tests/dumbhttp.py

hg: obtain lock when creating share from pooled repo (issue5104)

There are race conditions between clients performing a shared clone
to pooled storage:

1) Clients race to create the new shared repo in the pool directory
2) 1 client is seeding the repo in the pool directory and another goes
   to share it before it is fully cloned

We prevent these race conditions by obtaining a lock in the pool
directory that is derived from the name of the repo we will be
accessing.

To test this, a simple generic "lockdelay" extension has been added.
The extension inserts an optional, configurable delay before or after
lock acquisition. In the test, we delay 2 seconds after lock acquisition
in the first process and 1 second before lock acquisition in the 2nd
process. This means the first process has 1s to obtain the lock. There
is a race condition here. If we encounter it in the wild, we could
change the dummy extension to wait on the lock file to appear instead
of relying on timing. But that's more complicated. Let's see what
happens first.

#!/usr/bin/env python

from __future__ import absolute_import

"""
Small and dumb HTTP server for use in tests.
"""

import optparse
import BaseHTTPServer
import signal
import SimpleHTTPServer
import sys

from mercurial import (
    cmdutil,
)

OptionParser = optparse.OptionParser

class simplehttpservice(object):
    def __init__(self, host, port):
        self.address = (host, port)
    def init(self):
        self.httpd = BaseHTTPServer.HTTPServer(
            self.address, SimpleHTTPServer.SimpleHTTPRequestHandler)
    def run(self):
        self.httpd.serve_forever()

if __name__ == '__main__':
    parser = OptionParser()
    parser.add_option('-p', '--port', dest='port', type='int', default=8000,
        help='TCP port to listen on', metavar='PORT')
    parser.add_option('-H', '--host', dest='host', default='localhost',
        help='hostname or IP to listen on', metavar='HOST')
    parser.add_option('--pid', dest='pid',
        help='file name where the PID of the server is stored')
    parser.add_option('-f', '--foreground', dest='foreground',
        action='store_true',
        help='do not start the HTTP server in the background')
    parser.add_option('--daemon-pipefds')

    (options, args) = parser.parse_args()

    signal.signal(signal.SIGTERM, lambda x, y: sys.exit(0))

    if options.foreground and options.pid:
        parser.error("options --pid and --foreground are mutually exclusive")

    opts = {'pid_file': options.pid,
            'daemon': not options.foreground,
            'daemon_pipefds': options.daemon_pipefds}
    service = simplehttpservice(options.host, options.port)
    cmdutil.service(opts, initfn=service.init, runfn=service.run,
                    runargs=[sys.executable, __file__] + sys.argv[1:])