bpo-41486: Faster bz2/lzma/zlib via new output buffering (GH-21740)

Faster bz2/lzma/zlib via new output buffering.
Also adds .readall() function to _compression.DecompressReader class
to take best advantage of this in the consume-all-output at once scenario.

Often a 5-20% speedup in common scenarios due to less data copying.

Contributed by Ma Lin.

Author: Ma Lin

Doc/whatsnew/3.10.rst

@@ -1243,6 +1243,12 @@ Optimizations
   for more details. (Contributed by Victor Stinner and Pablo Galindo in
   :issue:`38980`.)
 
+* Use a new output buffer management code for :mod:`bz2` / :mod:`lzma` /
+  :mod:`zlib` modules, and add ``.readall()`` function to
+  ``_compression.DecompressReader`` class. bz2 decompression 1.09x ~ 1.17x
+  faster, lzma decompression 1.20x ~ 1.32x faster, ``GzipFile.read(-1)`` 1.11x
+  ~ 1.18x faster. (Contributed by Ma Lin, reviewed by Gregory P. Smith, in :issue:`41486`)
+
 * Function parameters and their annotations are no longer computed at runtime,
   but rather at compilation time.  They are stored as a tuple of strings at the
   bytecode level. It is now around 2 times faster to create a function with

Include/internal/pycore_blocks_output_buffer.h

@@ -0,0 +1,317 @@
+/*
+   _BlocksOutputBuffer is used to maintain an output buffer
+   that has unpredictable size. Suitable for compression/decompression
+   API (bz2/lzma/zlib) that has stream->next_out and stream->avail_out:
+
+        stream->next_out:  point to the next output position.
+        stream->avail_out: the number of available bytes left in the buffer.
+
+   It maintains a list of bytes object, so there is no overhead of resizing
+   the buffer.
+
+   Usage:
+
+   1, Initialize the struct instance like this:
+        _BlocksOutputBuffer buffer = {.list = NULL};
+      Set .list to NULL for _BlocksOutputBuffer_OnError()
+
+   2, Initialize the buffer use one of these functions:
+        _BlocksOutputBuffer_InitAndGrow()
+        _BlocksOutputBuffer_InitWithSize()
+
+   3, If (avail_out == 0), grow the buffer:
+        _BlocksOutputBuffer_Grow()
+
+   4, Get the current outputted data size:
+        _BlocksOutputBuffer_GetDataSize()
+
+   5, Finish the buffer, and return a bytes object:
+        _BlocksOutputBuffer_Finish()
+
+   6, Clean up the buffer when an error occurred:
+        _BlocksOutputBuffer_OnError()
+*/
+
+#ifndef Py_INTERNAL_BLOCKS_OUTPUT_BUFFER_H
+#define Py_INTERNAL_BLOCKS_OUTPUT_BUFFER_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "Python.h"
+
+typedef struct {
+    // List of bytes objects
+    PyObject *list;
+    // Number of whole allocated size
+    Py_ssize_t allocated;
+    // Max length of the buffer, negative number means unlimited length.
+    Py_ssize_t max_length;
+} _BlocksOutputBuffer;
+
+static const char unable_allocate_msg[] = "Unable to allocate output buffer.";
+
+/* In 32-bit build, the max block size should <= INT32_MAX. */
+#define OUTPUT_BUFFER_MAX_BLOCK_SIZE (256*1024*1024)
+
+/* Block size sequence */
+#define KB (1024)
+#define MB (1024*1024)
+const Py_ssize_t BUFFER_BLOCK_SIZE[] =
+    { 32*KB, 64*KB, 256*KB, 1*MB, 4*MB, 8*MB, 16*MB, 16*MB,
+      32*MB, 32*MB, 32*MB, 32*MB, 64*MB, 64*MB, 128*MB, 128*MB,
+      OUTPUT_BUFFER_MAX_BLOCK_SIZE };
+#undef KB
+#undef MB
+
+/* According to the block sizes defined by BUFFER_BLOCK_SIZE, the whole
+   allocated size growth step is:
+    1   32 KB       +32 KB
+    2   96 KB       +64 KB
+    3   352 KB      +256 KB
+    4   1.34 MB     +1 MB
+    5   5.34 MB     +4 MB
+    6   13.34 MB    +8 MB
+    7   29.34 MB    +16 MB
+    8   45.34 MB    +16 MB
+    9   77.34 MB    +32 MB
+    10  109.34 MB   +32 MB
+    11  141.34 MB   +32 MB
+    12  173.34 MB   +32 MB
+    13  237.34 MB   +64 MB
+    14  301.34 MB   +64 MB
