
"""
Utilities for the OpenFlow test framework
"""

import random
import time
import os

default_timeout = None # set by oft

def gen_xid():
    return random.randrange(1,0xffffffff)

"""
Wait on a condition variable until the given function returns non-None or a timeout expires.
The condition variable must already be acquired.
The timeout value -1 means use the default timeout.
There is deliberately no support for an infinite timeout.
TODO: get the default timeout from configuration
"""
def timed_wait(cv, fn, timeout=-1):
    if timeout == -1:
        # TODO make this configurable
        timeout = default_timeout

    end_time = time.time() + timeout
    while True:
        val = fn()
        if val != None:
            return val

        remaining_time = end_time - time.time()
        cv.wait(remaining_time)

        if time.time() > end_time:
            return None

class EventDescriptor():
    """
    Similar to a condition variable, but can be passed to select().
    Only supports one waiter.
    """

    def __init__(self):
        self.pipe_rd, self.pipe_wr = os.pipe()

    def __del__(self):
        os.close(self.pipe_rd)
        os.close(self.pipe_wr)

    def notify(self):
        os.write(self.pipe_wr, "x")

    def wait(self):
        os.read(self.pipe_rd, 1)

    def fileno(self):
        return self.pipe_rd