RFR(M) 8212605: Pure-Java implementation of AccessController.doPrivileged

[dean.long at oracle.com]

Thanks Mandy.  I also appreciate you noticing (off-list) that I can 
remove the extra space in "Class <?>" in several places.  I have updated 
webrev.4 in place.

dl

On 11/2/18 1:55 PM, Mandy Chung wrote:
> Hi Dean,
>
> I reviewed webrev.4 version.  It looks good.  Happy to see moving the 
> doPrivileged support to Java and the performance improvement.
>
> On 10/31/18 3:23 PM, dean.long at oracle.com wrote:
>> https://bugs.openjdk.java.net/browse/JDK-8212605
>> http://cr.openjdk.java.net/~dlong/8212605/webrev.1
>>
>> This change implements AccessController.doPrivileged in Java. This 
>> gives a performance improvement while also being useful to Project 
>> Loom by removing the Java --> native --> Java transition.  One reason 
>> doPrivileged has historically been in native is because of the need 
>> to guarantee the cleanup of the privileged context when doPrivileged 
>> returns.  To do that in Java, the information that 
>> AccessController.getContext needs is pushed onto the Java stack as 
>> arguments to a method that getContext will recognize during its stack 
>> walk.  This allows us to remove the native privileged stack while 
>> guaranteeing that the privileged context goes away when the method 
>> returns.
>> Tested with tier1-tier3 hotspot and jdk tests and JCK 
>> api/java_security tests.  For the first few rounds of testing, I kept 
>> the old native privileged stack and compared the results of the old 
>> and new implementations for each getContext call, which did catch 
>> some early bugs.  The changes were also examined by internal security 
>> experts and run through additional internal security tests.
>>
>> The improvement on this [1] doPrivileged microbenchmark is 
>> approximate 50x.
>>
>> There is no attempt to optimize getContext() or security permission 
>> checks in this change, however, this is intended to be a first step 
>> towards other possible improvements, for example those proposed here 
>> [2].
>>
>
> FYI.  Sean and I also did some experiment to replace 
> JVM_GetStackAccessControlContext with StackWalker some time ago. 
> Another potential area to move the code from VM to Java for the future 
> as David explored and probably involves  performance work in the stack 
> walker.
>
> Mandy