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Issue #25318: Add _PyBytesWriter API 

Add a new private API to optimize Unicode encoders. It uses a small buffer
allocated on the stack and supports overallocation.

Use _PyBytesWriter API for UCS1 (ASCII and Latin1) and UTF-8 encoders. Enable
overallocation for the UTF-8 encoder with error handlers.

unicode_encode_ucs1(): initialize collend to collstart+1 to not check the
current character twice, we already know that it is not ASCII.
This commit is contained in:
Victor Stinner 2015-10-09 00:33:49 +02:00
parent 08ec6d9611
commit fdfbf78114
3 changed files with 269 additions and 133 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
Include/unicodeobject.h
View File

@ -908,7 +908,7 @@ typedef struct {
/* minimum character (default: 127, ASCII) */
Py_UCS4 min_char;
/* If non-zero, overallocate the buffer by 25% (default: 0). */
/* If non-zero, overallocate the buffer (default: 0). */
unsigned char overallocate;
/* If readonly is 1, buffer is a shared string (cannot be modified)

84
Objects/stringlib/codecs.h
View File

@ -263,10 +263,7 @@ STRINGLIB(utf8_encoder)(PyObject *unicode,
#define MAX_SHORT_UNICHARS 300 /* largest size we'll do on the stack */
Py_ssize_t i; /* index into s of next input byte */
PyObject *result; /* result string object */
char *p; /* next free byte in output buffer */
Py_ssize_t nallocated; /* number of result bytes allocated */
Py_ssize_t nneeded; /* number of result bytes needed */
#if STRINGLIB_SIZEOF_CHAR > 1
PyObject *error_handler_obj = NULL;
PyObject *exc = NULL;
@ -275,39 +272,25 @@ STRINGLIB(utf8_encoder)(PyObject *unicode,
#endif
#if STRINGLIB_SIZEOF_CHAR == 1
const Py_ssize_t max_char_size = 2;
char stackbuf[MAX_SHORT_UNICHARS * 2];
#elif STRINGLIB_SIZEOF_CHAR == 2
const Py_ssize_t max_char_size = 3;
char stackbuf[MAX_SHORT_UNICHARS * 3];
#else /* STRINGLIB_SIZEOF_CHAR == 4 */
const Py_ssize_t max_char_size = 4;
char stackbuf[MAX_SHORT_UNICHARS * 4];
#endif
_PyBytesWriter writer;
assert(size >= 0);
_PyBytesWriter_Init(&writer);
if (size <= MAX_SHORT_UNICHARS) {
/* Write into the stack buffer; nallocated can't overflow.
* At the end, we'll allocate exactly as much heap space as it
* turns out we need.
*/
nallocated = Py_SAFE_DOWNCAST(sizeof(stackbuf), size_t, int);
result = NULL; /* will allocate after we're done */
p = stackbuf;
}
else {
if (size > PY_SSIZE_T_MAX / max_char_size) {
/* integer overflow */
return PyErr_NoMemory();
}
/* Overallocate on the heap, and give the excess back at the end. */
nallocated = size * max_char_size;
result = PyBytes_FromStringAndSize(NULL, nallocated);
if (result == NULL)
return NULL;
p = PyBytes_AS_STRING(result);
if (size > PY_SSIZE_T_MAX / max_char_size) {
/* integer overflow */
return PyErr_NoMemory();
}
p = _PyBytesWriter_Alloc(&writer, size * max_char_size);
