RFR: 8359437: Make users and test suite not able to set LockingMode flag

[Anton Artemov]

On Wed, 18 Jun 2025 18:23:58 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> This PR contains changes for the 1st phase of the `LockingMode` flag obsoletion. 
>> 
>> The work is done by @fbredber, I have taken it over and am finishing it while he's on vacation. 
>> 
>> In the 1st phase one keeps the `LockingMode` variable in all places, but makes it non-settable from the command line. All the C1 and C2 code related to legacy locking will still be in place (but as dead code) and removed later (phase 2).
>> 
>> Lightweight locking is the default locking from now on.
>> 
>> Tested in tiers 1 - 7.
>
> test/hotspot/jtreg/runtime/Monitor/TestRecursiveLocking.java line 125:
> 
>> 123: public class TestRecursiveLocking {
>> 124:     static final WhiteBox WB = WhiteBox.getWhiteBox();
>> 125:     static final boolean flagHeavyMonitors = WB.getBooleanVMFlag("VerifyHeavyMonitors");
> 
> I think you should take out the VerifyHeavyMonitors cases.  @fbredber originally had that flag turn on a the reintroduced UseHeavyMonitors option but the UseHeavyMonitors option doesn't actually do that with this change.  I don't think this test will pass with -XX:+VerifyHeavyMonitors.
> If we reintroduce UseHeavyMonitors, save this diff and fix this test then.  Right now it's not correct.

Removed in the latest commit.

> test/hotspot/jtreg/runtime/lockStack/TestLockStackCapacity.java line 42:
> 
>> 40: public class TestLockStackCapacity {
>> 41:     static final WhiteBox WB = WhiteBox.getWhiteBox();
>> 42:     static final boolean flagHeavyMonitors = WB.getBooleanVMFlag("VerifyHeavyMonitors");
> 
> I think this should also not have cases for VerifyHeavyMonitors. We can add back tests if we want UseHeavyMonitors.  As of now, removing the Legacy locking code will remove code that reaches the VerifyHeavyMonitors branches.

Removed in the latest commit.

> test/jtreg-ext/requires/VMProps.java line 424:
> 
>> 422:      * Note: Lightweight locking does not support RTM (for now).
>> 423:      */
>> 424:     protected String vmRTMCompiler() {
> 
> There's an issue to remove this function since it's now unused.

Removed in the latest commit.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25847#discussion_r2161282585
PR Review Comment: https://git.openjdk.org/jdk/pull/25847#discussion_r2161282345
PR Review Comment: https://git.openjdk.org/jdk/pull/25847#discussion_r2161282101