Merge pull request #300 from Pylons/fix-265

stabilize buffer behavior with multiple requests on the same connection

2 files changed, 24 insertions, 3 deletions

diff --git a/CHANGES.txt b/CHANGES.txt
index 701c2b0..c40246b 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,3 +1,14 @@
+Unreleased
+----------
+
+- Fix an issue with keep-alive connections in which memory usage was higher
+  than expected because output buffers were being reused across requests on
+  a long-lived connection and each buffer would not be freed until it was full
+  or the connection was closed. Buffers are now rotated per-request to
+  stabilize their behavior.
+
+  See https://github.com/Pylons/waitress/pull/300
+
 1.4.3 (2020-02-02)
 ------------------
 
diff --git a/src/waitress/channel.py b/src/waitress/channel.py
index a8bc76f..bc9a2bb 100644
--- a/src/waitress/channel.py
+++ b/src/waitress/channel.py
@@ -174,9 +174,10 @@ class HTTPChannel(wasyncore.dispatcher, object):
                     # there's no current task, so we don't need to try to
                     # lock the outbuf to append to it.
                     outbuf_payload = b"HTTP/1.1 100 Continue\r\n\r\n"
+                    num_bytes = len(outbuf_payload)
                     self.outbufs[-1].append(outbuf_payload)
-                    self.current_outbuf_count += len(outbuf_payload)
-                    self.total_outbufs_len += len(outbuf_payload)
+                    self.current_outbuf_count += num_bytes
+                    self.total_outbufs_len += num_bytes
                     self.sent_continue = True
                     self._flush_some()
                     request.completed = False
@@ -311,7 +312,7 @@ class HTTPChannel(wasyncore.dispatcher, object):
                     self.outbufs.append(nextbuf)
                     self.current_outbuf_count = 0
                 else:
-                    if self.current_outbuf_count > self.adj.outbuf_high_watermark:
+                    if self.current_outbuf_count >= self.adj.outbuf_high_watermark:
                         # rotate to a new buffer if the current buffer has hit
                         # the watermark to avoid it growing unbounded
                         nextbuf = OverflowableBuffer(self.adj.outbuf_overflow)
@@ -399,6 +400,15 @@ class HTTPChannel(wasyncore.dispatcher, object):
                     # at the end to account for consecutive service() calls
                     if len(self.requests) > 1:
                         self._flush_outbufs_below_high_watermark()
+
+                    # this is a little hacky but basically it's forcing the
+                    # next request to create a new outbuf to avoid sharing
+                    # outbufs across requests which can cause outbufs to
+                    # not be deallocated regularly when a connection is open
+                    # for a long time
+                    if self.current_outbuf_count > 0:
+                        self.current_outbuf_count = self.adj.outbuf_high_watermark
+
                     request = self.requests.pop(0)
                     request.close()