if (p == NULL)
return NULL;
for (i = 0; i < size;) {
Py_UCS4 ch = data[i++];
@ -338,6 +321,9 @@ STRINGLIB(utf8_encoder)(PyObject *unicode,
while ((endpos < size) && Py_UNICODE_IS_SURROGATE(data[endpos]))
endpos++;
/* Only overallocate the buffer if it's not the last write */
writer.overallocate = (endpos < size);
switch (error_handler)
{
case _Py_ERROR_REPLACE:
@ -387,29 +373,10 @@ STRINGLIB(utf8_encoder)(PyObject *unicode,
repsize = PyUnicode_GET_LENGTH(rep);
if (repsize > max_char_size) {
Py_ssize_t offset;
if (result == NULL)
offset = p - stackbuf;
else
offset = p - PyBytes_AS_STRING(result);
if (nallocated > PY_SSIZE_T_MAX - repsize + max_char_size) {
/* integer overflow */
PyErr_NoMemory();
p = _PyBytesWriter_Prepare(&writer, p,
repsize - max_char_size);
if (p == NULL)
goto error;
}
nallocated += repsize - max_char_size;
if (result != NULL) {
if (_PyBytes_Resize(&result, nallocated) < 0)
goto error;
} else {
result = PyBytes_FromStringAndSize(NULL, nallocated);
if (result == NULL)
goto error;
Py_MEMCPY(PyBytes_AS_STRING(result), stackbuf, offset);
}
p = PyBytes_AS_STRING(result) + offset;
}
if (PyBytes_Check(rep)) {
@ -437,6 +404,10 @@ STRINGLIB(utf8_encoder)(PyObject *unicode,
i = newpos;
}
/* If overallocation was disabled, ensure that it was the last
write. Otherwise, we missed an optimization */
assert(writer.overallocate || i == size);
}
else
#if STRINGLIB_SIZEOF_CHAR > 2
@ -461,31 +432,18 @@ STRINGLIB(utf8_encoder)(PyObject *unicode,
#endif /* STRINGLIB_SIZEOF_CHAR > 1 */
}
if (result == NULL) {
/* This was stack allocated. */
nneeded = p - stackbuf;
assert(nneeded <= nallocated);
result = PyBytes_FromStringAndSize(stackbuf, nneeded);
}
else {
/* Cut back to size actually needed. */
nneeded = p - PyBytes_AS_STRING(result);
assert(nneeded <= nallocated);
_PyBytes_Resize(&result, nneeded);
}
#if STRINGLIB_SIZEOF_CHAR > 1
Py_XDECREF(error_handler_obj);
Py_XDECREF(exc);
#endif
return result;
return _PyBytesWriter_Finish(&writer, p);
#if STRINGLIB_SIZEOF_CHAR > 1
error:
Py_XDECREF(rep);
Py_XDECREF(error_handler_obj);
Py_XDECREF(exc);
Py_XDECREF(result);
_PyBytesWriter_Dealloc(&writer);
return NULL;
#endif

316
Objects/unicodeobject.c
View File

@ -163,6 +163,14 @@ extern "C" {
*_to++ = (to_type) *_iter++; \
} while (0)
#ifdef MS_WINDOWS
/* On Windows, overallocate by 50% is the best factor */
# define OVERALLOCATE_FACTOR 2
#else
/* On Linux, overallocate by 25% is the best factor */
# define OVERALLOCATE_FACTOR 4
#endif
/* This dictionary holds all interned unicode strings. Note that references
to strings in this dictionary are *not* counted in the string's ob_refcnt.
When the interned string reaches a refcnt of 0 the string deallocation
@ -338,6 +346,216 @@ PyUnicode_GetMax(void)
#endif
}
/* The _PyBytesWriter structure is big: it contains an embeded "stack buffer".
