view mercurial/help/revisions.txt @ 20208:61a47fd64f30 stable

fileset, revset: do not use global parser object for thread safety

parse() cannot be called at the same time because a parser object keeps its
states.  This is no problem for command-line hg client, but it would cause
strange errors in multi-threaded hgweb.

Creating parser object is not too expensive.

original:
% python -m timeit -s 'from mercurial import revset' 'revset.parse("0::tip")'
100000 loops, best of 3: 11.3 usec per loop

thread-safe:
% python -m timeit -s 'from mercurial import revset' 'revset.parse("0::tip")'
100000 loops, best of 3: 13.1 usec per loop

Mercurial supports several ways to specify individual revisions.

A plain integer is treated as a revision number. Negative integers are
treated as sequential offsets from the tip, with -1 denoting the tip,
-2 denoting the revision prior to the tip, and so forth.

A 40-digit hexadecimal string is treated as a unique revision
identifier.

A hexadecimal string less than 40 characters long is treated as a
unique revision identifier and is referred to as a short-form
identifier. A short-form identifier is only valid if it is the prefix
of exactly one full-length identifier.

Any other string is treated as a bookmark, tag, or branch name. A
bookmark is a movable pointer to a revision. A tag is a permanent name
associated with a revision. A branch name denotes the tipmost revision
of that branch. Bookmark, tag, and branch names must not contain the ":"
character.

The reserved name "tip" always identifies the most recent revision.

The reserved name "null" indicates the null revision. This is the
revision of an empty repository, and the parent of revision 0.

The reserved name "." indicates the working directory parent. If no
working directory is checked out, it is equivalent to null. If an
uncommitted merge is in progress, "." is the revision of the first
parent.