[PATCH] Work around performance bug in subprocess.Popen.communicate()

From: Karl Wiberg <kha@virtutech.com>
Date: Jul 31, 2009, 09:36 UTC
Message-ID: <20090731093632.7018.24435.stgit@october.e.vtech>

From: Karl Wiberg <kha@treskal.com>

In Python 2.4 (specifically, I tested with 2.4.6 on Ubuntu 9.04), subprocess.Popen.communicate() seems to take time proportional to the square of the size of the indata, which makes it ridiculously expensive to write stack log entries when the diffs are large. Work around the bug by calling subprocess.Popen.stdin.write() manually instead of letting communicate() handle the indata.

The performance bug has been fixed in Python 2.6 (I tested with 2.6.2), so with that version this workaround doesn't affect the run time. I haven't tested with Python 2.5.

This fixes bug 13319.

Signed-off-by: Karl Wiberg <kha@treskal.com>

---

 stgit/run.py |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/stgit/run.py b/stgit/run.py
index 7493ed3..311d12f 100644
--- a/stgit/run.py
+++ b/stgit/run.py
@@ -110,7 +110,9 @@ class Run:
                                  stdin = subprocess.PIPE,
                                  stdout = subprocess.PIPE,
                                  stderr = subprocess.PIPE)
-            outdata, errdata = p.communicate(self.__indata)
+            if self.__indata:
+                p.stdin.write(self.__indata)
+            outdata, errdata = p.communicate()
             self.exitcode = p.returncode
         except OSError, e:
             raise self.exc('%s failed: %s' % (self.__cmd[0], e))