I'll have to look at the book again tomorrow (left it at work). On 14 September 2014 12:32, Ralph Goers <[email protected]> wrote:
> Yes, but take a look at the Effective Java section. What you coded works > correctly but it accesses “instance” twice. By reading instance into a temp > variable that isn’t volatile it claims you can get a bit of a performance > boost since the volatile variable is accessed only once. > > Ralph > > On Sep 14, 2014, at 10:10 AM, Matt Sicker <[email protected]> wrote: > > Because volatile works properly in Java 1.6? At least that's what I > gathered the last time I discussed this with Ralph. > > On 14 September 2014 09:39, Gary Gregory <[email protected]> wrote: > >> This looks like the double checked locking pattern but it does not use a >> temp result var. Any reason why it is not like the 'classic' DCL (see >> Effective Java item 71). >> >> Gary >> >> ---------- Forwarded message ---------- >> From: <[email protected]> >> Date: Sun, Sep 14, 2014 at 3:00 AM >> Subject: git commit: Lazily initialize singleton instances spawning >> threads. >> To: [email protected] >> >> >> Repository: logging-log4j2 >> Updated Branches: >> refs/heads/master b257c78af -> 2ce32db31 >> >> >> Lazily initialize singleton instances spawning threads. >> >> - See discussion in LOG4J2-819. >> >> >> Project: http://git-wip-us.apache.org/repos/asf/logging-log4j2/repo >> Commit: >> http://git-wip-us.apache.org/repos/asf/logging-log4j2/commit/2ce32db3 >> Tree: http://git-wip-us.apache.org/repos/asf/logging-log4j2/tree/2ce32db3 >> Diff: http://git-wip-us.apache.org/repos/asf/logging-log4j2/diff/2ce32db3 >> >> Branch: refs/heads/master >> Commit: 2ce32db31a53a07914cf620df25e4c6a7e4fbdba >> Parents: b257c78 >> Author: Matt Sicker <[email protected]> >> Authored: Sun Sep 14 02:00:12 2014 -0500 >> Committer: Matt Sicker <[email protected]> >> Committed: Sun Sep 14 02:00:12 2014 -0500 >> >> ---------------------------------------------------------------------- >> .../org/apache/logging/log4j/core/util/CachedClock.java | 11 ++++++++++- >> .../logging/log4j/core/util/CoarseCachedClock.java | 11 ++++++++++- >> 2 files changed, 20 insertions(+), 2 deletions(-) >> ---------------------------------------------------------------------- >> >> >> >> http://git-wip-us.apache.org/repos/asf/logging-log4j2/blob/2ce32db3/log4j-core/src/main/java/org/apache/logging/log4j/core/util/CachedClock.java >> ---------------------------------------------------------------------- >> diff --git >> a/log4j-core/src/main/java/org/apache/logging/log4j/core/util/CachedClock.java >> b/log4j-core/src/main/java/org/apache/logging/log4j/core/util/CachedClock.java >> index c4324c7..6dfb34c 100644 >> --- >> a/log4j-core/src/main/java/org/apache/logging/log4j/core/util/CachedClock.java >> +++ >> b/log4j-core/src/main/java/org/apache/logging/log4j/core/util/CachedClock.java >> @@ -28,7 +28,8 @@ import java.util.concurrent.locks.LockSupport; >> */ >> public final class CachedClock implements Clock { >> private static final int UPDATE_THRESHOLD = 0x3FF; >> - private static final CachedClock instance = new CachedClock(); >> + private static volatile CachedClock instance; >> + private static final Object INSTANCE_LOCK = new Object(); >> private volatile long millis = System.currentTimeMillis(); >> private volatile short count = 0; >> >> @@ -50,6 +51,14 @@ public final class CachedClock implements Clock { >> } >> >> public static CachedClock instance() { >> + // LOG4J2-819: use lazy initialization of threads >> + if (instance == null) { >> + synchronized (INSTANCE_LOCK) { >> + if (instance == null) { >> + instance = new CachedClock(); >> + } >> + } >> + } >> return instance; >> } >> >> >> >> http://git-wip-us.apache.org/repos/asf/logging-log4j2/blob/2ce32db3/log4j-core/src/main/java/org/apache/logging/log4j/core/util/CoarseCachedClock.java >> ---------------------------------------------------------------------- >> diff --git >> a/log4j-core/src/main/java/org/apache/logging/log4j/core/util/CoarseCachedClock.java >> b/log4j-core/src/main/java/org/apache/logging/log4j/core/util/CoarseCachedClock.java >> index 77ffa4d..9fa7b15 100644 >> --- >> a/log4j-core/src/main/java/org/apache/logging/log4j/core/util/CoarseCachedClock.java >> +++ >> b/log4j-core/src/main/java/org/apache/logging/log4j/core/util/CoarseCachedClock.java >> @@ -23,7 +23,8 @@ import java.util.concurrent.locks.LockSupport; >> * the cost of some accuracy. >> */ >> public final class CoarseCachedClock implements Clock { >> - private static final CoarseCachedClock instance = new >> CoarseCachedClock(); >> + private static volatile CoarseCachedClock instance; >> + private static final Object INSTANCE_LOCK = new Object(); >> // ignore IDE complaints; volatile long is fine >> private volatile long millis = System.currentTimeMillis(); >> >> @@ -50,6 +51,14 @@ public final class CoarseCachedClock implements Clock { >> * @return the singleton instance >> */ >> public static CoarseCachedClock instance() { >> + // LOG4J2-819: use lazy initialization of threads >> + if (instance == null) { >> + synchronized (INSTANCE_LOCK) { >> + if (instance == null) { >> + instance = new CoarseCachedClock(); >> + } >> + } >> + } >> return instance; >> } >> >> >> >> >> >> -- >> E-Mail: [email protected] | [email protected] >> Java Persistence with Hibernate, Second Edition >> <http://www.manning.com/bauer3/> >> JUnit in Action, Second Edition <http://www.manning.com/tahchiev/> >> Spring Batch in Action <http://www.manning.com/templier/> >> Blog: http://garygregory.wordpress.com >> Home: http://garygregory.com/ >> Tweet! http://twitter.com/GaryGregory >> > > > > -- > Matt Sicker <[email protected]> > > > -- Matt Sicker <[email protected]>