A _PyBytesWriter variable must be declared at the end of variables in a
function to optimize the memory allocation on the stack. */
typedef struct {
/* bytes object */
PyObject *buffer;
/* Number of allocated size */
Py_ssize_t allocated;
/* Current size of the buffer (can be smaller than the allocated size) */
Py_ssize_t size;
/* If non-zero, overallocate the buffer (default: 0). */
int overallocate;
/* Stack buffer */
int use_stack_buffer;
char stack_buffer[512];
} _PyBytesWriter;
static void
_PyBytesWriter_Init(_PyBytesWriter *writer)
{
writer->buffer = NULL;
writer->allocated = 0;
writer->size = 0;
writer->overallocate = 0;
writer->use_stack_buffer = 0;
#ifdef Py_DEBUG
memset(writer->stack_buffer, 0xCB, sizeof(writer->stack_buffer));
#endif
}
static void
_PyBytesWriter_Dealloc(_PyBytesWriter *writer)
{
Py_CLEAR(writer->buffer);
}
static char*
_PyBytesWriter_AsString(_PyBytesWriter *writer)
{
if (!writer->use_stack_buffer) {
assert(writer->buffer != NULL);
return PyBytes_AS_STRING(writer->buffer);
}
else {
assert(writer->buffer == NULL);
return writer->stack_buffer;
}
}
Py_LOCAL_INLINE(Py_ssize_t)
_PyBytesWriter_GetPos(_PyBytesWriter *writer, char *str)
{
char *start = _PyBytesWriter_AsString(writer);
assert(str != NULL);
assert(str >= start);
return str - start;
}
Py_LOCAL_INLINE(void)
_PyBytesWriter_CheckConsistency(_PyBytesWriter *writer, char *str)
{
#ifdef Py_DEBUG
char *start, *end;
if (!writer->use_stack_buffer) {
assert(writer->buffer != NULL);
assert(PyBytes_CheckExact(writer->buffer));
assert(Py_REFCNT(writer->buffer) == 1);
}
else {
assert(writer->buffer == NULL);
}
start = _PyBytesWriter_AsString(writer);
assert(0 <= writer->size && writer->size <= writer->allocated);
/* the last byte must always be null */
assert(start[writer->allocated] == 0);
end = start + writer->allocated;
assert(str != NULL);
assert(start <= str && str <= end);
#endif
}
/* Add *size* bytes to the buffer.
str is the current pointer inside the buffer.
Return the updated current pointer inside the buffer.
Raise an exception and return NULL on error. */
static char*
_PyBytesWriter_Prepare(_PyBytesWriter *writer, char *str, Py_ssize_t size)
{
Py_ssize_t allocated, pos;
_PyBytesWriter_CheckConsistency(writer, str);
assert(size >= 0);
if (size == 0) {
/* nothing to do */
return str;
}
if (writer->size > PY_SSIZE_T_MAX - size) {
PyErr_NoMemory();
_PyBytesWriter_Dealloc(writer);
return NULL;
}
writer->size += size;
allocated = writer->allocated;
if (writer->size <= allocated)
return str;
allocated = writer->size;
if (writer->overallocate
&& allocated <= (PY_SSIZE_T_MAX - allocated / OVERALLOCATE_FACTOR)) {
/* overallocate to limit the number of realloc() */
allocated += allocated / OVERALLOCATE_FACTOR;
}
pos = _PyBytesWriter_GetPos(writer, str);
if (!writer->use_stack_buffer) {
/* Note: Don't use a bytearray object because the conversion from
byterray to bytes requires to copy all bytes. */
if (_PyBytes_Resize(&writer->buffer, allocated)) {
assert(writer->buffer == NULL);
return NULL;
}
}
else {
/* convert from stack buffer to bytes object buffer */
assert(writer->buffer == NULL);
writer->buffer = PyBytes_FromStringAndSize(NULL, allocated);
if (writer->buffer == NULL)
return NULL;
if (pos != 0) {
Py_MEMCPY(PyBytes_AS_STRING(writer->buffer),
writer->stack_buffer,
pos);
}
#ifdef Py_DEBUG
memset(writer->stack_buffer, 0xDB, sizeof(writer->stack_buffer));
#endif
writer->use_stack_buffer = 0;
}
writer->allocated = allocated;
str = _PyBytesWriter_AsString(writer) + pos;
_PyBytesWriter_CheckConsistency(writer, str);
return str;
}
/* Allocate the buffer to write size bytes.
Return the pointer to the beginning of buffer data.
Raise an exception and return NULL on error. */
static char*
_PyBytesWriter_Alloc(_PyBytesWriter *writer, Py_ssize_t size)
{
/* ensure that _PyBytesWriter_Alloc() is only called once */
assert(writer->size == 0 && writer->buffer == NULL);
assert(size >= 0);
writer->use_stack_buffer = 1;
#if Py_DEBUG
/* the last byte is reserved, it must be '\0' */
writer->stack_buffer[sizeof(writer->stack_buffer) - 1] = 0;
writer->allocated = sizeof(writer->stack_buffer) - 1;
#else
writer->allocated = sizeof(writer->stack_buffer);
#endif
return _PyBytesWriter_Prepare(writer, writer->stack_buffer, size);
}
/* Get the buffer content and reset the writer.
