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From "Gregory Shimansky (JIRA)" <j...@apache.org>
Subject [jira] Created: (HARMONY-4661) [drlvm][jvmti] MethodEntry and MethodExit event callbacks could be called only when needed
Date Tue, 21 Aug 2007 16:06:30 GMT
[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

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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