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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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patterns.txt
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Mercurial accepts several notations for identifying one or more files
at a time.
By default, Mercurial treats filenames as shell-style extended glob
patterns.
Alternate pattern notations must be specified explicitly.
.. note::
Patterns specified in ``.hgignore`` are not rooted.
Please see :hg:`help hgignore` for details.
To use a plain path name without any pattern matching, start it with
``path:``. These path names must completely match starting at the
current repository root, and when the path points to a directory, it is matched
recursively. To match all files in a directory non-recursively (not including
any files in subdirectories), ``rootfilesin:`` can be used, specifying an
absolute path (relative to the repository root).
To use an extended glob, start a name with ``glob:``. Globs are rooted
at the current directory; a glob such as ``*.c`` will only match files
in the current directory ending with ``.c``.
The supported glob syntax extensions are ``**`` to match any string
across path separators and ``{a,b}`` to mean "a or b".
To use a Perl/Python regular expression, start a name with ``re:``.
Regexp pattern matching is anchored at the root of the repository.
To read name patterns from a file, use ``listfile:`` or ``listfile0:``.
The latter expects null delimited patterns while the former expects line
feeds. Each string read from the file is itself treated as a file
pattern.
To read a set of patterns from a file, use ``include:`` or ``subinclude:``.
``include:`` will use all the patterns from the given file and treat them as if
they had been passed in manually. ``subinclude:`` will only apply the patterns
against files that are under the subinclude file's directory. See :hg:`help
hgignore` for details on the format of these files.
All patterns, except for ``glob:`` specified in command line (not for
``-I`` or ``-X`` options), can match also against directories: files
under matched directories are treated as matched.
For ``-I`` and ``-X`` options, ``glob:`` will match directories recursively.
Plain examples::
path:foo/bar a name bar in a directory named foo in the root
of the repository
path:path:name a file or directory named "path:name"
rootfilesin:foo/bar the files in a directory called foo/bar, but not any files
in its subdirectories and not a file bar in directory foo
Glob examples::
glob:*.c any name ending in ".c" in the current directory
*.c any name ending in ".c" in the current directory
**.c any name ending in ".c" in any subdirectory of the
current directory including itself.
foo/* any file in directory foo
foo/** any file in directory foo plus all its subdirectories,
recursively
foo/*.c any name ending in ".c" in the directory foo
foo/**.c any name ending in ".c" in any subdirectory of foo
including itself.
Regexp examples::
re:.*\.c$ any name ending in ".c", anywhere in the repository
File examples::
listfile:list.txt read list from list.txt with one file pattern per line
listfile0:list.txt read list from list.txt with null byte delimiters
See also :hg:`help filesets`.
Include examples::
include:path/to/mypatternfile reads patterns to be applied to all paths
subinclude:path/to/subignorefile reads patterns specifically for paths in the
subdirectory