RFR: 8074101: Add verification that all tasks are actually claimed during roots processing [v2]

[Albert Mingkun Yang]

On Tue, 12 Jan 2021 17:14:10 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> src/hotspot/share/gc/g1/g1RootProcessor.cpp line 66:
>> 
>>> 64:   // already processed in java roots.
>>> 65:   _process_strong_tasks.try_claim_task(G1RP_PS_CodeCache_oops_do);
>>> 66: #endif
>> 
>> Rather than these fake claims, consider something like this:
>> 
>> template<typename... Ts>
>> void all_tasks_completed(uint nworkers, Ts... tags) {
>>   // Type-check more_skipped are all of the same type as first_skipped.
>>   T0 typed_skipped[] = { first_skipped, more_skipped... };
>>   uint skipped[] = { static_cast<uint>(tags)... };
>>   all_tasks_completed_impl(nworkers, skipped, ARRAY_SIZE(skipped));
>> }
>> 
>> void all_tasks_completed(uint nworkers) {
>>   all_tasks_completed_impl(nworkers, nullptr, 0);
>> }
>> 
>> Usage:
>> 
>> all_tasks_completed(n_workers(),
>>                     G1RP_PS_CodeCache_oops_do,
>>                     G1RP_PS_refProcessor_oops_do)
>> 
>> all_tasks_completed_impl can check that all tasks have been claimed except
>> the skipped ones, which have not been claimed.
>> 
>> There might be better ways to write the variadic all_tasks_completed.  It's
>> been a while since I've done anything with variadic templates.
>
> Here's a better version of the variadic `all_tasks_completed`
> 
> template<typename T0, typename... Ts,
>          ENABLE_IF(Conjunction<std::is_same<T0, Ts>...>::value)>
> void all_tasks_completed(uint n_threads, T0 first_skipped, Ts... more_skipped) {
>   static_assert(std::is_convertible<T0, uint>::value, "not convertible");
>   uint skipped[] = { static_cast<uint>(first_skipped), static_cast<uint>(more_skipped)... };
>   all_tasks_completed_impl(n_threads, skipped, ARRAY_SIZE(skipped));
> }
> `Conjunction` is in metaprogramming/logical.hpp.

Thank you; updated as suggested.

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PR: https://git.openjdk.java.net/jdk/pull/2046