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https://github.com/python/cpython/commit/8fa124868519eeda0a6dfe9191ceabd708d84fa7
commit: 8fa124868519eeda0a6dfe9191ceabd708d84fa7
branch: main
author: morotti <r.morotti@gmail.com>
committer: serhiy-storchaka <storchaka@gmail.com>
date: 2024-04-23T18:51:20+03:00
summary:

gh-117151: optimize BufferedWriter(), do not buffer writes that are the buffer size (GH-118037)

BufferedWriter() was buffering calls that are the exact same size as the buffer. it's a very common case to read/write in blocks of the exact buffer size.

it's pointless to copy a full buffer, it's costing extra memory copy and the full buffer will have to be written in the next call anyway.

Co-authored-by: rmorotti <romain.morotti@man.com>

files:
M Modules/_io/bufferedio.c

diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
index 4133d3438253dd..aa52711941d374 100644
--- a/Modules/_io/bufferedio.c
+++ b/Modules/_io/bufferedio.c
@@ -2092,7 +2092,7 @@ _io_BufferedWriter_write_impl(buffered *self, Py_buffer *buffer)
self->raw_pos = 0;
}
avail = Py_SAFE_DOWNCAST(self->buffer_size - self->pos, Py_off_t, Py_ssize_t);
- if (buffer->len <= avail) {
+ if (buffer->len <= avail && buffer->len < self->buffer_size) {
memcpy(self->buffer + self->pos, buffer->buf, buffer->len);
if (!VALID_WRITE_BUFFER(self) || self->write_pos > self->pos) {
self->write_pos = self->pos;
@@ -2161,7 +2161,7 @@ _io_BufferedWriter_write_impl(buffered *self, Py_buffer *buffer)
/* Then write buf itself. At this point the buffer has been emptied. */
remaining = buffer->len;
written = 0;
- while (remaining > self->buffer_size) {
+ while (remaining >= self->buffer_size) {
Py_ssize_t n = _bufferedwriter_raw_write(
self, (char *) buffer->buf + written, buffer->len - written);
if (n == -1) {

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