JDK-8336325 : Add back UseHeavyMonitors as a develop option
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: runtime
  • Priority: P4
  • Status: Open
  • Resolution: Unresolved
  • Submitted: 2024-07-12
  • Updated: 2025-04-22
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JDK 26
26Unresolved
Related Reports
Relates :  
JDK-8334299 - Deprecate LockingMode option, along with LM_LEGACY and LM_MONITOR
Relates :  
JDK-8344261 - Obsolete the LockingMode flag and related code
Description
Add back UseHeavyMonitors as a develop option if wanted to replace LockingMode=LM_MONITOR.  Also fix platform dependent code:

static bool useHeavyMonitors() {
#if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
  return LockingMode == LM_MONITOR;
#else
  return false;
#endif
}

Why is ARM excluded?
Comments
When we remove LockingMode == LM_LEGACY, we should remove LockingMode=LM_MONITOR also. UseHeavyMonitors shouldn't be added back but we could add a develop option to go slow path from the assembly code instead, which was the original intent of UseHeavyMonitors. It was for debugging which is a lot easier from C++ code than macroAssembler.
11-03-2025