+    15  429.34 MB   +128 MB
+    16  557.34 MB   +128 MB
+    17  813.34 MB   +256 MB
+    18  1069.34 MB  +256 MB
+    19  1325.34 MB  +256 MB
+    20  1581.34 MB  +256 MB
+    21  1837.34 MB  +256 MB
+    22  2093.34 MB  +256 MB
+    ...
+*/
+
+/* Initialize the buffer, and grow the buffer.
+
+   max_length: Max length of the buffer, -1 for unlimited length.
+
+   On success, return allocated size (>=0)
+   On failure, return -1
+*/
+static inline Py_ssize_t
+_BlocksOutputBuffer_InitAndGrow(_BlocksOutputBuffer *buffer,
+                                const Py_ssize_t max_length,
+                                void **next_out)
+{
+    PyObject *b;
+    Py_ssize_t block_size;
+
+    // ensure .list was set to NULL
+    assert(buffer->list == NULL);
+
+    // get block size
+    if (0 <= max_length && max_length < BUFFER_BLOCK_SIZE[0]) {
+        block_size = max_length;
+    } else {
+        block_size = BUFFER_BLOCK_SIZE[0];
+    }
+
+    // the first block
+    b = PyBytes_FromStringAndSize(NULL, block_size);
+    if (b == NULL) {
+        return -1;
+    }
+
+    // create the list
+    buffer->list = PyList_New(1);
+    if (buffer->list == NULL) {
+        Py_DECREF(b);
+        return -1;
+    }
+    PyList_SET_ITEM(buffer->list, 0, b);
+
+    // set variables
+    buffer->allocated = block_size;
+    buffer->max_length = max_length;
+
+    *next_out = PyBytes_AS_STRING(b);
+    return block_size;
+}
+
+/* Initialize the buffer, with an initial size.
+
+   Check block size limit in the outer wrapper function. For example, some libs
+   accept UINT32_MAX as the maximum block size, then init_size should <= it.
+
+   On success, return allocated size (>=0)
+   On failure, return -1
+*/
+static inline Py_ssize_t
+_BlocksOutputBuffer_InitWithSize(_BlocksOutputBuffer *buffer,
+                                 const Py_ssize_t init_size,
+                                 void **next_out)
+{
+    PyObject *b;
+
+    // ensure .list was set to NULL
+    assert(buffer->list == NULL);
+
+    // the first block
+    b = PyBytes_FromStringAndSize(NULL, init_size);
+    if (b == NULL) {
+        PyErr_SetString(PyExc_MemoryError, unable_allocate_msg);
+        return -1;
+    }
+
+    // create the list
+    buffer->list = PyList_New(1);
+    if (buffer->list == NULL) {
+        Py_DECREF(b);
+        return -1;
+    }
+    PyList_SET_ITEM(buffer->list, 0, b);
+
+    // set variables
+    buffer->allocated = init_size;
+    buffer->max_length = -1;
+
+    *next_out = PyBytes_AS_STRING(b);
+    return init_size;
+}
+
+/* Grow the buffer. The avail_out must be 0, please check it before calling.
+
+   On success, return allocated size (>=0)
+   On failure, return -1
+*/
+static inline Py_ssize_t
+_BlocksOutputBuffer_Grow(_BlocksOutputBuffer *buffer,
+                         void **next_out,
+                         const Py_ssize_t avail_out)
+{
+    PyObject *b;
+    const Py_ssize_t list_len = Py_SIZE(buffer->list);
+    Py_ssize_t block_size;
+
+    // ensure no gaps in the data
+    if (avail_out != 0) {
+        PyErr_SetString(PyExc_SystemError,
+                        "avail_out is non-zero in _BlocksOutputBuffer_Grow().");
+        return -1;
+    }
+
+    // get block size
+    if (list_len < (Py_ssize_t) Py_ARRAY_LENGTH(BUFFER_BLOCK_SIZE)) {
+        block_size = BUFFER_BLOCK_SIZE[list_len];
+    } else {
+        block_size = BUFFER_BLOCK_SIZE[Py_ARRAY_LENGTH(BUFFER_BLOCK_SIZE) - 1];
+    }
+
+    // check max_length
+    if (buffer->max_length >= 0) {
+        // if (rest == 0), should not grow the buffer.
+        Py_ssize_t rest = buffer->max_length - buffer->allocated;
+        assert(rest > 0);
+
+        // block_size of the last block
+        if (block_size > rest) {
