diff options
| -rw-r--r-- | Lib/_pyio.py | 22 | ||||
| -rw-r--r-- | Misc/NEWS.d/next/Core and Builtins/2024-06-19-19-54-35.gh-issue-120754.uF29sj.rst | 1 | ||||
| -rw-r--r-- | Modules/_io/fileio.c | 70 |
3 files changed, 60 insertions, 33 deletions
diff --git a/Lib/_pyio.py b/Lib/_pyio.py index 7d298e1..75b5ad1 100644 --- a/Lib/_pyio.py +++ b/Lib/_pyio.py @@ -1577,6 +1577,7 @@ class FileIO(RawIOBase): self._blksize = getattr(fdfstat, 'st_blksize', 0) if self._blksize <= 1: self._blksize = DEFAULT_BUFFER_SIZE + self._estimated_size = fdfstat.st_size if _setmode: # don't translate newlines (\r\n <=> \n) @@ -1654,14 +1655,18 @@ class FileIO(RawIOBase): """ self._checkClosed() self._checkReadable() - bufsize = DEFAULT_BUFFER_SIZE - try: - pos = os.lseek(self._fd, 0, SEEK_CUR) - end = os.fstat(self._fd).st_size - if end >= pos: - bufsize = end - pos + 1 - except OSError: - pass + if self._estimated_size <= 0: + bufsize = DEFAULT_BUFFER_SIZE + else: + bufsize = self._estimated_size + 1 + + if self._estimated_size > 65536: + try: + pos = os.lseek(self._fd, 0, SEEK_CUR) + if self._estimated_size >= pos: + bufsize = self._estimated_size - pos + 1 + except OSError: + pass result = bytearray() while True: @@ -1737,6 +1742,7 @@ class FileIO(RawIOBase): if size is None: size = self.tell() os.ftruncate(self._fd, size) + self._estimated_size = size return size def close(self): diff --git a/Misc/NEWS.d/next/Core and Builtins/2024-06-19-19-54-35.gh-issue-120754.uF29sj.rst b/Misc/NEWS.d/next/Core and Builtins/2024-06-19-19-54-35.gh-issue-120754.uF29sj.rst new file mode 100644 index 0000000..46481d8 --- /dev/null +++ b/Misc/NEWS.d/next/Core and Builtins/2024-06-19-19-54-35.gh-issue-120754.uF29sj.rst @@ -0,0 +1 @@ +Reduce the number of system calls invoked when reading a whole file (ex. ``open('a.txt').read()``). For a sample program that reads the contents of the 400+ ``.rst`` files in the cpython repository ``Doc`` folder, there is an over 10% reduction in system call count. diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c index b5129ff..d5bf328 100644 --- a/Modules/_io/fileio.c +++ b/Modules/_io/fileio.c @@ -54,6 +54,9 @@ # define SMALLCHUNK BUFSIZ #endif +/* Size at which a buffer is considered "large" and behavior should change to + avoid excessive memory allocation */ +#define LARGE_BUFFER_CUTOFF_SIZE 65536 /*[clinic input] module _io @@ -72,6 +75,7 @@ typedef struct { unsigned int closefd : 1; char finalizing; unsigned int blksize; + Py_off_t estimated_size; PyObject *weakreflist; PyObject *dict; } fileio; @@ -196,6 +200,7 @@ fileio_new(PyTypeObject *type, PyObject *args, PyObject *kwds) self->appending = 0; self->seekable = -1; self->blksize = 0; + self->estimated_size = -1; self->closefd = 1; self->weakreflist = NULL; } @@ -482,6 +487,9 @@ _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 */ + if (fdfstat.st_size < PY_SSIZE_T_MAX) { + self->estimated_size = (Py_off_t)fdfstat.st_size; + } } #if defined(MS_WINDOWS) || defined(__CYGWIN__) @@ -684,7 +692,7 @@ new_buffersize(fileio *self, size_t currentsize) 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) + if (currentsize > LARGE_BUFFER_CUTOFF_SIZE) addend = currentsize >> 3; else addend = 256 + currentsize; @@ -707,43 +715,56 @@ static PyObject * _io_FileIO_readall_impl(fileio *self) /*[clinic end generated code: output=faa0292b213b4022 input=dbdc137f55602834]*/ { - struct _Py_stat_struct status; Py_off_t pos, end; PyObject *result; Py_ssize_t bytes_read = 0; Py_ssize_t n; size_t bufsize; - int fstat_result; - if (self->fd < 0) + if (self->fd < 0) { return err_closed(); + } - Py_BEGIN_ALLOW_THREADS - _Py_BEGIN_SUPPRESS_IPH -#ifdef MS_WINDOWS - pos = _lseeki64(self->fd, 0L, SEEK_CUR); -#else - pos = lseek(self->fd, 0L, SEEK_CUR); -#endif - _Py_END_SUPPRESS_IPH - fstat_result = _Py_fstat_noraise(self->fd, &status); - Py_END_ALLOW_THREADS - - if (fstat_result == 0) - end = status.st_size; - else - end = (Py_off_t)-1; - - if (end > 0 && end >= pos && pos >= 0 && end - pos < PY_SSIZE_T_MAX) { + end = self->estimated_size; + if (end <= 0) { + /* Use a default size and resize as needed. */ + bufsize = SMALLCHUNK; + } + else { /* 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; + if (end > _PY_READ_MAX - 1) { + bufsize = _PY_READ_MAX; + } + else { + bufsize = (size_t)end + 1; + } + + /* While a lot of code does open().read() to get the whole contents + of a file it is possible a caller seeks/reads a ways into the file + then calls readall() to get the rest, which would result in allocating + more than required. Guard against that for larger files where we expect + the I/O time to dominate anyways while keeping small files fast. */ + if (bufsize > LARGE_BUFFER_CUTOFF_SIZE) { + Py_BEGIN_ALLOW_THREADS + _Py_BEGIN_SUPPRESS_IPH +#ifdef MS_WINDOWS + pos = _lseeki64(self->fd, 0L, SEEK_CUR); +#else + pos = lseek(self->fd, 0L, SEEK_CUR); +#endif + _Py_END_SUPPRESS_IPH + Py_END_ALLOW_THREADS + + if (end >= pos && pos >= 0 && (end - pos) < (_PY_READ_MAX - 1)) { + bufsize = (size_t)(end - pos) + 1; + } + } } + result = PyBytes_FromStringAndSize(NULL, bufsize); if (result == NULL) return NULL; @@ -783,7 +804,6 @@ _io_FileIO_readall_impl(fileio *self) return NULL; } bytes_read += n; - pos += n; } if (PyBytes_GET_SIZE(result) > bytes_read) { |