D757: dirstate: move opendirstatefile to dirstatemap

[foozy (Katsunori FUJIWARA)]

foozy added inline comments.

INLINE COMMENTS

> durham wrote in dirstate.py:1373-1374
> Agreed.  I'm not even sure what it's actually saying as a mercurial developer...

(sorry for late response)

With current implementation of dirstate, _pl() reads "dirstate"
file only for parents of wdir, and subsequent _read() will
read "dirstate" file again.

So, in this "changed parallelly" situation, 2 patterns are possible:

1. previous _pl() read 'dirstate.pending', but current _read() reads 'dirstate'
2. previous _pl() read 'dirstate', but current _read() reads 'dirstate.pending'

This should mean that:

- current (spawned) "hg" process is running parallelly from another "hg" process, which causes current transaction, and
- the latter process moves transaction processing forward without waiting for current "hg" process

For example:

1. committing (or aborting) transaction between _pl() and _read() removed 'dirstate.pending' file
2. changing "dirstate" in current (or next?) transaction newly creates 'dirstate.pending'

Spawning "hg" process from a hook process as background one can cause this.

Any hinting helps understanding ?

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D757

To: durham, #hg-reviewers, indygreg
Cc: foozy, indygreg, mercurial-devel