+            block_size = rest;
+        }
+    }
+
+    // check buffer->allocated overflow
+    if (block_size > PY_SSIZE_T_MAX - buffer->allocated) {
+        PyErr_SetString(PyExc_MemoryError, unable_allocate_msg);
+        return -1;
+    }
+
+    // create the block
+    b = PyBytes_FromStringAndSize(NULL, block_size);
+    if (b == NULL) {
+        PyErr_SetString(PyExc_MemoryError, unable_allocate_msg);
+        return -1;
+    }
+    if (PyList_Append(buffer->list, b) < 0) {
+        Py_DECREF(b);
+        return -1;
+    }
+    Py_DECREF(b);
+
+    // set variables
+    buffer->allocated += block_size;
+
+    *next_out = PyBytes_AS_STRING(b);
+    return block_size;
+}
+
+/* Return the current outputted data size. */
+static inline Py_ssize_t
+_BlocksOutputBuffer_GetDataSize(_BlocksOutputBuffer *buffer,
+                                const Py_ssize_t avail_out)
+{
+    return buffer->allocated - avail_out;
+}
+
+/* Finish the buffer.
+
+   Return a bytes object on success
+   Return NULL on failure
+*/
+static inline PyObject *
+_BlocksOutputBuffer_Finish(_BlocksOutputBuffer *buffer,
+                           const Py_ssize_t avail_out)
+{
+    PyObject *result, *block;
+    const Py_ssize_t list_len = Py_SIZE(buffer->list);
+
+    // fast path for single block
+    if ((list_len == 1 && avail_out == 0) ||
+        (list_len == 2 && Py_SIZE(PyList_GET_ITEM(buffer->list, 1)) == avail_out))
+    {
+        block = PyList_GET_ITEM(buffer->list, 0);
+        Py_INCREF(block);
+
+        Py_CLEAR(buffer->list);
+        return block;
+    }
+
+    // final bytes object
+    result = PyBytes_FromStringAndSize(NULL, buffer->allocated - avail_out);
+    if (result == NULL) {
+        PyErr_SetString(PyExc_MemoryError, unable_allocate_msg);
+        return NULL;
+    }
+
+    // memory copy
+    if (list_len > 0) {
+        char *posi = PyBytes_AS_STRING(result);
+
+        // blocks except the last one
+        Py_ssize_t i = 0;
+        for (; i < list_len-1; i++) {
+            block = PyList_GET_ITEM(buffer->list, i);
+            memcpy(posi, PyBytes_AS_STRING(block), Py_SIZE(block));
+            posi += Py_SIZE(block);
+        }
+        // the last block
+        block = PyList_GET_ITEM(buffer->list, i);
+        memcpy(posi, PyBytes_AS_STRING(block), Py_SIZE(block) - avail_out);
+    } else {
+        assert(Py_SIZE(result) == 0);
+    }
+
+    Py_CLEAR(buffer->list);
+    return result;
+}
+
+/* Clean up the buffer when an error occurred. */
+static inline void
+_BlocksOutputBuffer_OnError(_BlocksOutputBuffer *buffer)
+{
+    Py_CLEAR(buffer->list);
+}
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* Py_INTERNAL_BLOCKS_OUTPUT_BUFFER_H */

Lib/_compression.py

@@ -1,7 +1,7 @@
 """Internal classes used by the gzip, lzma and bz2 modules"""
 
 import io
-
+import sys
 
 BUFFER_SIZE = io.DEFAULT_BUFFER_SIZE  # Compressed data read chunk size
 
@@ -110,6 +110,16 @@ def read(self, size=-1):
         self._pos += len(data)
         return data
 
+    def readall(self):
+        chunks = []
+        # sys.maxsize means the max length of output buffer is unlimited,
+        # so that the whole input buffer can be decompressed within one
+        # .decompress() call.
+        while data := self.read(sys.maxsize):
+            chunks.append(data)
+
+        return b"".join(chunks)
+
     # Rewind the file to the beginning of the data stream.
     def _rewind(self):
         self._fp.seek(0)

Misc/NEWS.d/next/Library/2020-10-16-15-34-30.bpo-41486.Mu9Iit.rst

@@ -0,0 +1,4 @@
+Use a new output buffer management code for :mod:`bz2` / :mod:`lzma` /
+:mod:`zlib` modules, and add ``.readall()`` function to
+``_compression.DecompressReader`` class. These bring some performance
+improvements. Patch by Ma Lin.