Hi Claes,
Haven't checked all changes yet, although it looks like a
straightforward swap of Properties for HashMap for intermediary result,
but I noticed the following in SystemProps:
265 var cmdProps = new HashMap<String,
String>((vmProps.length / 2) + Raw.FIXED_LENGTH);
The HashMap(int) constructor is different from Properties(int) in that
for the former, the argument represents the lower bound on the initial
size of the table (which is just a rounding of this parameter up to the
nearest power of 2). The threshold where the table is resized is
calculated as (initialCapacity rounded up to nearest power of 2) *
loadFactor. The default load factor is 0.75 which means that the table
will be resized in worst case after 3/4 * initialCapacity of elements
are inserted into it. In order to guarantee that the table is not
resized you have to pass (size * 4 + 2) / 3 to the HashMap constructor,
where size is the number of elements added...
I hope I'm not misleading you, I just think this is how HashMap has been
from the beginning. Peeking at HashMap code (line 693) it seems that it
is doing that:
float ft = (float)newCap * loadFactor;
newThr = (newCap < MAXIMUM_CAPACITY && ft <
(float)MAXIMUM_CAPACITY ?
(int)ft : Integer.MAX_VALUE);
newCap above is holding the initialCapacity constructor parameter
rounded up to the nearest power of 2. newThr is the threshold at which
the resize occurs.
The Properties(int) constuctor behaves differently as it passes the
parameter directly to the underlying ConcurrentHashMap, which says:
* @param initialCapacity The implementation performs internal
* sizing to accommodate this many elements.
Regards, Peter
On 12/10/18 10:17 PM, Claes Redestad wrote:
Hi,
by inverting the order in which the internal property maps are created,
we avoid some classloading and get a slightly more efficient code
execution profile in System.initPhase1.
Webrev: http://cr.openjdk.java.net/~redestad/8215159/jdk.00/
Bug: https://bugs.openjdk.java.net/browse/JDK-8215159
This reduces bytecode executed in initPhase1 from ~48k to ~36k. Not
much by any measure, but minimizing System.initPhase1 is important since
certain parts of the VM (JIT etc) are blocked from initializing until
it's done.
Thanks!
/Claes