Return a bytes object.
Raise an exception and return NULL on error. */
static PyObject *
_PyBytesWriter_Finish(_PyBytesWriter *writer, char *str)
{
Py_ssize_t pos;
PyObject *result;
_PyBytesWriter_CheckConsistency(writer, str);
pos = _PyBytesWriter_GetPos(writer, str);
if (!writer->use_stack_buffer) {
if (pos != writer->allocated) {
if (_PyBytes_Resize(&writer->buffer, pos)) {
assert(writer->buffer == NULL);
return NULL;
}
}
result = writer->buffer;
writer->buffer = NULL;
}
else {
result = PyBytes_FromStringAndSize(writer->stack_buffer, pos);
}
return result;
}
#ifdef Py_DEBUG
int
_PyUnicode_CheckConsistency(PyObject *op, int check_content)
@ -6460,17 +6678,15 @@ unicode_encode_ucs1(PyObject *unicode,
Py_ssize_t pos=0, size;
int kind;
void *data;
/* output object */
PyObject *res;
/* pointer into the output */
char *str;
/* current output position */
Py_ssize_t ressize;
const char *encoding = (limit == 256) ? "latin-1" : "ascii";
const char *reason = (limit == 256) ? "ordinal not in range(256)" : "ordinal not in range(128)";
PyObject *error_handler_obj = NULL;
PyObject *exc = NULL;
_Py_error_handler error_handler = _Py_ERROR_UNKNOWN;
/* output object */
_PyBytesWriter writer;
if (PyUnicode_READY(unicode) == -1)
return NULL;
@ -6481,11 +6697,11 @@ unicode_encode_ucs1(PyObject *unicode,
replacements, if we need more, we'll resize */
if (size == 0)
return PyBytes_FromStringAndSize(NULL, 0);
res = PyBytes_FromStringAndSize(NULL, size);
if (res == NULL)
_PyBytesWriter_Init(&writer);
str = _PyBytesWriter_Alloc(&writer, size);
if (str == NULL)
return NULL;
str = PyBytes_AS_STRING(res);
ressize = size;
while (pos < size) {
Py_UCS4 ch = PyUnicode_READ(kind, data, pos);
@ -6499,15 +6715,18 @@ unicode_encode_ucs1(PyObject *unicode,
else {
Py_ssize_t requiredsize;
PyObject *repunicode;
Py_ssize_t repsize, newpos, respos, i;
Py_ssize_t repsize, newpos, i;
/* startpos for collecting unencodable chars */
Py_ssize_t collstart = pos;
Py_ssize_t collend = pos;
Py_ssize_t collend = collstart + 1;
/* find all unecodable characters */
while ((collend < size) && (PyUnicode_READ(kind, data, collend) >= limit))
++collend;
/* Only overallocate the buffer if it's not the last write */
writer.overallocate = (collend < size);
/* cache callback name lookup (if not done yet, i.e. it's the first error) */
if (error_handler == _Py_ERROR_UNKNOWN)
error_handler = get_error_handler(errors);
@ -6526,8 +6745,7 @@ unicode_encode_ucs1(PyObject *unicode,
break;
case _Py_ERROR_XMLCHARREFREPLACE:
respos = str - PyBytes_AS_STRING(res);
requiredsize = respos;
requiredsize = 0;
/* determine replacement size */
for (i = collstart; i < collend; ++i) {
Py_ssize_t incr;
@ -6553,17 +6771,11 @@ unicode_encode_ucs1(PyObject *unicode,
goto overflow;
requiredsize += incr;
}
if (requiredsize > PY_SSIZE_T_MAX - (size - collend))
goto overflow;
requiredsize += size - collend;
if (requiredsize > ressize) {
if (ressize <= PY_SSIZE_T_MAX/2 && requiredsize < 2*ressize)
requiredsize = 2*ressize;
if (_PyBytes_Resize(&res, requiredsize))
goto onError;
