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merge: mark file gets as not thread safe (issue5933)...
merge: mark file gets as not thread safe (issue5933) In default installs, this has the effect of disabling the thread-based worker on Windows when manifesting files in the working directory. My measurements have shown that with revlog-based repositories, Mercurial spends a lot of CPU time in revlog code resolving file data. This ends up incurring a lot of context switching across threads and slows down `hg update` operations when going from an empty working directory to the tip of the repo. On mozilla-unified (246,351 files) on an i7-6700K (4+4 CPUs): before: 487s wall after: 360s wall (equivalent to worker.enabled=false) cpus=2: 379s wall Even with only 2 threads, the thread pool is still slower. The introduction of the thread-based worker (02b36e860e0b) states that it resulted in a "~50%" speedup for `hg sparse --enable-profile` and `hg sparse --disable-profile`. This disagrees with my measurement above. I theorize a few reasons for this: 1) Removal of files from the working directory is I/O - not CPU - bound and should benefit from a thread pool (unless I/O is insanely fast and the GIL release is near instantaneous). So tests like `hg sparse --enable-profile` may exercise deletion throughput and aren't good benchmarks for worker tasks that are CPU heavy. 2) The patch was authored by someone at Facebook. The results were likely measured against a repository using remotefilelog. And I believe that revision retrieval during working directory updates with remotefilelog will often use a remote store, thus being I/O and not CPU bound. This probably resulted in an overstated performance gain. Since there appears to be a need to enable the thread-based worker with some stores, I've made the flagging of file gets as thread safe configurable. I've made it experimental because I don't want to formalize a boolean flag for this option and because this attribute is best captured against the store implementation. But we don't have a proper store API for this yet. I'd rather cross this bridge later. It is possible there are revlog-based repositories that do benefit from a thread-based worker. I didn't do very comprehensive testing. If there are, we may want to devise a more proper algorithm for whether to use the thread-based worker, including possibly config options to limit the number of threads to use. But until I see evidence that justifies complexity, simplicity wins. Differential Revision: https://phab.mercurial-scm.org/D3963

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hgignore.txt
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Synopsis
========
The Mercurial system uses a file called ``.hgignore`` in the root
directory of a repository to control its behavior when it searches
for files that it is not currently tracking.
Description
===========
The working directory of a Mercurial repository will often contain
files that should not be tracked by Mercurial. These include backup
files created by editors and build products created by compilers.
These files can be ignored by listing them in a ``.hgignore`` file in
the root of the working directory. The ``.hgignore`` file must be
created manually. It is typically put under version control, so that
the settings will propagate to other repositories with push and pull.
An untracked file is ignored if its path relative to the repository
root directory, or any prefix path of that path, is matched against
any pattern in ``.hgignore``.
For example, say we have an untracked file, ``file.c``, at
``a/b/file.c`` inside our repository. Mercurial will ignore ``file.c``
if any pattern in ``.hgignore`` matches ``a/b/file.c``, ``a/b`` or ``a``.
In addition, a Mercurial configuration file can reference a set of
per-user or global ignore files. See the ``ignore`` configuration
key on the ``[ui]`` section of :hg:`help config` for details of how to
configure these files.
To control Mercurial's handling of files that it manages, many
commands support the ``-I`` and ``-X`` options; see
:hg:`help <command>` and :hg:`help patterns` for details.
Files that are already tracked are not affected by .hgignore, even
if they appear in .hgignore. An untracked file X can be explicitly
added with :hg:`add X`, even if X would be excluded by a pattern
in .hgignore.
Syntax
======
An ignore file is a plain text file consisting of a list of patterns,
with one pattern per line. Empty lines are skipped. The ``#``
character is treated as a comment character, and the ``\`` character
is treated as an escape character.
Mercurial supports several pattern syntaxes. The default syntax used
is Python/Perl-style regular expressions.
To change the syntax used, use a line of the following form::
syntax: NAME
where ``NAME`` is one of the following:
``regexp``
Regular expression, Python/Perl syntax.
``glob``
Shell-style glob.
The chosen syntax stays in effect when parsing all patterns that
follow, until another syntax is selected.
Neither glob nor regexp patterns are rooted. A glob-syntax pattern of
the form ``*.c`` will match a file ending in ``.c`` in any directory,
and a regexp pattern of the form ``\.c$`` will do the same. To root a
regexp pattern, start it with ``^``.
Subdirectories can have their own .hgignore settings by adding
``subinclude:path/to/subdir/.hgignore`` to the root ``.hgignore``. See
:hg:`help patterns` for details on ``subinclude:`` and ``include:``.
.. note::
Patterns specified in other than ``.hgignore`` are always rooted.
Please see :hg:`help patterns` for details.
Example
=======
Here is an example ignore file. ::
# use glob syntax.
syntax: glob
*.elc
*.pyc
*~
# switch to regexp syntax.
syntax: regexp
^\.pc/