(10) (M) RFR: 8174231: Factor out and share PlatformEvent and Parker code for POSIX systems

[David Holmes]

On 19/05/2017 7:25 PM, Robbin Ehn wrote:
> On 05/19/2017 11:07 AM, David Holmes wrote:
>>
>> They have to be as there are three cases:
>>
>> 1. Relative wait using CLOCK_MONOTONIC
>> 2. Relative wait using gettimeofday()
>> 3. Absolute wait using gettimeofday()
>>
>>> Please consider something like:
>>>
>>> #ifdef SUPPORTS_CLOCK_MONOTONIC
>>>    if (_use_clock_monotonic_condattr  && !isAbsolute) { // Why aren't 
>>> we using this when not isAbsolute is set?
>>>                                 // I suggest removing that check from 
>>> this if and use monotonic for that also.
>>
>> Absolute waits have to be based on wall-clock time and follow any 
>> adjustments made to wall clock time. In contrast relative waits should 
>> never be affected by wall-clock time adjustments hence the use of 
>> CLOCK_MONOTONIC when available.
>>
>> In Java the relative timed-waits are:
>> - Thread.sleep(ms)
>> - Object.wait(ms)/wait(ms,ns)
>> - LockSupport.parkNanos(ns) (and all the j.u.c blocking methods built 
>> on top of it)
>>
>> While the only absolute timed-wait we have is the 
>> LockSupport.parkUntil method(s).
>>
>> Hope that clarifies things.
> 
> Yes thanks!
> 
> But you can still re-factoring to something similar to what I suggested 
> and two of the calculation should be the same just ns vs us, correct?

There are three different forms of the calculation. The two relative 
time versions use a different time function and so a different time 
structure (timeval vs timespec) and a different calculation.

> Leaving the if statement with the "!isAbsolute" check, in my head 
> calc_time is something like:
> 
> void calc_time(...) {
>    if (isAbsolute) {
>      calc_abs_time(...);
>    } else {
#ifdef SUPPORTS_CLOCK_MONOTONIC
>      calc_rel_time_from_clock_monotonic(...);
#else
 >      calc_rel_time_from_gettimeofday(...);
#endif
>    }
> }

David
-----

> I do not see a problem with this, only better readability?
> 
> /Robbin
> 
>>
>> Thanks,
>> David
>> -----
>>
>>>       struct timespec now;
>>>       int status = _clock_gettime(CLOCK_MONOTONIC, &now);
>>>       assert_status(status == 0, status, "clock_gettime");
>>>       calc_time(abstime, timeout, isAbsolute, now.tv_sec, 
>>> now.tv_nsec, NANOUNITS);
>>>    } else {
>>> #else
>>>    {
>>> #endif
>>>       struct timeval now;
>>>       int status = gettimeofday(&now, NULL);
>>>       assert(status == 0, "gettimeofday");
>>>       calc_time(abstime, timeout, isAbsolute, now.tv_sec, 
>>> now.tv_usec, MICROUNITS);
>>>    }
>>> #endif
>>>
>>> Thanks for fixing this!
>>>
>>> /Robbin