[ovs-dev] [PATCH v3] timeval: Use monotonic time in OVS Python timeval library.

[Ryan Wilson 76511]

Hey Yamamoto,

Sorry for the delay, I finally set up my NetBSD environment and tested
this script. You're right, but NetBSD will actually return an error on
clock_gettime because of this argument difference. Thus, NetBSD will
continue to use time.time(), which is as expected.

I can add NetBSD functionality such that clock_gettime with
CLOCK_MONOTONIC can also be used for NetBSD as well. Lemme know!

Ryan

On 5/31/14 11:14 PM, "YAMAMOTO Takashi" <yamamoto at valinux.co.jp> wrote:

>> Python's time.time() function uses the system wall clock. However,
>> if NTP resets the wall clock to be a time in the past, then this
>> causes any applications that poll block based on time, such as
>> ovs-xapi-sync, to poll block indefinitely since the time is
>> unexpectedly negative.
>> 
>> This patch fixes the issue by using time.monotonic() if Python's
>> version >= 3.3. Otherwise, the timeval module calls out to the
>> librt C shared library and uses the clock_gettime function with
>> CLOCK_MONOTONIC.
>> 
>> Note this is only enabled on Linux-based platforms. This has been
>> tested on Ubuntu 12.04 and Redhat 6.4.
>> 
>> Bug #1189434
>> Signed-off-by: Ryan Wilson <wryan at nicira.com>
>> 
>> ---
>> v2: Pre-load librt.so.1 library instead of loading at every function
>> call. Use only CLOCK_MONOTONIC for consistency with OVS C library.
>> v3: Edit commit message, remove if-linux check
>> ---
>>  python/ovs/timeval.py |   34 +++++++++++++++++++++++++++++++++-
>>  1 file changed, 33 insertions(+), 1 deletion(-)
>> 
>> diff --git a/python/ovs/timeval.py b/python/ovs/timeval.py
>> index ba0e54e..f2681ac 100644
>> --- a/python/ovs/timeval.py
>> +++ b/python/ovs/timeval.py
>> @@ -12,13 +12,45 @@
>>  # See the License for the specific language governing permissions and
>>  # limitations under the License.
>>  
>> +import ctypes
>> +import sys
>>  import time
>>  
>> +LIBRT = 'librt.so.1'
>> +CLOCK_MONOTONIC = 1
>> +
>> +class timespec(ctypes.Structure):
>> +    _fields_ = [
>> +        ('tv_sec', ctypes.c_long),
>
>on NetBSD, timespec.tv_sec is int64_t, not long.
>
>YAMAMOTO Takashi
>
>> +        ('tv_nsec', ctypes.c_long),
>> +    ]
>> +
>> +try:
>> +    librt = ctypes.CDLL(LIBRT)
>> +    clock_gettime = librt.clock_gettime
>> +    clock_gettime.argtypes = [ctypes.c_int, ctypes.POINTER(timespec)]
>> +except:
>> +    # Librt shared library could not be loaded
>> +    librt = None
>> +
>> +def monotonic():
>> +    if not librt:
>> +        return time.time()
>> +
>> +    t = timespec()
>> +    if clock_gettime(CLOCK_MONOTONIC, ctypes.pointer(t)) == 0:
>> +        return t.tv_sec + t.tv_nsec * 1e-9
>> +    # Kernel does not support CLOCK_MONOTONIC
>> +    return time.time()
>> +
>> +# Use time.monotonic() if Python version >= 3.3
>> +if not hasattr(time, 'monotonic'):
>> +    time.monotonic = monotonic
>>  
>>  def msec():
>>      """Returns the current time, as the amount of time since the
>>epoch, in
>>      milliseconds, as a float."""
>> -    return time.time() * 1000.0
>> +    return time.monotonic() * 1000.0
>>  
>>  
>>  def postfork():
>> -- 
>> 1.7.9.5