RFR(XS): 8215009: GCC 8 compilation eror in libjli

Dmitry Chuyko dmitry.chuyko at bell-sw.com
Mon Feb 25 17:09:50 UTC 2019 

On 2/22/19 9:55 PM, Roger Riggs wrote:
> Hi,
>
> After a closer look, I'd take the route of the 01 webrev.
> It is more localized and does not force the function signature needed
> by pthread_create to be propagated elsewhere.
>
> The code can be a lot more comprehensible by renaming the CallIntFunc
> function to be specific to ContinueInNewThread0. It looks like a 
> trampoline to me.
> The data structure being passed is on the stack of the caller of 
> pthread_create.
> It seems safe to refer to it here because the caller will wait in 
> pthread_join.

After some hesitation it looks like ContinueInNewThread0 may know about 
JavaMain just like ContinueInNewThread, no need to work with abstract 
continuation. Even that abstract continuation is limited to int return 
type. In webrev.02 continuation gets platform specific signature. But 
then we have to cast the result where the call is direct. Another 
approach in that direction could be to add result field in JavaMainArgs, 
but it will again force ContinueInNewThread0 to know about 
continuation's parameters structure as there may be a direct call of 
continuation.

If we let ContinueInNewThread0 call only JavaMain, it all can work 
without extra trampoline structures (just need a wrapper):

