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bpo-45944: Avoid calling isatty() for most open() calls #29870

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bpo-45944: Avoid calling isatty() for most open() calls #29870

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bpo-45944: Avoid calling isatty() for most open() calls
collinanderson Dec 1, 2021
a4911db
Merge branch 'main' into 45944
serhiy-storchaka Nov 28, 2023
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1 change: 1 addition & 0 deletions Include/internal/pycore_global_objects_fini_generated.h
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1 change: 1 addition & 0 deletions Include/internal/pycore_global_strings.h
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Original file line number Diff line number Diff line change
Expand Up @@ -260,6 +260,7 @@ struct _Py_global_strings {
STRUCT_FOR_ID(_restype_)
STRUCT_FOR_ID(_showwarnmsg)
STRUCT_FOR_ID(_shutdown)
STRUCT_FOR_ID(_size)
STRUCT_FOR_ID(_slotnames)
STRUCT_FOR_ID(_strptime_datetime)
STRUCT_FOR_ID(_swappedbytes_)
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1 change: 1 addition & 0 deletions Include/internal/pycore_runtime_init_generated.h
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3 changes: 3 additions & 0 deletions Include/internal/pycore_unicodeobject_generated.h
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3 changes: 2 additions & 1 deletion Lib/_pyio.py
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Original file line number Diff line number Diff line change
Expand Up @@ -238,7 +238,7 @@ def open(file, mode="r", buffering=-1, encoding=None, errors=None,
result = raw
try:
line_buffering = False
if buffering == 1 or buffering < 0 and raw.isatty():
if buffering == 1 or buffering < 0 and getattr(raw, '_size', 0) == 0 and raw.isatty():
buffering = -1
line_buffering = True
if buffering < 0:
Expand Down Expand Up @@ -1571,6 +1571,7 @@ def __init__(self, file, mode='r', closefd=True, opener=None):
self._blksize = getattr(fdfstat, 'st_blksize', 0)
if self._blksize <= 1:
self._blksize = DEFAULT_BUFFER_SIZE
self._size = fdfstat.st_size

if _setmode:
# don't translate newlines (\r\n <=> \n)
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11 changes: 11 additions & 0 deletions Modules/_io/_iomodule.c
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Expand Up @@ -209,6 +209,7 @@ _io_open_impl(PyObject *module, PyObject *file, const char *mode,

char rawmode[6], *m;
int line_buffering, is_number, isatty = 0;
__int64_t size = 0;
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Suggested change
__int64_t size = 0;
Py_ssize_t size = 0;


PyObject *raw, *modeobj = NULL, *buffer, *wrapper, *result = NULL, *path_or_fd = NULL;

Expand Down Expand Up @@ -346,6 +347,16 @@ _io_open_impl(PyObject *module, PyObject *file, const char *mode,

/* buffering */
if (buffering < 0) {
PyObject *size_obj;
size_obj = PyObject_GetAttr(raw, &_Py_ID(_size));
if (size_obj == NULL)
goto error;
size = PyLong_AsLongLong(size_obj);
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size = PyLong_AsLongLong(size_obj);
size = PyLong_AsSsize_t(size_obj);

Py_DECREF(size_obj);
if (size == -1 && PyErr_Occurred())
goto error;
}
if (buffering < 0 && size == 0) {
PyObject *res = PyObject_CallMethodNoArgs(raw, &_Py_ID(isatty));
if (res == NULL)
goto error;
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4 changes: 4 additions & 0 deletions Modules/_io/fileio.c
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Original file line number Diff line number Diff line change
Expand Up @@ -72,6 +72,7 @@ typedef struct {
unsigned int closefd : 1;
char finalizing;
unsigned int blksize;
__int64_t size;
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Suggested change
__int64_t size;
Py_ssize_t size;

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It should be off_t. The file size can exceed the Py_ssize_t range.

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You are right! size handling depends on platform and support for large file support. You can copy the approach from posixmodule.c:

#ifdef MS_WINDOWS
    typedef long long Py_off_t;
#else
    typedef off_t Py_off_t;
#endif

#ifdef HAVE_LARGEFILE_SUPPORT
    size = (Py_off_t)PyLong_AsLongLong(arg);
#else
    size = (Py_off_t)PyLong_AsLong(arg);
#endif

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It is too complicated, we need to duplicate this in several files. But it may be simpler if only cache the boolean result (st_size == 0 or S_IFCHR()) as _maybeatty. Then the size of off_t does not matter.

PyObject *weakreflist;
PyObject *dict;
} fileio;
Expand Down Expand Up @@ -196,6 +197,7 @@ fileio_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
self->appending = 0;
self->seekable = -1;
self->blksize = 0;
self->size = 0;
self->closefd = 1;
self->weakreflist = NULL;
}
Expand Down Expand Up @@ -475,6 +477,7 @@ _io_FileIO___init___impl(fileio *self, PyObject *nameobj, const char *mode,
if (fdfstat.st_blksize > 1)
self->blksize = fdfstat.st_blksize;
#endif /* HAVE_STRUCT_STAT_ST_BLKSIZE */
self->size = fdfstat.st_size;
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Suggested change
self->size = fdfstat.st_size;
self->size = fdfstat.st_size;

}

#if defined(MS_WINDOWS) || defined(__CYGWIN__)
Expand Down Expand Up @@ -1205,6 +1208,7 @@ static PyGetSetDef fileio_getsetlist[] = {

static PyMemberDef fileio_members[] = {
{"_blksize", Py_T_UINT, offsetof(fileio, blksize), 0},
{"_size", T_UINT, offsetof(fileio, size), 0},
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Suggested change
{"_size", T_UINT, offsetof(fileio, size), 0},
{"_size", T_PYSSIZET, offsetof(fileio, size), 0},

{"_finalizing", Py_T_BOOL, offsetof(fileio, finalizing), 0},
{"__weaklistoffset__", Py_T_PYSSIZET, offsetof(fileio, weakreflist), Py_READONLY},
{"__dictoffset__", Py_T_PYSSIZET, offsetof(fileio, dict), Py_READONLY},
Expand Down