The proposal is to encapsulate the nmethod mark for deoptimization logic in one
place and only allow access to the `mark_for_deoptimization` from a closure
object:
```C++
class DeoptimizationMarkerClosure : StackObj {
public:
virtual void marker_do(Deoptimization::MarkFn mark_fn) = 0;
};
This closure takes a `MarkFn` which it uses to mark which nmethods should be
deoptimized. This marking can only be done through the `MarkFn` and a `MarkFn`
can only be created in the following code which runs the closure.
```C++
{
NoSafepointVerifier nsv;
assert_locked_or_safepoint(Compile_lock);
marker_closure.marker_do(MarkFn());
anything_deoptimized = deoptimize_all_marked();
}
if (anything_deoptimized) {
run_deoptimize_closure();
}
This ensures that this logic is encapsulated and the `NoSafepointVerifier` and
`assert_locked_or_safepoint(Compile_lock)` makes `deoptimize_all_marked` not
having to scan the whole code cache sound.
The exception to this pattern, from `InstanceKlass::unload_class`, is discussed
in the JBS issue, and gives reasons why not marking for deoptimization there is
ok.
An effect of this encapsulation is that the deoptimization logic was moved from
the `CodeCache` class to the `Deoptimization` class and the class redefinition
logic was moved from the `CodeCache` class to the `VM_RedefineClasses`
class/operation.
Testing: Tier 1-5
-------------
Commit messages:
- JDK-8291237: Encapsulate nmethod Deoptimization logic
Changes: https://git.openjdk.org/jdk/pull/9655/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9655&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8291237
Stats: 719 lines in 21 files changed: 362 ins; 250 del; 107 mod
Patch: https://git.openjdk.org/jdk/pull/9655.diff
Fetch: git fetch https://git.openjdk.org/jdk pull/9655/head:pull/9655
PR: https://git.openjdk.org/jdk/pull/9655