http://cr.openjdk.java.net/~dchuyko/8215009/webrev.03/

-Dmitry

>
> Also important is to document that the return type is specific to the OS
> and is needed to cast the return value expected by the 
> start_pthread_create
> start_routine.  That may still be in question because pthread_create
> expects void*.
>
> $.02, Roger
>
>
> On 02/22/2019 10:32 AM, Roger Riggs wrote:
>> Hi,
>>
>> If the warning can be addressed with an extra in-line cast then that's
>> cleaner and easier to understand than replicating that structure in 3 
>> files.
>> And of course, add a comment.
>> To make the source more readable, the cast could be factored
>> into a macro in the same file with the comment about why it is needed.
>>
>> Roger
>>
>>
>> On 02/21/2019 11:07 PM, David Holmes wrote:
>>> On 22/02/2019 4:55 am, Mikael Vidstedt wrote:
>>>>
>>>> The wrapper based solution looks much cleaner to me as well. 
>>>> webrev.01 looks good.
>>>
>>> Sorry I really don't like it. The wrappers obfuscate and make 
>>> complicated something that is not at all complicated. I have to 
>>> re-read the new code 3 times to figure out what it is even doing!
>>>
>>> All that complexity to handle the fact one platform wants to return 
>>> int instead of void* ??
> The complexity is due to the function being called in some other thread
> context and there is a necessary cast/type conversion on the return value
> from the start_routine that has to come back through pthread to 
> pthread_join.
>
>
>>>
>>> David
>>> -----
>>>
>>>> (not a Reviewer)
>>>>
>>>> Cheers,
>>>> Mikael
>>>>
>>>>> On Feb 21, 2019, at 9:55 AM, Dmitry Chuyko 
>>>>> <dmitry.chuyko at bell-sw.com> wrote:
>>>>>
>>>>> To me thread function wrappers look preferable to platform 
>>>>> specific JavaMain signature. Consider this webrev with wrappers:
>>>>>
>>>>> http://cr.openjdk.java.net/~dchuyko/8215009/webrev.01/
>>>>>
>>>>> In some cases JavaMain is called in the same thread and its result 
>>>>> is returned from JLI_Launch. ContinueInNewThread is in shared 
>>>>> code. And JavaMain uses macro controlled returns.
>>>>> So when JavaMain returns THREAD_FUNC_RETURN changes may contain 
>>>>> some quite artificial macro parts in java.c:
>>>>>
>>>>> http://cr.openjdk.java.net/~dchuyko/8215009/webrev.02/
>>>>>
>>>>> -Dmitry
>>>>>
>>>>> On 12/19/18 9:27 AM, David Holmes wrote:
>>>>>> On 19/12/2018 1:56 am, Dmitry Chuyko wrote:
>>>>>>> On 12/18/18 3:39 AM, David Holmes wrote:
>>>>>>>> On 11/12/2018 9:30 pm, Dmitry Chuyko wrote:
>>>>>>>>> On 12/11/18 4:03 AM, David Holmes wrote:
>>>>>>>>>> Hi Dmitry,
>>>>>>>>>>
>>>>>>>>>> On 11/12/2018 12:16 am, Dmitry Chuyko wrote:
>>>>>>>>>>> Hello,
>>>>>>>>>>>
>>>>>>>>>>> Please review a small fix in java_md_solinux.c: continuation 
>>>>>>>>>>> is not truly compatible with pthread_create start_routine's 
>>>>>>>>>>> signature but we control what actually happens. So it makes 
>>>>>>>>>>> sense to add intermediate void* cast to silence the error.
>>>>>>>>>>
>>>>>>>>>> I'd be tempted to fix the signature and get rid of all the 
>>>>>>>>>> casts.
>>>>>>>>>
>>>>>>>>> David, the signature is a signature of
>>>>>>>>>
>>>>>>>>> int JNICALL JavaMain(void * _args)
>>>>>>>>>
>>>>>>>>> It would be fun to change it. But still on Windows it is 
>>>>>>>>> correctly passed to _beginthreadex() and then return code is 
>>>>>>>>> extracted with GetExitCodeThread(). In case we want it to 
>>>>>>>>> return void* the cast will move there.
>>>>>>>>
>>>>>>>> I think the current double cast is truly ugly and an ifdef for 
>>>>>>>> windows, or a cast for Windows only would be an improvement.
>>>>>>>
>>>>>>> I agree. Maybe making a wrapper function is not so ugly. If 
>>>>>>> there are no objections to changing beginning of the call stack 
>>>>>>> it is quite easy to implement. For consistency it may be done 
>>>>>>> for all 3 points (posix unix, posix mac, windows) or just for 
>>>>>>> posix ones.
>>>>>>>
>>>>>>> It looks like ifdef should be better as long as there are 
>>>>>>> already OS-specific parts in libjli. Again, if there are no 
>>>>>>> objections to have different JavaMain signatures on different 
>>>>>>> platforms. In this case there won't be a signature cast for 
>>>>>>> Windows.
>>>>>>
>>>>>> How about setting
>>>>>>
>>>>>> #define THREAD_FUNC_RETURN int
>>>>>>
>>>>>> in windows/java_md.h.
>>>>>>
>>>>>> Then:
>>>>>>
>>>>>> #ifndef THREAD_FUNC_RETURN
>>>>>>    #define THREAD_FUNC_RETURN void*
>>>>>> #endif
>>>>>>
>>>>>> in java.h (after the other includes).
>>>>>>
>>>>>> Then:
>>>>>>
>>>>>> THREAD_FUNC_RETURN JNICALL
>>>>>> JavaMain(void * _args)
>>>>>>
>>>>>> in java.c.
>>>>>>
>>>>>> ?
>>>>>>
>>>>>> Cheers,
>>>>>> David
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> -Dmitry
>>>>>>>
>>>>>>>>
>>>>>>>> But I won't impose that on you just to silence gcc 8.
>>>>>>>>
>>>>>>>> Cheers,
>>>>>>>> David
>>>>>>>>
>>>>>>>>> -Dmitry
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Cheers,
>>>>>>>>>> David
>>>>>>>>>>
>>>>>>>>>>> bug: https://bugs.openjdk.java.net/browse/JDK-8215009
>>>>>>>>>>> webrev: http://cr.openjdk.java.net/~dchuyko/8215009/webrev.00/
>>>>>>>>>>> testing: submit repo 
>>>>>>>>>>> (mach5-one-dchuyko-JDK-8215009-20181207-1625-13615: PASSED)
>>>>>>>>>>>
>>>>>>>>>>> -Dmitry
>>>>>>>>>>>
>>>>
>>
>

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