RFR (XS) 8230415 : Avoid redundant permission checking in FilePermissionCollection and SocketPermissionCollection

[Ivan Gerasimov]

Hello!

In the two implementations of PermissionCollection.implies(Permission), 
all the permissions are traversed, and their corresponding bit mask are 
checked.

For example, here's a snippet from FilePermission.java:

         int desired = fperm.getMask();
         int effective = 0;
         int needed = desired;

         for (Permission perm : perms.values()) {
             FilePermission fp = (FilePermission)perm;
             if (((needed & fp.getMask()) != 0) && 
fp.impliesIgnoreMask(fperm)) {
                 effective |= fp.getMask();
                 if ((effective & desired) == desired) {
                     return true;
                 }
                 needed = (desired ^ effective);// <<< should be 
(desired & ~effective)
             }
         }

Here, if a permission's mask `fp.getMask()` intersects with `needed`, 
but does not fully cover all the needed bits, the variable `needed` is 
updated as XOR of desired and effective. This can raise a 
not-really-needed bits in the `needed` mask, so that for all subsequent 
permissions from the collection with that unneeded bits in the mask, an 
expensive fp.impliesIgnoreMask(fperm) will be executed.

The fix does not change the behavior, but helps avoid unnecessary calls 
to impliesIgnoreMask().

Would you please help review a trivial fix?

BUGURL: https://bugs.openjdk.java.net/browse/JDK-8230415
WEBREV: http://cr.openjdk.java.net/~igerasim/8230415/00/webrev/

Thanks in advance!

-- 
With kind regards,
Ivan Gerasimov