view tests/test-empty-group.t @ 39561:d06834e0f48e

wireprotov2peer: stream decoded responses

Previously, wire protocol version 2 would buffer all response data.
Only once all data was received did we CBOR decode it and resolve
the future associated with the command. This was obviously not
desirable. In future commits that introduce large response payloads,
this caused significant memory bloat and slowed down client
operations due to waiting on the server.

This commit refactors the response handling code so that response
data can be streamed.

Command response objects now contain a buffered CBOR decoder. As
new data arrives, it is fed into the decoder. Decoded objects are
made available to the generator as they are decoded.

Because there is a separate thread processing incoming frames and
feeding data into the response object, there is the potential for
race conditions when mutating response objects. So a lock has been
added to guard access to critical state variables.

Because the generator emitting decoded objects needs to wait on
those objects to become available, we've added an Event for the
generator to wait on so it doesn't busy loop. This does mean
there is the potential for deadlocks. And I'm pretty sure they can
occur in some scenarios. We already have a handful of TODOs around
this. But I've added some more. Fixing this will likely require
moving the background thread receiving frames into clienthandler.
We likely would have done this anyway when implementing the client
bits for the SSH transport.

Test output changes because the initial CBOR map holding the overall
response state is now always handled internally by the response
object.

Differential Revision: https://phab.mercurial-scm.org/D4474

#  A          B
#
#  3  4       3
#  |\/|       |\
#  |/\|       | \
#  1  2       1  2
#  \ /        \ /
#   0          0
#
# if the result of the merge of 1 and 2
# is the same in 3 and 4, no new manifest
# will be created and the manifest group
# will be empty during the pull
#
# (plus we test a failure where outgoing
# wrongly reported the number of csets)

  $ hg init a
  $ cd a
  $ touch init
  $ hg ci -A -m 0
  adding init
  $ touch x y
  $ hg ci -A -m 1
  adding x
  adding y

  $ hg update 0
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ touch x y
  $ hg ci -A -m 2
  adding x
  adding y
  created new head

  $ hg merge 1
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -A -m m1

  $ hg update -C 1
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge 2
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -A -m m2
  created new head

  $ cd ..

  $ hg clone -r 3 a b
  adding changesets
  adding manifests
  adding file changes
  added 4 changesets with 3 changes to 3 files
  new changesets 5fcb73622933:d15a0c284984
  updating to branch default
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg clone -r 4 a c
  adding changesets
  adding manifests
  adding file changes
  added 4 changesets with 3 changes to 3 files
  new changesets 5fcb73622933:1ec3c74fc0e0
  updating to branch default
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg -R a outgoing b
  comparing with b
  searching for changes
  changeset:   4:1ec3c74fc0e0
  tag:         tip
  parent:      1:79f9e10cd04e
  parent:      2:8e1bb01c1a24
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     m2
  
  $ hg -R a outgoing c
  comparing with c
  searching for changes
  changeset:   3:d15a0c284984
  parent:      2:8e1bb01c1a24
  parent:      1:79f9e10cd04e
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     m1
  
  $ hg -R b outgoing c
  comparing with c
  searching for changes
  changeset:   3:d15a0c284984
  tag:         tip
  parent:      2:8e1bb01c1a24
  parent:      1:79f9e10cd04e
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     m1
  
  $ hg -R c outgoing b
  comparing with b
  searching for changes
  changeset:   3:1ec3c74fc0e0
  tag:         tip
  parent:      1:79f9e10cd04e
  parent:      2:8e1bb01c1a24
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     m2
  

  $ hg -R b pull a
  pulling from a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 0 files (+1 heads)
  new changesets 1ec3c74fc0e0
  (run 'hg heads' to see heads, 'hg merge' to merge)

  $ hg -R c pull a
  pulling from a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 0 files (+1 heads)
  new changesets d15a0c284984
  (run 'hg heads' to see heads, 'hg merge' to merge)