Fixes issue #19929: Call os.read with 32768 within subprocess.Popen
communicate rather than 4096 for efficiency. A microbenchmark shows
Linux and OS X both using ~50% less cpu time this way.
diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 546a7a0..78e4fcf 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -1654,7 +1654,7 @@
if self._input_offset >= len(self._input):
close_unregister_and_remove(fd)
elif mode & select_POLLIN_POLLPRI:
- data = os.read(fd, 4096)
+ data = os.read(fd, 32768)
if not data:
close_unregister_and_remove(fd)
self._fd2output[fd].append(data)
diff --git a/Misc/NEWS b/Misc/NEWS
index 0eac7fb..5eacf9c 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -18,6 +18,10 @@
Library
-------
+- Issue #19929: Call os.read with 32768 within subprocess.Popen.communicate
+ rather than 4096 for efficiency. A microbenchmark shows Linux and OS X
+ both using ~50% less cpu time this way.
+
- Issue #19506: Use a memoryview to avoid a data copy when piping data
to stdin within subprocess.Popen.communicate. 5-10% less cpu usage.