str = PyBytes_AS_STRING(res) + respos;
ressize = requiredsize;
}
str = _PyBytesWriter_Prepare(&writer, str, requiredsize-1);
if (str == NULL)
goto onError;
/* generate replacement */
for (i = collstart; i < collend; ++i) {
str += sprintf(str, "&#%d;", PyUnicode_READ(kind, data, i));
@ -6598,20 +6810,9 @@ unicode_encode_ucs1(PyObject *unicode,
if (PyBytes_Check(repunicode)) {
/* Directly copy bytes result to output. */
repsize = PyBytes_Size(repunicode);
if (repsize > 1) {
/* Make room for all additional bytes. */
respos = str - PyBytes_AS_STRING(res);
if (ressize > PY_SSIZE_T_MAX - repsize - 1) {
Py_DECREF(repunicode);
goto overflow;
}
if (_PyBytes_Resize(&res, ressize+repsize-1)) {
Py_DECREF(repunicode);
goto onError;
}
str = PyBytes_AS_STRING(res) + respos;
ressize += repsize-1;
}
str = _PyBytesWriter_Prepare(&writer, str, repsize-1);
if (str == NULL)
goto onError;
memcpy(str, PyBytes_AsString(repunicode), repsize);
str += repsize;
pos = newpos;
@ -6622,24 +6823,11 @@ unicode_encode_ucs1(PyObject *unicode,
/* need more space? (at least enough for what we
have+the replacement+the rest of the string, so
we won't have to check space for encodable characters) */
respos = str - PyBytes_AS_STRING(res);
repsize = PyUnicode_GET_LENGTH(repunicode);
requiredsize = respos;
if (requiredsize > PY_SSIZE_T_MAX - repsize)
goto overflow;
requiredsize += repsize;
if (requiredsize > PY_SSIZE_T_MAX - (size - collend))
goto overflow;
requiredsize += size - collend;
if (requiredsize > ressize) {
if (ressize <= PY_SSIZE_T_MAX/2 && requiredsize < 2*ressize)
requiredsize = 2*ressize;
if (_PyBytes_Resize(&res, requiredsize)) {
Py_DECREF(repunicode);
if (repsize > 1) {
str = _PyBytesWriter_Prepare(&writer, str, repsize-1);
if (str == NULL)
goto onError;
}
str = PyBytes_AS_STRING(res) + respos;
ressize = requiredsize;
}
/* check if there is anything unencodable in the replacement
@ -6657,26 +6845,23 @@ unicode_encode_ucs1(PyObject *unicode,
pos = newpos;
Py_DECREF(repunicode);
}
/* If overallocation was disabled, ensure that it was the last
write. Otherwise, we missed an optimization */
assert(writer.overallocate || pos == size);
}
}
/* Resize if we allocated to much */
size = str - PyBytes_AS_STRING(res);
if (size < ressize) { /* If this falls res will be NULL */
assert(size >= 0);
if (_PyBytes_Resize(&res, size) < 0)
goto onError;
}
Py_XDECREF(error_handler_obj);
Py_XDECREF(exc);
return res;
return _PyBytesWriter_Finish(&writer, str);
overflow:
PyErr_SetString(PyExc_OverflowError,
"encoded result is too long for a Python string");
onError:
Py_XDECREF(res);
_PyBytesWriter_Dealloc(&writer);
Py_XDECREF(error_handler_obj);
Py_XDECREF(exc);
return NULL;
@ -13366,13 +13551,6 @@ int
_PyUnicodeWriter_PrepareInternal(_PyUnicodeWriter *writer,
Py_ssize_t length, Py_UCS4 maxchar)
{
#ifdef MS_WINDOWS
/* On Windows, overallocate by 50% is the best factor */
# define OVERALLOCATE_FACTOR 2
#else
/* On Linux, overallocate by 25% is the best factor */
# define OVERALLOCATE_FACTOR 4
#endif
Py_ssize_t newlen;
PyObject *newbuffer;