userlocks.py

import os
import platform
import ctypes
import time
import datetime


class BaseUserLock(object):

    def __init__(self, filename):
        self.filename = filename
        self.locktime = None

    def __enter__(self):
        dirname = os.path.split(os.path.abspath(self.filename))[0]
        if not os.path.exists(dirname):
            os.makedirs(dirname)
        while True:
            if self.tryacquire(self.filename):
                break
            print("Lockfile " + self.filename + " not available.")
            print("Wait 30s...")
            time.sleep(30.0)
        self.locktime = datetime.datetime.now()
        print("Lock acquired at " + str(self.locktime))

    def __exit__(self, etype, einstance, etraceback):
        self.release()
        unlocktime = datetime.datetime.now()
        print("Lock released at " + str(unlocktime))
        print("Lock was held for " + str(unlocktime - self.locktime))


class WindowsUserLock(BaseUserLock):

    def __init__(self, name):
        BaseUserLock.__init__(self, os.environ["APPDATA"] + "\\openhome-build\\" + name + ".lock")

    def tryacquire(self, filename):
        self.handle = ctypes.windll.kernel32.CreateFileA(filename, 7, 0, 0, 2, 0x04000100, 0)
        return self.handle != -1

    def release(self):
        ctypes.windll.kernel32.CloseHandle(self.handle)


class PosixUserLock(BaseUserLock):

    def __init__(self, name):
        BaseUserLock.__init__(self, os.environ["HOME"] + "/.openhome-build/" + name + ".lock")

    def tryacquire(self, filename):
        import fcntl
        self.f = open(filename, "w")
        try:
            fcntl.lockf(self.f, fcntl.LOCK_EX)
            return True
        except IOError:
            self.f.close()
            return False

    def release(self):
        self.f.close()


def userlock(name):
    '''
    Acquire a lock scoped to the local user. Only one build at a time can run
    with the given name per user per machine. While waiting for the lock, prints
    a notice to stdout every 30s.
    '''
    if platform.system() == 'Windows':
        return WindowsUserLock(name)
    return PosixUserLock(name)