RFR: 8282469: Allow considered use of C++ thread_local in Hotspot

[Daniel D.Daugherty]

On Mon, 7 Mar 2022 21:21:28 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> src/hotspot/share/memory/operator_new.cpp line 37:
>> 
>>> 35: // a memory leak.  Use CHeapObj as the base class of such objects to make it explicit
>>> 36: // that they're allocated on the C heap.
>>> 37: // Commented out in product version to avoid conflicts with third-party C++ native code.
>> 
>> There's a little bit of policy information here that is being deleted.  It overlaps with the section `### Memory Allocation` in `hotspot-style.md`, but includes this information which might not be stated elsewhere:
>> 
>>> Typically, uses of the C++ global operator new are inadvertent and therefore often associated with memory leaks.
>> 
>> (This is my rephrasing, perhaps appropriate to the style guide.)
>> 
>> Or is a point like this made in the config file which prevents direct linkage?  (I don't know where that file is.)
>
> The link-time check is expressed in open/make/hotspot/lib/CompileJvm.gmk but simply states:
> 
> 
> # Hotspot disallows the use of global operators 'new' and 'delete'. This build
> # time check helps enforce this requirement. ...
> 
> 
> The prohibition on using global operator new should definitely be explicitly documented somewhere, so the style guide seems a suitable place.

I agree that the prohibition on using global operator new should definitely be explicitly documented somewhere and I'm good with adding that warning to the HotSpot style guide.

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PR: https://git.openjdk.java.net/jdk/pull/7719