[Python-checkins] cpython (3.3): Fixes issue #19506: Use a memoryview to avoid a data copy when piping data

[gregory.p.smith]

http://hg.python.org/cpython/rev/44948f5bdc12
changeset:   87819:44948f5bdc12
branch:      3.3
parent:      87813:78efa2c06447
user:        Gregory P. Smith <greg at krypto.org>
date:        Sat Dec 07 19:12:46 2013 -0800
summary:
  Fixes issue #19506: Use a memoryview to avoid a data copy when piping data
to stdin within subprocess.Popen.communicate.  5-10% less cpu usage.

files:
  Lib/subprocess.py |  7 +++++--
  Misc/NEWS         |  3 +++
  2 files changed, 8 insertions(+), 2 deletions(-)


diff --git a/Lib/subprocess.py b/Lib/subprocess.py
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -1621,6 +1621,9 @@
 
             self._save_input(input)
 
+            if self._input:
+                input_view = memoryview(self._input)
+
             while self._fd2file:
                 timeout = self._remaining_time(endtime)
                 if timeout is not None and timeout < 0:
@@ -1638,8 +1641,8 @@
 
                 for fd, mode in ready:
                     if mode & select.POLLOUT:
-                        chunk = self._input[self._input_offset :
-                                            self._input_offset + _PIPE_BUF]
+                        chunk = input_view[self._input_offset :
+                                           self._input_offset + _PIPE_BUF]
                         try:
                             self._input_offset += os.write(fd, chunk)
                         except OSError as e:
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -18,6 +18,9 @@
 Library
 -------
 
+- Issue #19506: Use a memoryview to avoid a data copy when piping data
+  to stdin within subprocess.Popen.communicate.  5-10% less cpu usage.
+
 - Issue #19839: Fix regression in bz2 module's handling of non-bzip2 data at
   EOF, and analogous bug in lzma module.
 

-- 
Repository URL: http://hg.python.org/cpython