view README @ 32334:6e0d1043e8fc

fsmonitor: acquire localrepo.wlock prior to emitting hg.update state

we see some weird things in the watchman logs where the mercurial
process is seemingly confused about which hg.update state it is publishing
through watchman.

On closer examination, we're seeing conflicting pids for the clients involved
and this implies a race.

To resolve this, we extend the wlock around the state-enter/state-leave
events that are emitted to watchman.

Test Plan:
Some manual testing:

In one window, run this, and then checkout a different rev:

```
$ watchman -p -j <<<'["subscribe", "/data/users/wez/fbsource", "wez", {"expression": ["name", ".hg/updatestate"]}]'
{
    "version": "4.9.0",
    "subscribe": "wez",
    "clock": "c:1495034090:814028:1:312576"
}
{
    "state-enter": "hg.update",
    "version": "4.9.0",
    "clock": "c:1495034090:814028:1:312596",
    "unilateral": true,
    "subscription": "wez",
    "metadata": {
        "status": "ok",
        "distance": 125,
        "rev": "a1275d79ffa6c58b53116c8ec401c275ca6c1e2a",
        "partial": false
    },
    "root": "/data/users/wez/fbsource"
}
{
    "root": "/data/users/wez/fbsource",
    "metadata": {
        "status": "ok",
        "distance": 125,
        "rev": "a1275d79ffa6c58b53116c8ec401c275ca6c1e2a",
        "partial": false
    },
    "subscription": "wez",
    "unilateral": true,
    "version": "4.9.0",
    "clock": "c:1495034090:814028:1:312627",
    "state-leave": "hg.update"
}
```

Tailed the watchman log file and looked for invalid state assertion errors,
then ran my `rebase-all` script to update/rebase all of my heads.

Didn't trigger the error condition (but couldn't reliably trigger it previously
anyway), and the output captured above shows that the states are being emitted
correctly.

Mercurial
=========

Mercurial is a fast, easy to use, distributed revision control tool
for software developers.

Basic install:

 $ make            # see install targets
 $ make install    # do a system-wide install
 $ hg debuginstall # sanity-check setup
 $ hg              # see help

Running without installing:

 $ make local      # build for inplace usage
 $ ./hg --version  # should show the latest version

See https://mercurial-scm.org/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.