On 07/02/2014 05:30 PM, Peter Levart wrote:
Hi Claes,
Thank you for looking into this patch.
On 07/02/2014 04:39 PM, Claes Redestad wrote:
Hi Peter,
perhaps the synchronized(this)-block in NameServiceAddresses::get()
can be replaced with a ReentrantLock? Applying this on top of your
patch, I seem to improve scores on your benchmark for -t 4 by ~33% on
my machine:
Which test? I would be surprised that this change has any impact but
on "getByNameNegative" test which exhibits this lock at each iteration
(since negative caching is disabled by default). I'll check this
myself too.
Feel free to ignore this. I don't seem to be able to benchmark properly
today and was jumping to conclusions: rerunning with just a bit more
rigor did not reproduce the improvement. In fact it doesn't even seem to
benefit getByNameNegative. Perhaps you'll get different results.
Thanks.
/Claes
--- a/src/share/classes/java/net/InetAddress.java Wed Jul 02
14:47:40 2014 +0200
+++ b/src/share/classes/java/net/InetAddress.java Wed Jul 02
14:57:24 2014 +0200
@@ -42,6 +42,7 @@
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ConcurrentSkipListSet;
import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.locks.ReentrantLock;
import sun.security.action.*;
import sun.net.InetAddressCachePolicy;
@@ -763,6 +764,7 @@
private static final class NameServiceAddresses implements
Addresses {
private final String host;
private final InetAddress reqAddr;
+ private final ReentrantLock lock = new ReentrantLock();
NameServiceAddresses(String host, InetAddress reqAddr) {
this.host = host;
@@ -774,7 +776,8 @@
Addresses addresses;
// only one thread is doing lookup to name service
// for particular host at any time.
- synchronized (this) {
+ lock.lock();
+ try {
// re-check that we are still us + re-install us if
slot empty
addresses = cache.putIfAbsent(host, this);
if (addresses == null) {
@@ -822,10 +825,13 @@
return inetAddresses;
}
// else addresses != this
+
+ // delegate to different addresses when we are
already replaced
+ // but outside of synchronized block to avoid any
chance of dead-locking
+ return addresses.get();
+ } finally {
+ lock.unlock();
}
- // delegate to different addresses when we are already
replaced
- // but outside of synchronized block to avoid any chance
of dead-locking
- return addresses.get();
}
}
nit: line 1258: getAddressesFromNameService made package private but
not used outside of InetAddress?
Good catch. I seem to have inadvertently deleted the "private" keyword.
Generally I think this looks good, but I'm not a reviewer. :)
/Claes
Regards, Peter
On 07/02/2014 01:56 PM, Peter Levart wrote:
Hi,
I updated the webrev with first two suggestions from Bernd
(expireTime instead of createTime and cacheNanos + only use
putIfAbsent instead of get followed by putIfAbsent):
http://cr.openjdk.java.net/~plevart/jdk9-dev/InetAddress.Cache/webrev.02/
Thanks, Bernd.
The id field in CachedAddresses is necessary for compareTo to never
return 0 for two different instances (used as element in
ConcurrentSkipListSet).
For last two suggestions I'm not sure whether they are desired, so
I'm currently leaving them as is.
Regards, Peter
On 07/01/2014 10:06 PM, Bernd Eckenfels wrote:
Looks good, like it, Peter.
some nits: instead of adding createTime and cacheNanos, only have a
expireAfter?
L782: is it better to use putIfAbsent unconditionally, instead of
get/putIfAbsent in NameServicdeAddr?
L732: I am unsure about the id field, isnt it enough to have the
identity equality check for the replacement check and otherwise depend
on equals()?
L1223: What about moving the cache exiry inside the if (useCache)
BTW1: might be the wrong RFR, but considering your good performance
numbers for an active cache, would having 100ms or similiar default
negative cache time make sense without impacting (visible) the
semantic.
