bundle2: fail faster when interrupted Before this patch, bundle2 application attempted to consume remaining bundle2 part data when the process is interrupted (SIGINT) or when sys.exit is called (translated into a SystemExit exception). This meant that if one of these occurred when applying a say 1 GB changegroup bundle2 part being downloaded over a network, it may take Mercurial *several minutes* to terminate after a SIGINT because the process is waiting on the network to stream megabytes of data. This is not a great user experience and a regression from bundle1. Furthermore, many process supervisors tend to only give processes a finite amount of time to exit after delivering SIGINT: if processes take too long to self-terminate, a SIGKILL is issued and Mercurial has no opportunity to clean up. This would mean orphaned locks and transactions. Not good. This patch changes the bundle2 application behavior to fail faster when an interrupt or system exit is requested. It does so by not catching BaseException (which includes KeyboardInterrupt and SystemExit) and by explicitly checking for these conditions in yet another handler which would also seek to the end of the current bundle2 part on failure. The end result of this patch is that SIGINT is now reacted to significantly faster: the active transaction is rolled back immediately without waiting for incoming bundle2 data to be consumed. This restores the pre-bundle2 behavior and makes Mercurial treat signals with the urgency they deserve.

--- a/mercurial/bundle2.py	Sun Aug 07 14:58:49 2016 +0900
+++ b/mercurial/bundle2.py	Thu Aug 25 19:53:14 2016 -0700
@@ -353,7 +353,7 @@
     try:
         for nbpart, part in iterparts:
             _processpart(op, part)
-    except BaseException as exc:
+    except Exception as exc:
         for nbpart, part in iterparts:
             # consume the bundle content
             part.seek(0, 2)
@@ -382,6 +382,7 @@
     The part is guaranteed to have been fully consumed when the function exits
     (even if an exception is raised)."""
     status = 'unknown' # used by debug output
+    hardabort = False
     try:
         try:
             handler = parthandlermapping.get(part.type)
@@ -436,9 +437,15 @@
                 outpart = op.reply.newpart('output', data=output,
                                            mandatory=False)
                 outpart.addparam('in-reply-to', str(part.id), mandatory=False)
+    # If exiting or interrupted, do not attempt to seek the stream in the
+    # finally block below. This makes abort faster.
+    except (SystemExit, KeyboardInterrupt):
+        hardabort = True
+        raise
     finally:
         # consume the part content to not corrupt the stream.
-        part.seek(0, 2)
+        if not hardabort:
+            part.seek(0, 2)
 
 
 def decodecaps(blob):