RFR (XS): JDK-8023145: G1: G1CollectedHeap::mark_strong_code_roots() needs to handle ParallelGCThreads=0

[Bengt Rutisson]

Thanks Stefan and Mikael for the reviews!

Bengt

On 8/16/13 11:23 AM, Mikael Gerdin wrote:
> Bengt,
>
> On 2013-08-16 10:35, Bengt Rutisson wrote:
>>
>> Hi everyone,
>>
>> Could I have a couple of reviews for this small change?
>> http://cr.openjdk.java.net/~brutisso/8023145/webrev.00/
>
> The fix looks good.
>
> /Mikael
>
>>
>>  From the bug report:
>>
>> With the fix for JDK-7145569 the method
>> G1CollectedHeap::mark_strong_code_roots() was introduced. However, this
>> method assumes that the work gang has been set up. If we are running
>> with ParallelGCThreads=0 we don't set up the work gang and thus get a
>> null pointer:
>>
>> This simple JTreg test illustrates the issue:
>>
>>
>> /**
>>   * @test Test8000311
>>   * @key gc
>>   * @bug 8000311
>>   * @summary G1: ParallelGCThreads==0 broken
>>   * @run main/othervm -XX:+UseG1GC -XX:ParallelGCThreads=0
>> -XX:+ResizePLAB -XX:+ExplicitGCInvokesConcurrent Test8000311
>>   * @author filipp.zhinkin at oracle.com
>>   */
>>
>> import java.util.*;
>>
>> public class Test8000311 {
>>    public static void main(String args[]) {
>>      for(int i = 0; i<100; i++) {
>>        byte[] garbage = new byte[1000];
>>        System.gc();
>>      }
>>    }
>> }
>>
>> It crashes with a null pointer:
>>
>> # SIGSEGV (0xb) at pc=0xffffffff7d3fadf4, pid=22622, tid=6
>>
>> si_addr=0x0000000000000000
>>
>> Native frames: (J=compiled Java code, j=interpreted, Vv=VM code,
>> C=native code)
>> V [libjvm.so+0x7fadf4] void
>> G1CollectedHeap::mark_strong_code_roots(unsigned)+0x44;;
>> __1cPG1CollectedHeapWmark_strong_code_roots6MI_v_+0x44
>> V [libjvm.so+0x7f5f80] void
>> G1CollectedHeap::g1_process_strong_roots(bool,SharedHeap::ScanningOption,OopClosure*,OopsInHeapRegionClosure*,G1KlassScanClosure*,int)+0x5e0;; 
>>
>> __1cPG1CollectedHeapXg1_process_strong_roots6MbnKSharedHeapOScanningOption_pnKOopClosure_pnXOopsInHeapRegionClosure_pnSG1KlassScanClosure_i_v_+0x5e0 
>>
>> V [libjvm.so+0x7fccdc] void G1ParTask::work(unsigned)+0x67c;;
>> __1cJG1ParTaskEwork6MI_v_+0x67c
>> V [libjvm.so+0x7f7500] void
>> G1CollectedHeap::evacuate_collection_set(EvacuationInfo&)+0x418;;
>> __1cPG1CollectedHeapXevacuate_collection_set6MrnOEvacuationInfo__v_+0x418 
>>
>> V [libjvm.so+0x7f1a84] bool
>> G1CollectedHeap::do_collection_pause_at_safepoint(double)+0x824;;
>> __1cPG1CollectedHeapbGdo_collection_pause_at_safepoint6Md_b_+0x824
>> V [libjvm.so+0x1241a7c] void VM_G1IncCollectionPause::doit()+0x2e4;;
>> __1cXVM_G1IncCollectionPauseEdoit6M_v_+0x2e4
>> V [libjvm.so+0x123de38] void VM_Operation::evaluate()+0xf8;;
>> __1cMVM_OperationIevaluate6M_v_+0xf8
>> V [libjvm.so+0x1239dcc] void
>> VMThread::evaluate_operation(VM_Operation*)+0x254;;
>> __1cIVMThreadSevaluate_operation6MpnMVM_Operation__v_+0x254
>> V [libjvm.so+0x123a83c] void VMThread::loop()+0x654;;
>> __1cIVMThreadEloop6M_v_+0x654
>> V [libjvm.so+0x1239834] void VMThread::run()+0xe4;;
>> __1cIVMThreadDrun6M_v_+0xe4
>> V [libjvm.so+0xef8af0] java_start+0x258;; java_start+0x258
>>
>> With the proposed fix the test passes.
>>
>> Thanks,
>> Bengt