comparison mercurial/util.py @ 29201:a109bf7e0dc2

util: make atomictempfile avoid ambiguity of file stat if needed

Ambiguity check is executed at close(), only if:

  - atomictempfile is created with checkambig=True, and
  - target file exists before renaming

This restriction avoids performance decrement by needless examination
of file stat (for example, filelog doesn't need exact cache
validation, even though it uses atomictempfile to write changes out).

See description of filestat class for detail about why the logic in
this patch works as expected.

This patch is a part of preparation for "Exact Cache Validation Plan":

    https://www.mercurial-scm.org/wiki/ExactCacheValidationPlan

29200:ca4065028e00

    close() when you are done writing, and atomictempfile will rename
    the temporary copy to the original name, making the changes
    visible. If the object is destroyed without being closed, all your
    writes are discarded.
    '''
    def __init__(self, name, mode='w+b', createmode=None):
        self.__name = name      # permanent name
        self._tempname = mktempcopy(name, emptyok=('w' in mode),
                                    createmode=createmode)
        self._fp = posixfile(self._tempname, mode)

        # delegated methods
        self.write = self._fp.write
        self.seek = self._fp.seek
        self.tell = self._fp.tell
        self.fileno = self._fp.fileno

    def close(self):
        if not self._fp.closed:
            self._fp.close()
            rename(self._tempname, localpath(self.__name))

    def discard(self):
        if not self._fp.closed:
            try:
                os.unlink(self._tempname)

29201:a109bf7e0dc2

    close() when you are done writing, and atomictempfile will rename
    the temporary copy to the original name, making the changes
    visible. If the object is destroyed without being closed, all your
    writes are discarded.
    '''
    def __init__(self, name, mode='w+b', createmode=None, checkambig=False):
        self.__name = name      # permanent name
        self._tempname = mktempcopy(name, emptyok=('w' in mode),
                                    createmode=createmode)
        self._fp = posixfile(self._tempname, mode)
        self._checkambig = checkambig

        # delegated methods
        self.write = self._fp.write
        self.seek = self._fp.seek
        self.tell = self._fp.tell
        self.fileno = self._fp.fileno

    def close(self):
        if not self._fp.closed:
            self._fp.close()
            filename = localpath(self.__name)
            oldstat = self._checkambig and filestat(filename)
            if oldstat and oldstat.stat:
                rename(self._tempname, filename)
                newstat = filestat(filename)
                if newstat.isambig(oldstat):
                    # stat of changed file is ambiguous to original one
                    advanced = (oldstat.stat.st_mtime + 1) & 0x7fffffff
                    os.utime(filename, (advanced, advanced))
            else:
                rename(self._tempname, filename)

    def discard(self):
        if not self._fp.closed:
            try:
                os.unlink(self._tempname)