Gruss
Bernd
Am Tue, 01 Jul 2014 20:35:57 +0200
schrieb Peter Levart <peter.lev...@gmail.com>:
Hi,
I propose a patch for this issue:
https://bugs.openjdk.java.net/browse/JDK-7186258
The motivation to re-design caching of InetAddress-es was not this
issue though, but a desire to attack synchronization bottlenecks in
methods like URL.equals and URL.hashCode which use host name to IP
address mapping. I plan to tackle the synchronization in URL in a
follow-up proposal, but I wanted to 1st iron-out the "leaves" of the
call-tree. Here's the proposed patch:
http://cr.openjdk.java.net/~plevart/jdk9-dev/InetAddress.Cache/webrev.01/
sun.net.InetAddressCachePolicy:
- two static methods (get() and getNegative()) were synchronized.
Removed synchronization and made underlying fields volatile.
- also added a normalization of negative policy in
setNegativeIfNotSet(). The logic in InetAddress doesn't cope with
negative values distinct from InetAddressCachePolicy.FOREVER (-1), so
this was a straight bug. The setIfNotSet() doesn't need this
normalization, because checkValue() throws exception if passed-in
value < InetAddressCachePolicy.FOREVER.
java.net.InetAddress:
- complete redesign of caching. Instead of distinct Positive/Negative
caches, there's only one cache - a ConcurrentHashMap. The value in
the map knows if it contains positive or negative answer.
- the design of this cache is similar but much simpler than
java.lang.reflect.WeakCache, since it doesn't have to deal with
WeakReferences and keys are simpler (just strings - hostnames).
Similarity is in how concurrent requests for the same key (hostname)
are synchronized when the entry is not cached yet, but still avoid
synchronization when entry is cached. This preserves the behaviour of
original InetAddress caching code but simplifies it greatly (100+
lines removed).
- I tried to preserve the interaction between
InetAddress.getLocalHost() and InetAddress.getByName(). The
getLocalHost() caches the local host address for 5 seconds privately.
When it expires it performs new name service look-up and "refreshes"
the entry in the InetAddress.getByName() cache although it has not
expired yet. I think this is meant to prevent surprises when
getLocalHost() returns newer address than getByName() which is called
after that.
- I also fixed the JDK-7186258 as a by-product (but don't know yet
how to write a test for this issue - any ideas?)
I created a JMH benchmark that tests the following methods:
- InetAddress.getLocalHost()
- InetAddress.getByName() (with positive and negative answer)
Here're the results of running on my 4-core (8-threads) i7/Linux:
http://cr.openjdk.java.net/~plevart/jdk9-dev/InetAddress.Cache/InetAddress.Cache_bench_results.01.pdf
The getByNameNegative() test does not show much improvement in
patched vs. original code. That's because by default the policy is to
NOT cache negative answers. Requests for same hostname to the
NameService(s) are synchronized. If
"networkaddress.cache.negative.ttl" system property is set to some
positive value, results are similar to those of getByNamePositive()
test (the default policy for positive caching is 30 seconds).
I ran the jtreg tests in test/java/net and have the same score as
with original unpatched code. I have 3 failing tests from original
and patched runs:
JT Harness : Tests that failed
java/net/MulticastSocket/Promiscuous.java: Test for interference when
two sockets are bound to the same port but joined to different
multicast groups
java/net/MulticastSocket/SetLoopbackMode.java: Test
MulticastSocket.setLoopbackMode
java/net/MulticastSocket/Test.java: IPv4 and IPv6 multicasting broken
on Linux
And 1 test that had error trying to be run:
JT Harness : Tests that had errors
java/net/URLPermission/nstest/lookup.sh:
Because of:
test result: Error. Can't find source file: jdk/testlibrary/*.java in
directory-list:
/home/peter/work/hg/jdk9-dev/jdk/test/java/net/URLPermission/nstest
/home/peter/work/hg/jdk9-dev/jdk/test/lib/testlibrary
All other 258 java/net tests pass.
So what do you think?
Regards, Peter
