RFR: 8245264: Test runtime/cds/appcds/SignedJar.java fails

[Yumin Qi]

Hi, Please review:

   bug: 8245264: Test runtime/cds/appcds/SignedJar.java fails
   Webrev: http://cr.openjdk.java.net/~minqi/2020/8245264/webrev-00/

Summary: When dump shared archive in safepoint, there may exist current 
work for StringTable or SymbolTable, which led to the table(s) not 
walkable. This led symbols not sorted and binary search for symbol 
(method in this case) failed in runtime. This problem might exist long 
time ago but not triggered until the change of jar signing code (bug 
8242151, https://bugs.openjdk.java.net/browse/JDK-8242151). 
<https://bugs.openjdk.java.net/browse/JDK-8242151>
    If table(s) work still in process, abort safepoint (exit from vm 
operation) to wait for them to finish then do dump work.

    (Thanks Ioi, Calvin, Coleen and David H ...  for help to identifying 
problem and suggest solution!)

    Tests: tier1, tier2.

    Thanks
    Yumin


<https://bugs.openjdk.java.net/browse/JDK-8242151>