RFR (S) 8130039: Move the platform-specific [OS]Semaphore code

[coleen.phillimore at oracle.com]

On 1/10/18 12:11 AM, David Holmes wrote:
> Hi Coleen,
>
> On 10/01/2018 3:17 AM, coleen.phillimore at oracle.com wrote:
>> On 1/9/18 8:14 AM, coleen.phillimore at oracle.com wrote:
>>>
>>>
>>> On 1/8/18 8:56 PM, David Holmes wrote:
>>>> Hi Coleen,
>>>>
>>>> Overall this seems okay but a few comments ...
>>>>
>>>> On 9/01/2018 8:34 AM, coleen.phillimore at oracle.com wrote:
>>>>> Also:
>>>>> 8130038: Unify the semaphore usage in os_xxx.cpp
>>>>>
>>>>> Tested with hs-tier1-5.  And 
>>>>> open/test/jdk/sun/misc/SunMiscSignalTest.java and closed signal 
>>>>> tests.
>>>>>
>>>>> open webrev at http://cr.openjdk.java.net/~coleenp/8130039.01/webrev
>>>>> bug link https://bugs.openjdk.java.net/browse/JDK-8130039
>>>>
>>>> With the removal of os::signal_lookup() the parameter to 
>>>> check_pending_signals becomes irrelevant and the "false" path 
>>>> becomes dead code. Not sure if it is worth deleting that.
>>>
>>> Yes, that's true.  I can delete it and the code for the "false" path.
>>>>
>>>> ---
>>>>
>>>> os_linux.cpp:
>>>>
>>>> static struct timespec create_timespec(unsigned int sec, int nsec) {
>>>>   struct timespec ts;
>>>>   // Semaphore's are always associated with CLOCK_REALTIME
>>>>   os::Linux::clock_gettime(CLOCK_REALTIME, &ts);
>>>>   // see unpackTime for discussion on overflow checking
>>>>
>>>> There's no longer a direct connection between create_timespec and 
>>>> the fact it is only used with semaphores - so the initial comment 
>>>> is no longer appropriate. But if you rename to 
>>>> create_semaphore_timespec then that restores the connection.
>>>>
>>>
>>> Ok, I'll rename it.
>>>
>>>> The final comment is not correct (my bad!) as unpackTime no longer 
>>>> exists since I factored out all the PlatformEvent code. It could say:
>>>>
>>>> // see os_posix.cpp for discussion on overflow checking
>>>
>>> I see, it's now similar to calc_rel_time in os_posix.cpp. I'll 
>>> change the comment as suggested in case calc_rel_time changes we 
>>> don't have to change this.
>>>>
>>>> but I'm wondering whether the timedwait API should be taking a 
>>>> timespec in the first place? If we pass secs and nsecs directly 
>>>> then we only need to convert to a timespec inside the low-level 
>>>> implementation that needs it ie in semaphore_posix.cpp. I don't 
>>>> recall if there was a reason we have to do the timespec conversion 
>>>> in a platform specific manner.
>>>>
>>>
>>> I didn't understand the difference between solaris and linux 
>>> create_timespec, so I left it in the platform specific code. The 
>>> solaris implementation *does* have unpackTime and the linux one does 
>>> not.  Or could I use the linux version in semaphore_posix.cpp ? That 
>>> would be better, but I wasn't sure if it was correct.   Let me know. 
>>> I'd like to make that change.
>>
>> No, looking again, the linux version of create_semaphore_timespec is 
>> competely different and I don't think I can unify these at this time.
>
> Well this is quite a mess :( The Solaris unpackTime code is 
> technically incorrect if Solaris is using posix semaphores because it 
> reads the time from gettimeofday, but the manpage for sem_timedwait 
> clearly states the timespec should be from CLOCK_REALTIME. So in 
> actuality what we currently have in the Linux code is what the shared 
> POSIX code should look like and what Solaris should actually use.
>
> Further, the non-OSX BSD code purports to use PosixSemaphore but it 
> defines:
>
> struct timespec PosixSemaphore::create_timespec(unsigned int sec, int 
> nsec) {
>   struct timespec ts;
>   unpackTime(&ts, false, (sec * NANOSECS_PER_SEC) + nsec);
>
>   return ts;
> }
>
> but there is no unpackTime method on BSD!

Right, there is no unpackTime on BSD so I removed this for BSD !APPLE 
semaphores, since nothing that we have compiles this, and anything that 
needs it has more work to do.

Yes, please file an RFE.  I might get to it but there was a complication 
for posix because it also needs to get this clock_gettime function:  
os::Linux::clock_gettime(CLOCK_REALTIME, &ts);  We're never done, but 
hopefully my change is a start.

Thanks,
Coleen
>
> I think we need a separate RFE to clean up this mess. I'll file one.
>
> Thanks,
> David
>
>> thanks,
>> Coleen
>>>> ---
>>>>
>>>> semaphore_posix.cpp
>>>>
>>>>   26 #ifndef __APPLE__
>>>>   27 #include "runtime/os.hpp"
>>>>   28 // POSIX unamed semaphores are not supported on OS X.
>>>>   29 #include "semaphore_posix.hpp"
>>>>   30 #include <semaphore.h>
>>>>   31 #endif
>>>>   32
>>>>   33
>>>>   34 // POSIX unamed semaphores are not supported on OS X.
>>>>   35 #ifndef __APPLE__
>>>>
>>>> The whole file contents should be ifndef __APPLE__ so this just 
>>>> reduces to:
>>>>
>>>>   // POSIX unamed semaphores are not supported on OS X.
>>>>   #ifndef __APPLE__
>>>>   #include "runtime/os.hpp"
>>>>   #include "semaphore_posix.hpp"
>>>>   #include <semaphore.h>
>>>>   ...
>>>>
>>>
>>> Ok.  I'll fix that.
>>>
>>> Thanks,
>>> Coleen
>>>> ---
>>>>
>>>> Thanks,
>>>> David
>>>>
>>>>> Thanks,
>>>>> Coleen
>>>
>>