Hi Doug, On 06/19/2014 02:02 PM, Doug Lea wrote:
On 06/19/2014 04:48 AM, Peter Levart wrote:
Or, even better, why not just using the next value from the "seeder" sequence for the initial value of "secondary" seed and avoid interaction with TLR's main seed/probe:
Thanks! Or better, just use mix32:
+ if ((r = (int)mix64(seeder.getAndAdd(SEEDER_INCREMENT))) == 0)
=> if ((r = mix32(seeder.getAndAdd(SEEDER_INCREMENT))) == 0)
That's right.
I committed this to jsr166 cvs. As you noted, this only addresses an uncommon performance glitch.
Not so performance as the "expected" behaviour. I'm assuming the aim of TLR.nextSecondarySeed() as a java.util.concurrent private thread-local source of random numbers is: - enough quality for it's purpose - fast - does not "disturb" the sequence of the primary public TLR sequence. I was concerned about the last point only.
I don't have any further ideas since we discussed last year the tradeoffs between computing decent quality initial seeds versus class-loading. I still think we have the best practical compromise in place.
This pertains to the other thread (ThreadLocalRandom clinit troubles) started by Martin Buchholz, right? He's making a valid point. The "seeder" static field is still uninitialized during either NetworkInterface class initialization (as a result of NetworkInterface.getNetworkInterfaces() call) or during SecureRandom.getSeed() call. Either of which can execute user code in some configurations which might in turn use ThreadLocalRandom. If this happens, TLR.current() throws a NPE. I proposed a re-arrangement of class initialization that allows TLR to be fully functional even during it's initialization, albeit with a less randomized seed, and does not change the behaviour otherwise (since it triggers re-initialization at the end). See the proposed patch in the other thread. Regards, Peter
-Doug
} UNSAFE.putInt(t, SECONDARY, r);
Regards, Peter
On 06/19/2014 10:37 AM, Peter Levart wrote:
Hi,
I noticed an inconsistency in calling TLR.localInit() method. Everywhere it's called conditionaly if thread-local "probe" is zero except in TLR.nextSecondarySeed() where it's called if "secondary" seed is zero. This re-initializes the "probe" and "seed" even though they might have already been initialized. It's not a big deal, because this happens at most once per thread, but it would be more consistent to call localInit() conditionaly, I think:
diff -r 5b45a5efe417 src/share/classes/java/util/concurrent/ThreadLocalRandom.java --- a/src/share/classes/java/util/concurrent/ThreadLocalRandom.java Tue May 20 10:11:23 2014 +0400 +++ b/src/share/classes/java/util/concurrent/ThreadLocalRandom.java Thu Jun 19 10:34:18 2014 +0200 @@ -1034,7 +1034,8 @@ r ^= r << 5; } else { - localInit(); + if (UNSAFE.getInt(t, PROBE) == 0) + localInit(); if ((r = (int)UNSAFE.getLong(t, SEED)) == 0) r = 1; // avoid zero }
Regards, Peter
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