traverseda
/
cpython
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

Issue #15758: Fix FileIO.readall() so it no longer has O(n**2) complexity.

This commit is contained in:
Richard Oudkerk 2013-05-17 23:34:42 +01:00
parent a29ac45200
commit af7260e81a
2 changed files with 55 additions and 67 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
Misc/NEWS
View File

@ -91,6 +91,8 @@ Core and Builtins
Library
-------
- Issue #15758: Fix FileIO.readall() so it no longer has O(n**2) complexity.
- Issue #14596: The struct.Struct() objects now use more compact implementation.
- Issue #17981: Closed socket on error in SysLogHandler.

120
Modules/_io/fileio.c
View File

@ -556,33 +556,27 @@ fileio_readinto(fileio *self, PyObject *args)
return PyLong_FromSsize_t(n);
}
#ifndef HAVE_FSTAT
static PyObject *
fileio_readall(fileio *self)
{
_Py_IDENTIFIER(readall);
return _PyObject_CallMethodId((PyObject*)&PyRawIOBase_Type,
&PyId_readall, "O", self);
}
#else
static size_t
new_buffersize(fileio *self, size_t currentsize
#ifdef HAVE_FSTAT
, Py_off_t pos, Py_off_t end
#endif
)
new_buffersize(fileio *self, size_t currentsize)
{
size_t addend;
#ifdef HAVE_FSTAT
if (end != (Py_off_t)-1) {
/* Files claiming a size smaller than SMALLCHUNK may
actually be streaming pseudo-files. In this case, we
apply the more aggressive algorithm below.
*/
if (end >= SMALLCHUNK && end >= pos && pos >= 0) {
/* Add 1 so if the file were to grow we'd notice. */
Py_off_t bufsize = currentsize + end - pos + 1;
if (bufsize < PY_SSIZE_T_MAX)
return (size_t)bufsize;
else
return PY_SSIZE_T_MAX;
}
}
#endif
/* Expand the buffer by an amount proportional to the current size,
giving us amortized linear-time behavior. For bigger sizes, use a
less-than-double growth factor to avoid excessive allocation. */
assert(currentsize <= PY_SSIZE_T_MAX);
if (currentsize > 65536)
addend = currentsize >> 3;
else
@ -596,25 +590,18 @@ new_buffersize(fileio *self, size_t currentsize
static PyObject *
fileio_readall(fileio *self)
{
#ifdef HAVE_FSTAT
struct stat st;
Py_off_t pos, end;
#endif
PyObject *result;
Py_ssize_t total = 0;
Py_ssize_t bytes_read = 0;
Py_ssize_t n;
size_t newsize;
size_t bufsize;
if (self->fd < 0)
return err_closed();
if (!_PyVerify_fd(self->fd))
return PyErr_SetFromErrno(PyExc_IOError);
result = PyBytes_FromStringAndSize(NULL, SMALLCHUNK);
if (result == NULL)
return NULL;
#ifdef HAVE_FSTAT
#if defined(MS_WIN64) || defined(MS_WINDOWS)
pos = _lseeki64(self->fd, 0L, SEEK_CUR);
#else
@ -624,44 +611,46 @@ fileio_readall(fileio *self)
end = st.st_size;
else
end = (Py_off_t)-1;
#endif
while (1) {
#ifdef HAVE_FSTAT
newsize = new_buffersize(self, total, pos, end);
#else
newsize = new_buffersize(self, total);
#endif
if (newsize > PY_SSIZE_T_MAX || newsize <= 0) {
PyErr_SetString(PyExc_OverflowError,
"unbounded read returned more bytes "
"than a Python string can hold ");
Py_DECREF(result);
return NULL;
}
if (PyBytes_GET_SIZE(result) < (Py_ssize_t)newsize) {
if (_PyBytes_Resize(&result, newsize) < 0) {
if (total == 0) {
Py_DECREF(result);
if (end > 0 && end >= pos && pos >= 0 && end - pos < PY_SSIZE_T_MAX) {
/* This is probably a real file, so we try to allocate a
buffer one byte larger than the rest of the file. If the
calculation is right then we should get EOF without having
to enlarge the buffer. */
bufsize = (size_t)(end - pos + 1);
} else {
bufsize = SMALLCHUNK;
}
result = PyBytes_FromStringAndSize(NULL, bufsize);
if (result == NULL)
return NULL;
while (1) {
if (bytes_read >= (Py_ssize_t)bufsize) {
bufsize = new_buffersize(self, bytes_read);
if (bufsize > PY_SSIZE_T_MAX || bufsize <= 0) {
PyErr_SetString(PyExc_OverflowError,
"unbounded read returned more bytes "
"than a Python string can hold ");
Py_DECREF(result);
return NULL;
}
if (PyBytes_GET_SIZE(result) < (Py_ssize_t)bufsize) {
if (_PyBytes_Resize(&result, bufsize) < 0)
return NULL;
}
PyErr_Clear();
break;
}
}
Py_BEGIN_ALLOW_THREADS
errno = 0;
n = newsize - total;
n = bufsize - bytes_read;
#if defined(MS_WIN64) || defined(MS_WINDOWS)
if (n > INT_MAX)
n = INT_MAX;
n = read(self->fd,
PyBytes_AS_STRING(result) + total,
(int)n);
n = read(self->fd, PyBytes_AS_STRING(result) + bytes_read, (int)n);
#else
n = read(self->fd,
PyBytes_AS_STRING(result) + total,
n);
n = read(self->fd, PyBytes_AS_STRING(result) + bytes_read, n);
#endif
Py_END_ALLOW_THREADS
if (n == 0)
@ -674,7 +663,7 @@ fileio_readall(fileio *self)
}
continue;
}
if (total > 0)
if (bytes_read > 0)
break;
if (errno == EAGAIN) {
Py_DECREF(result);
@ -684,22 +673,19 @@ fileio_readall(fileio *self)
PyErr_SetFromErrno(PyExc_IOError);
return NULL;
}
total += n;
#ifdef HAVE_FSTAT
bytes_read += n;
pos += n;
#endif
}
if (PyBytes_GET_SIZE(result) > total) {
if (_PyBytes_Resize(&result, total) < 0) {
/* This should never happen, but just in case */
Py_DECREF(result);
if (PyBytes_GET_SIZE(result) > bytes_read) {
if (_PyBytes_Resize(&result, bytes_read) < 0)
return NULL;
}
}
return result;
}
#endif /* HAVE_FSTAT */
static PyObject *
fileio_read(fileio *self, PyObject *args)
{