Re: RFR(S): 8151259: [TESTBUG] nsk/jvmti/RedefineClasses/redefclass030 fails with "unexpected values of outer fields of the class" when running with -Xcomp

[Chris Plummer]

On 7/24/18 12:25 AM, serguei.spit...@oracle.com wrote: Hi Chris, I still feel, this fix adds more confusion and complexity. Let's look at some fragments. http://cr.openjdk.java.net/~cjplummer/8151259/webrev.00/test/hotspot/jtreg/vmTestbase/nsk/jvmti/RedefineClasses/redefclass028/redefclass028.c.frames.html 116 if ((strcmp(name, expHSMethod) == 0) && 117 (strcmp(sig, expHSSignature) == 0)) { 118 NSK_DISPLAY0("CompiledMethodLoad: a tested hotspot method found\n"); 119 120 // CR 6604375: check whether "hot" method was entered 121 if (enteredHotMethod) { 122 hsMethodID = method; 123 fire = 1; 124 } else { 125 NSK_DISPLAY0("Compilation occured before method execution\n"); 126 fire = 0; // Ignore this compilation. Wait for next one. 127 } 128 } I think, the line #126 is not needed. It just creates a confusion. The fire == 0 from beginning. Why do we need it to set to 0 again? Yes, it can be removed. I just didn't give it much thought when changing the code from -1 to 0. Is it because it can be already set to 1? Id so, I'm not sure I understand this code then. 187 } while(fire == 0); 188 189 NSK_DISPLAY0("agentProc: hotspot method compiled\n\n"); 190 192 if (fire == 1) { . . . 224 } else { 225 // fire == -1 226 // NOTE: This isn't suppose to happen anymore. Hot method should always end up being entered. 227 NSK_COMPLAIN0("agentProc: \"hot\" method wasn't executed. Don't perform redefinition\n"); 228 } I don't understand why do we need the check at the line #192. The variable fire can be only equal to 0 or 1. The only way out of the loop at the line #187 is if fire == 1. Then the else statement at the lines 224-228 confuses even more. The else section can be removed. I left it in as sort of an assert, but I see now that it just cause confusion. thanks, Chris On 7/23/18 20:19, Chris Plummer wrote: On 7/23/18 5:22 PM, serguei.spit...@oracle.com wrote: Hi Chris, On 7/23/18 11:40, Chris Plummer wrote: Hi Serguei, If the fix was complicated I would agree, but it really just boils down to this one line change: -            fire = -1; +            fire = 0; // Ignore this compilation. Wait for next one. It is not obvious that this will completely fix the problem. Is it possible that there will not be next compilation with the -Xcomp? It's only one method that we check for. I don't see why there would be 2nd -Xcomp compilation for it, but even if there was, the test will ignore it just like the first one. It will ignore compilations of the method until the flag has been set indicating the method has been executed once. If for some reason the method is never compiled after being executed once, the test will give up waiting for it (I think after 30 seconds) and produce an error. I'm afraid that it is what will always happen with the -Xcomp. Then there is no point to waist this by waiting for timeout as the test will successfully complete without testing anything. It seems to be not worth this complexity. I guess, you would want some extra tracing though. :) Thanks, Serguei If it is possible then it is better to explicitly exclude these tests for -Xcomp. Otherwise, consider this reviewed. Given that, I see no reason not to increase our test coverage by supporting this test during -Xcomp runs. I'd agree if it is going to be stable. If problems turn up in the future, we can reconsider disabling it. thanks, Chris Thanks, Serguei thanks, Chris On 7/23/18 9:44 AM, serguei.spit...@oracle.com wrote: Hi Chris, Would it be more simple to avoid running these tests with -Xcomp? I guess, this would work: @requires vm.compMode != "Xcomp" Thanks, Serguei On 7/23/18 00:42, Chris Plummer wrote: Hello, Please review the following fix for JDK11: https://bugs.openjdk.java.net/browse/JDK-8151259 http://cr.openjdk.java.net/~cjplummer/8151259/webrev.00 It fixes the following 3 tests: vmTestbase/nsk/jvmti/RedefineClasses/redefclass028.java vmTestbase/nsk/jvmti/RedefineClasses/redefclass029.java vmTestbase/nsk/jvmti/RedefineClasses/redefclass030.java Any of which could fail when run with -Xcomp with (followed by a bunch more errors):  # ERROR: Redefinition not started. Maybe running with -Xcomp. Test ignored. Although lately we've only seen