dirstate-tree: Avoid BTreeMap double-lookup when inserting a dirstate entry
The child nodes of a given node in the tree-shaped dirstate are kept in a
`BTreeMap` where keys are file names as strings. Finding or inserting a value
in the map takes `O(log(n))` string comparisons, which adds up when constructing
the tree.
The `entry` API allows finding a "spot" in the map that may or may not be
occupied and then access that value or insert a new one without doing map
lookup again. However the current API is limited in that calling `entry`
requires an owned key (and so a memory allocation), even if it ends up not
being used in the case where the map already has a value with an equal key.
This is still a win, with 4% better end-to-end time for `hg status` measured
here with hyperfine:
```
Benchmark #1: ../hg2/hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1
Time (mean ± σ): 1.337 s ± 0.018 s [User: 892.9 ms, System: 437.5 ms]
Range (min … max): 1.316 s … 1.373 s 10 runs
Benchmark #2: ./hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1
Time (mean ± σ): 1.291 s ± 0.008 s [User: 853.4 ms, System: 431.1 ms]
Range (min … max): 1.283 s … 1.309 s 10 runs
Summary
'./hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1' ran
1.04 ± 0.02 times faster than '../hg2/hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1'
```
* ./hg is this revision
* ../hg2/hg is its parent
* $REPO is an old snapshot of mozilla-central
Differential Revision: https://phab.mercurial-scm.org/D10550
test children command
$ cat <<EOF >> $HGRCPATH
> [extensions]
> children =
> EOF
init
$ hg init t
$ cd t
no working directory
$ hg children
setup
$ echo 0 > file0
$ hg ci -qAm 0 -d '0 0'
$ echo 1 > file1
$ hg ci -qAm 1 -d '1 0'
$ echo 2 >> file0
$ hg ci -qAm 2 -d '2 0'
$ hg co null
0 files updated, 0 files merged, 2 files removed, 0 files unresolved
$ echo 3 > file3
$ hg ci -qAm 3 -d '3 0'
hg children at revision 3 (tip)
$ hg children
$ hg co null
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
hg children at nullrev (should be 0 and 3)
$ hg children
changeset: 0:4df8521a7374
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: 0
changeset: 3:e2962852269d
tag: tip
parent: -1:000000000000
user: test
date: Thu Jan 01 00:00:03 1970 +0000
summary: 3
$ hg co 1
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
hg children at revision 1 (should be 2)
$ hg children
changeset: 2:8f5eea5023c2
user: test
date: Thu Jan 01 00:00:02 1970 +0000
summary: 2
$ hg co 2
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
hg children at revision 2 (other head)
$ hg children
$ for i in null 0 1 2 3 '2^'; do
> echo "hg children -r '$i'"
> hg children -r $i
> done
hg children -r 'null'
changeset: 0:4df8521a7374
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: 0
changeset: 3:e2962852269d
tag: tip
parent: -1:000000000000
user: test
date: Thu Jan 01 00:00:03 1970 +0000
summary: 3
hg children -r '0'
changeset: 1:708c093edef0
user: test
date: Thu Jan 01 00:00:01 1970 +0000
summary: 1
hg children -r '1'
changeset: 2:8f5eea5023c2
user: test
date: Thu Jan 01 00:00:02 1970 +0000
summary: 2
hg children -r '2'
hg children -r '3'
hg children -r '2^'
changeset: 2:8f5eea5023c2
user: test
date: Thu Jan 01 00:00:02 1970 +0000
summary: 2
hg children -r 0 file0 (should be 2)
$ hg children -r 0 file0
changeset: 2:8f5eea5023c2
user: test
date: Thu Jan 01 00:00:02 1970 +0000
summary: 2
hg children -r 1 file0 (should be 2)
$ hg children -r 1 file0
changeset: 2:8f5eea5023c2
user: test
date: Thu Jan 01 00:00:02 1970 +0000
summary: 2
$ hg co 0
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
hg children file0 at revision 0 (should be 2)
$ hg children file0
changeset: 2:8f5eea5023c2
user: test
date: Thu Jan 01 00:00:02 1970 +0000
summary: 2
should be compatible with templater (don't pass fctx to displayer)
$ hg children file0 -Tdefault
changeset: 2:8f5eea5023c2
user: test
date: Thu Jan 01 00:00:02 1970 +0000
summary: 2
$ cd ..