[jira] Updated: (HARMONY-4661) [drlvm][jvmti] MethodEntry and MethodExit event callbacks could be called only when needed

["Gregory Shimansky (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HARMONY-4661?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Gregory Shimansky updated HARMONY-4661:
---------------------------------------

    Attachment: HARMONY-4661.patch

Here is the patch from the VM side that sets and clears method entry/exit flags on request from the agent(s).

> [drlvm][jvmti] MethodEntry and MethodExit event callbacks could be called only when needed
> ------------------------------------------------------------------------------------------
>
>                 Key: HARMONY-4661
>                 URL: https://issues.apache.org/jira/browse/HARMONY-4661
>             Project: Harmony
>          Issue Type: Improvement
>          Components: DRLVM
>            Reporter: Gregory Shimansky
>            Assignee: Gregory Shimansky
>         Attachments: HARMONY-4661.patch
>
>
> Currently when JIT compiles a method with flags exe_notify_method_entry or exe_notify_method_exit it hardcodes a call to VM helper at the beginning or end of method. This VM helper tries to determine whether there is some JVMTI environment that is subscribed to receiving such event at the moment. When there is no such environment nothing is done and the call to VM helper is not needed.
> We could create global flags for MethodEntry and MethodExit events that would be checked in JITted code whether or not it is necessary to call VM helper, so that it would be called only when a flag is set. This would eliminate redundant calls to VM from JITted code when no JVMTI environment is registered to receiving an event and speed up debugging.
> I suggest adding the following methods to VM interface
> void get_method_entry_flag_address(char **flag_address);
> void get_method_exit_flag_address(char **flag_address);
> which JIT would call when a method is compiled with exe_notify_method_entry or exe_notify_method_exit flags, and hardcode a check for the flag inside of the method before calling VM helper.
> VM would set these flags when some environment calls jvmtiSetEventNotificationMode enabling MethodEntry or MethodExit events and clear these flags when events are disabled.

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