this with redefclass030.java on macosx. These 3 tests do redefinition of a "hot" method after triggering compilation for it. After the redef some testing is done to ensure that the redef was done correctly, but the issue these test have actually comes before any redef is done. The test attempts to trigger compilation by calling a hot method a lot. The agent detects compilation by receiving a CompiledMethodLoad event. There was an issue discovered long ago that when -Xcomp is used, the compilation happens before the "hot" method is ever called. Then the redef would happen before compilation, and this somehow messed up the test (I'm not exactly sure how). The fix was to basically abandon the redef attempt when this problem is detected, and then supposedly just let the test run to completion (skipping the actual testing of the redef). After this change, if you ran with -Xcomp it would pass, but if you looked in the log you would see:  # ERROR: Redefinition not started. Maybe running with -Xcomp. Test ignored. However, there was a bug in the logic to make the test run to completion, and also causes the above message to not appear. Instead the test would fail with: # ERROR: Redefinition not completed. Followed by a bunch more error message during the part of the test that checks if the redef was done properly. If the CompiledMethodLoad event comes in before the hot method is ever called (which it does with -Xcomp), the test sets fire = -1. If the hot method was called, it is set to 1.  The setting of fire = -1 was added to fix the -Xcomp problem mentioned above. The jvmti agent does the following:     do {         THREAD_sleep(1);         /* wait for compilation to happen */     } while(fire == 0);     if (fire == 1) {         /* do the redef here */         NSK_DISPLAY0("agentProc: <<<<<<<< RedefineClasses() is successfully done\n");     } else {         // fire == -1         NSK_DISPLAY0("agentProc: \"hot\" method wasn't executed. Don't perform redefinition\n");     } The agent then syncs with the debuggee, waiting for it finish up. What the test expects is that waitForRedefinitionStarted() in the debuggee will time out after two seconds while waiting for fire == 1 (which it thinks will will always happen because it was set to -1). When it times out, the test does appear to exit properly with, but with the following in the log, which is intended:  # ERROR: Redefinition not started. Maybe running with -Xcomp. Test ignored. However, sometimes before waitForRedefinitionStarted() times out, the hot method is called enough times to trigger compilation. So another CompiledMethodLoad event arrives, and this time fire is set to 1. Because of this, waitForRedefinitionStarted() doesn't time out and returns with an indication that the redef has started. After this waitForRedefinitionCompleted() is executed. It waits for the redef to complete, but it never does since the agent decided not to do the redef when it saw fire == -1. So waitForRedefinitionCompleted() times out after 10 seconds and the test fails, with: # ERROR: Redefinition not completed. Actually the above error is not really what causes the failure. When the above error is detected, no error status is set and the test continues as if the redef had been done. So then the logic that detects if the redef was done properly ends up failing, and that's where the test actually indicates a failure status. You see a whole bunch of other errors in the log because of all the checks that fail. The fix is to not abandon the test when the first CompiledMethodLoad event is before the hot method was called. Instead just leave fire==0 and wait for the next CompiledMethodLoad event that is triggered after the method is called enough times to be recompiled. I'm not sure why it was not originally done this way. Possibly the recompilation did not happen reliably, but I have not run into this problem. The other changes in redefclass030.c are just cleaning up debug tracing. Another fix was to properly set the error status when waitForRedefinitionStarted() or waitForRedefinitionCompleted() times out, although this is just a safety net and I didn't run into any cases where this happened after fixing the CompiledMethodLoad event handling. So in general the changes in redefclass030.java were not needed, but provide better error handling. thanks, Chris