Acquire same VLAN in concurrency test

[rmotitsuki]

I was trying to force an Error to acquire Link VLANs and I ended acquiring the same VLAN number for multiple requests.
First I used a test_concurrently decorator to create a unit test.
I added a time.sleep(0.0001) between get_next_available_tag and use_tag to force a delay.

    def test_vlans(self):
        switch_a = Switch('00:00:00:00:00:01')
        switch_b = Switch('00:00:00:00:00:02')
        endpoint_a = Interface('eth0', 1, switch_a)
        endpoint_b = Interface('eth1', 2, switch_b)
        linkA = Link(endpoint_a, endpoint_b)

        @test_concurrently(10)
        def toggle_call_your_method_here():
            # perform the code you want to test here; it must be thread-safe
            vlan = linkA.get_next_available_tag()
            time.sleep(0.0001)
            linkA.use_tag(vlan)
            print('Link %s using %s vlan' % (linkA, vlan.value))

        toggle_call_your_method_here()

The result was:

Link <kytos.core.link.Link object at 0x7f9a3def3be0> using 1 vlan
Link <kytos.core.link.Link object at 0x7f9a3def3be0> using 2 vlan
Link <kytos.core.link.Link object at 0x7f9a3def3be0> using 3 vlan
Link <kytos.core.link.Link object at 0x7f9a3def3be0> using 4 vlan
Link <kytos.core.link.Link object at 0x7f9a3def3be0> using 4 vlan
Link <kytos.core.link.Link object at 0x7f9a3def3be0> using 5 vlan
Link <kytos.core.link.Link object at 0x7f9a3def3be0> using 5 vlan
Link <kytos.core.link.Link object at 0x7f9a3def3be0> using 6 vlan
Link <kytos.core.link.Link object at 0x7f9a3def3be0> using 5 vlan
Link <kytos.core.link.Link object at 0x7f9a3def3be0> using 6 vlan