

cj42289-a(.../python/linux-beowolf); ./python ../Lib/test/regrtest.py -v test_mmap test_mmap test_mmap test test_mmap crashed -- exceptions.IOError: [Errno 22] Invalid argument Traceback (most recent call last): File "../Lib/test/regrtest.py", line 246, in runtest import(test, globals(), locals(), []) File "../Lib/test/test_mmap.py", line 124, in ? test_both() File "../Lib/test/test_mmap.py", line 14, in test_both f.write('\0'* PAGESIZE) IOError: [Errno 22] Invalid argument 1 test failed: test_mmap """

However, at the point that's failing, test_mmap hasn't even created an mmap'ed file yet, let alone tried to read from it. The only thing test_mmap did so far is (the first comment is bogus -- that's the builtin Python open() function):

# Create an mmap'ed file   # THIS IS A BOGUS COMMENT
f = open('foo', 'w+')

# Write 2 pages worth of data to the file
f.write('\0'* PAGESIZE)    # THIS IS THE LINE IT'S DYING ON

But having suffered too many "impossible problems" the last 36 hours, my confidence is shot <0.93 wink>. Is test_mmap failing for anyone else under current CVS? Fred, are you sure it fails for you -- if so, does the problem actually go away if you revert mmapmodule.c?

looking-for-sense-in-all-the-wrong-places-ly y'rs - tim