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
#require unix-permissions no-root no-windows
Prepare
$ hg init a
$ echo a > a/a
$ hg -R a ci -A -m a
adding a
$ hg clone a b
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
Test that raising an exception in the release function doesn't cause the lock to choke
$ cat > testlock.py << EOF
> from mercurial import error, registrar
>
> cmdtable = {}
> command = registrar.command(cmdtable)
>
> def acquiretestlock(repo, releaseexc):
> def unlock():
> if releaseexc:
> raise error.Abort(b'expected release exception')
> l = repo._lock(repo.vfs, b'testlock', False, unlock, None, b'test lock')
> return l
>
> @command(b'testlockexc')
> def testlockexc(ui, repo):
> testlock = acquiretestlock(repo, True)
> try:
> testlock.release()
> finally:
> try:
> testlock = acquiretestlock(repo, False)
> except error.LockHeld:
> raise error.Abort(b'lockfile on disk even after releasing!')
> testlock.release()
> EOF
$ cat >> $HGRCPATH << EOF
> [extensions]
> testlock=$TESTTMP/testlock.py
> EOF
$ hg -R b testlockexc
abort: expected release exception
[255]
One process waiting for another
$ cat > hooks.py << EOF
> import time
> def sleepone(**x): time.sleep(1)
> def sleephalf(**x): time.sleep(0.5)
> EOF
$ echo b > b/b
$ hg -R b ci -A -m b --config hooks.precommit="python:`pwd`/hooks.py:sleepone" > stdout &
$ hg -R b up -q --config ui.timeout.warn=0 --config hooks.pre-update="python:`pwd`/hooks.py:sleephalf" \
> > preup-stdout 2>preup-stderr
$ wait
$ cat preup-stdout
$ cat preup-stderr
waiting for lock on working directory of b held by process '*' on host '*' (glob)
got lock after * seconds (glob)
$ cat stdout
adding b
On processs waiting on another, warning after a long time.
$ echo b > b/c
$ hg -R b ci -A -m b --config hooks.precommit="python:`pwd`/hooks.py:sleepone" > stdout &
$ hg -R b up -q --config hooks.pre-update="python:`pwd`/hooks.py:sleephalf" \
> --config ui.timeout.warn=250 \
> > preup-stdout 2>preup-stderr
$ wait
$ cat preup-stdout
$ cat preup-stderr
$ cat stdout
adding c
On processs waiting on another, warning disabled.
$ echo b > b/d
$ hg -R b ci -A -m b --config hooks.precommit="python:`pwd`/hooks.py:sleepone" > stdout &
$ hg -R b up -q --config hooks.pre-update="python:`pwd`/hooks.py:sleephalf" \
> --config ui.timeout.warn=-1 \
> > preup-stdout 2>preup-stderr
$ wait
$ cat preup-stdout
$ cat preup-stderr
$ cat stdout
adding d
check we still print debug output
On processs waiting on another, warning after a long time (debug output on)
$ echo b > b/e
$ hg -R b ci -A -m b --config hooks.precommit="python:`pwd`/hooks.py:sleepone" > stdout &
$ hg -R b up --config hooks.pre-update="python:`pwd`/hooks.py:sleephalf" \
> --config ui.timeout.warn=250 --debug\
> > preup-stdout 2>preup-stderr
$ wait
$ cat preup-stdout
calling hook pre-update: hghook_pre-update.sleephalf
waiting for lock on working directory of b held by process '*' on host '*' (glob)
got lock after * seconds (glob)
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cat preup-stderr
$ cat stdout
adding e
On processs waiting on another, warning disabled, (debug output on)
$ echo b > b/f
$ hg -R b ci -A -m b --config hooks.precommit="python:`pwd`/hooks.py:sleepone" > stdout &
$ hg -R b up --config hooks.pre-update="python:`pwd`/hooks.py:sleephalf" \
> --config ui.timeout.warn=-1 --debug\
> > preup-stdout 2>preup-stderr
$ wait
$ cat preup-stdout
calling hook pre-update: hghook_pre-update.sleephalf
waiting for lock on working directory of b held by process '*' on host '*' (glob)
got lock after * seconds (glob)
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cat preup-stderr
$ cat stdout
adding f
Pushing to a local read-only repo that can't be locked
$ chmod 100 a/.hg/store
$ hg -R b push a
pushing to a
searching for changes
abort: could not lock repository a: Permission denied
[20]
$ chmod 700 a/.hg/store