On Wednesday, 13 August 2014, Ralph Goers <ralph.go...@dslextreme.com> wrote:
> So are you going to change this back? > > Yeah I'll revert it unless someone else snags it first. I won't be at a computer for several hours, though. I would note that this is my relic of old Java development. Similar to the calls of size() > 0 instead of isEmpty() you still find all over the place. > Ralph > > On Aug 12, 2014, at 5:44 PM, Matt Sicker <boa...@gmail.com > <javascript:_e(%7B%7D,'cvml','boa...@gmail.com');>> wrote: > > Oh my bad, I mixed up lazy singleton and eager singleton. > > > On 12 August 2014 17:43, Ralph Goers <ralph.go...@dslextreme.com > <javascript:_e(%7B%7D,'cvml','ralph.go...@dslextreme.com');>> wrote: > >> Finally, see >> http://en.wikipedia.org/wiki/Singleton_pattern#Eager_initialization. >> This was the prior pattern which is clearly thread safe. >> >> Ralph >> >> On Aug 12, 2014, at 3:40 PM, Ralph Goers <ralph.go...@dslextreme.com >> <javascript:_e(%7B%7D,'cvml','ralph.go...@dslextreme.com');>> wrote: >> >> Let me put it another way. >> >> If your intent is that the factory should only be created when getManager >> is called vs when AbstractDataManager is loaded then your change is fine. >> However, I am not sure there is any benefit to that since I would expect >> every access to AbstractDataManager to be immediately followed by a call to >> getManager. >> >> From what I can see the previous code was not vulnerable to any race >> conditions. >> >> Ralph >> >> On Aug 12, 2014, at 3:33 PM, Ralph Goers <ralph.go...@dslextreme.com >> <javascript:_e(%7B%7D,'cvml','ralph.go...@dslextreme.com');>> wrote: >> >> So you are saying static initializers in a class can be executed multiple >> times? If so I certainly wasn’t aware of that and I would think a few >> pieces of code would need modification. Before I go searching can you >> point to something that says it works that way? >> >> When I read >> http://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom it >> indicates that static initialization IS guaranteed to be serial, in which >> case the holder pattern is not needed for this. That pattern is for when >> you want lazy initialization, not for guaranteeing a static variable is >> only initialized once. >> >> Ralph >> >> On Aug 12, 2014, at 1:13 PM, Ralph Goers <ralph.go...@dslextreme.com >> <javascript:_e(%7B%7D,'cvml','ralph.go...@dslextreme.com');>> wrote: >> >> What race condition? Static variables are initialized when the class is >> constructed. As far as I know there is no race condition on that or Java >> would be hosed. >> >> Ralph >> >> On Aug 12, 2014, at 12:07 PM, Matt Sicker <boa...@gmail.com >> <javascript:_e(%7B%7D,'cvml','boa...@gmail.com');>> wrote: >> >> Prevents multiple threads from constructing the field if they access the >> class concurrently. Basically, it prevents a race condition. The >> alternative is to make the field volatile and do a double-checked lock >> which we do in another class somewhere. >> >> >> On 12 August 2014 13:53, Gary Gregory <garydgreg...@gmail.com >> <javascript:_e(%7B%7D,'cvml','garydgreg...@gmail.com');>> wrote: >> >>> Hi, >>> >>> What is the justification for this extra level? >>> >>> Gary >>> >>> >>> -------- Original message -------- >>> From: mattsic...@apache.org >>> <javascript:_e(%7B%7D,'cvml','mattsic...@apache.org');> >>> Date:08/11/2014 22:04 (GMT-05:00) >>> To: comm...@logging.apache.org >>> <javascript:_e(%7B%7D,'cvml','comm...@logging.apache.org');> >>> Subject: svn commit: r1617397 - >>> /logging/log4j/log4j2/trunk/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/db/jdbc/JdbcDatabaseManager.java >>> >>> >>> Author: mattsicker >>> Date: Tue Aug 12 02:04:38 2014 >>> New Revision: 1617397 >>> >>> URL: http://svn.apache.org/r1617397 >>> Log: >>> Singleton pattern >>> >>> Modified: >>> >>> logging/log4j/log4j2/trunk/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/db/jdbc/JdbcDatabaseManager.java >>> >>> Modified: >>> logging/log4j/log4j2/trunk/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/db/jdbc/JdbcDatabaseManager.java >>> URL: >>> http://svn.apache.org/viewvc/logging/log4j/log4j2/trunk/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/db/jdbc/JdbcDatabaseManager.java?rev=1617397&r1=1617396&r2=1617397&view=diff >>> >>> ============================================================================== >>> --- >>> logging/log4j/log4j2/trunk/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/db/jdbc/JdbcDatabaseManager.java >>> (original) >>> +++ >>> logging/log4j/log4j2/trunk/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/db/jdbc/JdbcDatabaseManager.java >>> Tue Aug 12 02:04:38 2014 >>> @@ -36,7 +36,6 @@ import org.apache.logging.log4j.core.uti >>> * An {@link AbstractDatabaseManager} implementation for relational >>> databases accessed via JDBC. >>> */ >>> public final class JdbcDatabaseManager extends AbstractDatabaseManager { >>> - private static final JDBCDatabaseManagerFactory FACTORY = new >>> JDBCDatabaseManagerFactory(); >>> >>> private final List<Column> columns; >>> private final ConnectionSource connectionSource; >>> @@ -174,10 +173,19 @@ public final class JdbcDatabaseManager e >>> final >>> ColumnConfig[] columnConfigs) { >>> >>> return AbstractDatabaseManager.getManager( >>> - name, new FactoryData(bufferSize, connectionSource, >>> tableName, columnConfigs), FACTORY >>> + name, new FactoryData(bufferSize, connectionSource, >>> tableName, columnConfigs), getFactory() >>> ); >>> } >>> >>> + // the usual lazy singleton >>> + private static class Holder { >>> + private static final JDBCDatabaseManagerFactory INSTANCE = new >>> JDBCDatabaseManagerFactory(); >>> + } >>> + >>> + private static JDBCDatabaseManagerFactory getFactory() { >>> + return Holder.INSTANCE; >>> + } >>> + >>> /** >>> * Encapsulates data that {@link JDBCDatabaseManagerFactory} uses >>> to create managers. >>> */ >>> >>> >>> >> >> >> -- >> Matt Sicker <boa...@gmail.com >> <javascript:_e(%7B%7D,'cvml','boa...@gmail.com');>> >> >> >> >> >> >> > > > -- > Matt Sicker <boa...@gmail.com > <javascript:_e(%7B%7D,'cvml','boa...@gmail.com');>> > > > -- Matt Sicker <boa...@gmail.com>
