mercurial/testing/__init__.py

util: make `mmapread()` work on Windows again

522b4d729e89 started referencing `mmap.MAP_PRIVATE`, but that's not available on
Windows, so `hg version` worked, but `make local` did not.  That commit also
started calling the constructor with the fine-grained `flags` and `prot` args,
but those aren't available on Windows either[1] (though the backing C code
doesn't seem conditionalized to disallow usage of them).

I assume the change away from from the `access` arg was to provide the same
options, plus `MAP_POPULATE`.  Looking at the source code[2], they're not quite
the same- `ACCESS_READ` is equivalent to `flags = MAP_SHARED` and `prot = PROT_READ`.
`MAP_PRIVATE` is only used with `ACCESS_COPY`, which allows read and write.
Therefore, we can't quite get the same baseline flags on Windows, but this was
the status quo ante and `MAP_POPULATE` is a Linux thing, so presumably it works.

I realize that typically the OS differences are abstracted into the platform
modules, but I'm leaving it here so that it is obvious what the differences are
between the platforms.

[1] https://docs.python.org/3/library/mmap.html#mmap.mmap
[2] https://github.com/python/cpython/blob/5e0abb47886bc665eefdcc19fde985f803e49d4c/Modules/mmapmodule.c#L1539

from __future__ import annotations

import os
import time


# work around check-code complains
#
# This is a simple log level module doing simple test related work, we can't
# import more things, and we do not need it.
environ = getattr(os, 'environ')


def wait_on_cfg(ui, cfg, timeout=10):
    """synchronize on the `cfg` config path

    Use this to synchronize commands during race tests.
    """
    full_config = b'sync.' + cfg
    wait_config = full_config + b'-timeout'
    sync_path = ui.config(b'devel', full_config)
    if sync_path is not None:
        timeout = ui.config(b'devel', wait_config)
        ready_path = sync_path + b'.waiting'
        write_file(ready_path)
        wait_file(sync_path, timeout=timeout)


def _timeout_factor():
    """return the current modification to timeout"""
    default = int(environ.get('HGTEST_TIMEOUT_DEFAULT', 360))
    current = int(environ.get('HGTEST_TIMEOUT', default))
    if current == 0:
        return 1
    return current / float(default)


def wait_file(path, timeout=10):
    timeout *= _timeout_factor()
    start = time.time()
    while not os.path.exists(path):
        if timeout and time.time() - start > timeout:
            raise RuntimeError(b"timed out waiting for file: %s" % path)
        time.sleep(0.01)


def write_file(path, content=b''):
    if content:
        write_path = b'%s.tmp' % path
    else:
        write_path = path
    with open(write_path, 'wb') as f:
        f.write(content)
    if path != write_path:
        os.rename(write_path, path)