Avoid O(N**2) bottleneck in _communicate_(). Fixes #1598181. Backport from rev. 53295.
diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index eb1a735..8b25c2f 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -1111,6 +1111,7 @@
read_set.append(self.stderr)
stderr = []
+ input_offset = 0
while read_set or write_set:
rlist, wlist, xlist = select.select(read_set, write_set, [])
@@ -1118,9 +1119,9 @@
# When select has indicated that the file is writable,
# we can write up to PIPE_BUF bytes without risk
# blocking. POSIX defines PIPE_BUF >= 512
- bytes_written = os.write(self.stdin.fileno(), input[:512])
- input = input[bytes_written:]
- if not input:
+ bytes_written = os.write(self.stdin.fileno(), buffer(input, input_offset, 512))
+ input_offset += bytes_written
+ if input_offset >= len(input):
self.stdin.close()
write_set.remove(self.stdin)