RFR (S) JDK-8008962: NPG: Memory regression: One extra Monitor per ConstantPool

[Ioi Lam]

Please review:
http://cr.openjdk.java.net/~iklam/8008962/constpool_lock_001/ 
<http://cr.openjdk.java.net/%7Eiklam/8008962/constpool_lock_001/>

Bug: 8008962: NPG: Memory regression: One extra Monitor per ConstantPool
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8008962
https://jbs.oracle.com/bugs/browse/JDK-8008962 (Oracle Internal)

Summary of fix:

     The fix is implemented according to Coleen's suggestion in the 
bug's comments.

     Instead of using a Monitor for each ConstantPool (~150 bytes per 
class), I
     re-use InstanceKlass::init_lock() for locking the ConstantPool.

     init_lock used to be cleared after the class had been initialized. 
There was
     complicated code that needed to deal with the clearing (using volatile,
     OrderAccess::storestore(), etc). This code is no longer necessary 
and has been
     removed.

     The overhead is reduced to one int[0] per class.

     Because the lock is used at two different levels (class 
initialization, and
     ConstantPool access), I thought about the possibility of deadlocks. 
However,
     it seems the only case of a deadlock would be some sort of circular 
dependency
     in running <clinit> (as in the following example). However, in this 
case, a
     deadlock would have already happened, just from grabbing the 
initialization
     locks, before we would even have a chance to access the 
ConstantPools. Hence,
     reusing the lock for ConstantPool access doesn't add any new paths 
for deadlocks.

     -------------------------------
     public class ConcurClinit {
         static void sleep(int ms) {
             try {Thread.sleep(ms);} catch (Throwable t) {;}
         }
         static class A {
             static {
                 sleep(1000);
                 B.xxx();
                 sleep(1000);
             }
             static void xxx() {}
         }
         static class B {
             static {
                 sleep(1000);
                 A.xxx();
                 sleep(1000);
             }
             static void xxx() {}
         }
         public static void main(String args[]) {
             (new Thread() {
                     public void run() {
                         A a = new A();
                     }
                 }).start();
             (new Thread() {
                     public void run() {
                         B b = new B();
                     }
                 }).start();
         }
     }
     -------------------------------

Tests executed:

     * JPRT
     * JCK (vm, lang, api/signaturetest)
     * UTE (vm.runtime.testlist, vm.quick.testlist, 
vm.parallel_class_loading.testlist
)

Thanks,
Ioi
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