Re: RE: svn commit: r1617397 - /logging/log4j/log4j2/trunk/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/db/jdbc/JdbcDatabaseManager.java
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=1617397r1=1617396r2=1617397view=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 ListColumn columns; private final ConnectionSource connectionSource; @@ -174,10 +173,19 @@ public final class JdbcDatabaseManager e
Re: RE: svn commit: r1617397 - /logging/log4j/log4j2/trunk/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/db/jdbc/JdbcDatabaseManager.java
On Wed, Aug 13, 2014 at 1:31 PM, Matt Sicker boa...@gmail.com wrote: 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. Matt, please do undo when you do get a chance. Gary 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 wrote: Oh my bad, I mixed up lazy singleton and eager singleton. On 12 August 2014 17:43, Ralph Goers 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 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 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 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 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 wrote: Hi, What is the justification for this extra level? Gary Original message From: mattsic...@apache.org Date:08/11/2014 22:04 (GMT-05:00) To: 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=1617397r1=1617396r2=1617397view=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 ListColumn 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
Re: RE: svn commit: r1617397 - /logging/log4j/log4j2/trunk/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/db/jdbc/JdbcDatabaseManager.java
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 wrote: Hi, What is the justification for this extra level? Gary Original message From: mattsic...@apache.org Date:08/11/2014 22:04 (GMT-05:00) To: 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=1617397r1=1617396r2=1617397view=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 ListColumn 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