8262328: Templatize JVMFlag boilerplate access methods

[iklam]

We have a bunch of boilerplate method like:

JVMFlagAccess::boolAtPut (JVMFlag* f, bool* v, JVMFlagOrigin origin)
JVMFlagAccess::intAtPut (JVMFlag* f, int* v, JVMFlagOrigin origin)
JVMFlagAccess::uintAtPut (JVMFlag* f, uint* v, JVMFlagOrigin origin)
...

Similarly, we also have 8 different functions: JVMFlag::{set_bool, set_int, set_intx, ...}

We should replace such patterns with

template <typename T>
JVMFlagAccess::set(JVMFlag* f, T* value, JVMFlagOrigin origin)

This would allow us to templatize the 8x boilerplate functions in writeableFlags.cpp.

The flag access code in whitebox.cpp can also be improved.

---

Progress

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Issue

• JDK-8262328: Templatize JVMFlag boilerplate access methods

Reviewers

• David Holmes (@dholmes-ora - Reviewer) ⚠️ Review applies to 4c0c8ae
• Gerard Ziemski (@gerard-ziemski - Committer) ⚠️ Review applies to 4c0c8ae

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Webrevs

• 03: Full (e3280b69)
• 02: Full - Incremental (4c0c8ae2)
• 01: Full - Incremental (58160ff0)
• 00: Full (86ce3ce7)

[iklam]

I need to work on this PR some more. Closing it for now.

[iklam]

I've updated the patch and the JVMFlagAccess API should have identical behavior as before. Now it's ready to be reviewed again.

[dholmes-ora]

Hi Ioi,

In terms of readability and writeability I prefer <type>AtPut() over set<JVM_FLAG_TYPE(type)>(). Is there any way to push the JVM_FLAG_TYPE down a level so it doesn't shout at you when reading the code? set<type>() would look much much better.

Thanks,
David

[iklam]

Hi Ioi,

In terms of readability and writeability I prefer AtPut() over set<JVM_FLAG_TYPE(type)>(). Is there any way to push the JVM_FLAG_TYPE down a level so it doesn't shout at you when reading the code? set() would look much much better.

Thanks,
David

I added the JVMFlagAccess::set_<type>() functions back (they are the same as the old <type>AtPut functions, but with a more consistent naming style).

Now I use the more low-level set<JVM_FLAG_TYPE(type)>() only in templates where the type is not statically known. E.g, WriteableFlags::set_flag_impl().

---

A related note: in an earlier version, I tried to get rid of the <JVM_FLAG_TYPE(type)> altogether, where the code is much cleaner with template type inference.

JVMFlag* flag = someSizetFlag;
size_t s = 0;
JVMFlagAccess::set(flag, &s, origin);

However, this may allow type mismatch like the following, on platforms that use the exact same type for size_t and uint:

JVMFlag* flag = someSizetFlag;
uint s = 0;
JVMFlagAccess::set(flag, &s, origin);

but you will get a runtime failure on platforms where size_t is not the same as uint. So I decided against this design due to non-portability.

[dholmes-ora]

Hi Ioi,

This latest version looks good to me.

Thanks,
David

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@iklam This change now passes all automated pre-integration checks.

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8262328: Templatize JVMFlag boilerplate access methods

Reviewed-by: dholmes, gziemski

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[gerard-ziemski]

I'm taking a look at your fix Ioi. Building it locally, wanted to check out a few things...

[gerard-ziemski]

Very nice! With all this reduction and "templatization" effort, soon we will be left with one line of a template code at this rate :-)

The only feedback I have is that I wish we could replace int type_enum with FlagType type_enum

[iklam]

Very nice! With all this reduction and "templatization" effort, soon we will be left with one line of a template code at this rate :-)

The only feedback I have is that I wish we could replace int type_enum with FlagType type_enum

Hi Gerard, thanks for the review. Replacing the int with enum will cause quite a bit of changes, so I would probably do that in a separate RFE.

[iklam]

Thanks @dholmes-ora and @gerard-ziemski for the review!
/integrate

[openjdk]

@iklam Pushed as commit 627ad9f.

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