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From "Ralph Goers (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CONFIGURATION-496) Excessive Synchronization AbstractFileConfiguration
Date Tue, 08 May 2012 21:07:49 GMT

    [ https://issues.apache.org/jira/browse/CONFIGURATION-496?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13270831#comment-13270831
] 

Ralph Goers commented on CONFIGURATION-496:
-------------------------------------------

There is no simple answer to your question. Commons Configuration used to not be thread-safe.
Unfortunately, I discovered that after our application was already in production. My use case
deals with DefaultConfigurationBuilder constructing DynamicCombinedConfigurations and XMLConfigurations
all with file reloading.  Due to the way CombinedConfigurations work every time a configuration
file was reloaded other configurations that shared the common file were corrupted.

Unfortunately, you can't check to see if a reload is required without holding the lock or
multiple threads will end up performing the reload. 

All of this was put into place while the minimum version was Java 1.4. Now that it is Java
5 much of this code can be redone to take advantage of java.util.concurrent. I just haven't
gotten to it. However, I've had reports of similar issues from my users so I plan to  address
these issues in the very near future.
                
> Excessive Synchronization AbstractFileConfiguration
> ---------------------------------------------------
>
>                 Key: CONFIGURATION-496
>                 URL: https://issues.apache.org/jira/browse/CONFIGURATION-496
>             Project: Commons Configuration
>          Issue Type: Bug
>          Components: File reloading
>    Affects Versions: 1.6, 1.7, 1.8
>            Reporter: Tim Canavan
>
> We are having a problem with commons configuration 1.6 AbstractFileConfiguration 
> During a stress test we are seeing that we have wait locks against this method causing
this method not to complete for up to one second.
> We are using the FileReloadStrategy delegate which makes a check on the file system when
now + interval is greater than the compare time.
> Why can't we make this check before the synchronized block thus increasing throughput.
I have noticed in 1.8 that the caller to this method is synchronized. This seems like excessive
synchronization. Any ideas how to solve this. 
> {code}
> public void reload()
>     {
>         synchronized (reloadLock)
>         {
>             if (noReload == 0)
>             {
>                 try
>                 {
>                     enterNoReload(); // avoid reentrant calls
>                     if (strategy.reloadingRequired())
>                     {
>                         if (getLogger().isInfoEnabled())
>                         {
>                             getLogger().info("Reloading configuration. URL is " + getURL());
>                         }
>                         fireEvent(EVENT_RELOAD, null, getURL(), true);
>                         setDetailEvents(false);
>                         boolean autoSaveBak = this.isAutoSave(); // save the current
state
>                         this.setAutoSave(false); // deactivate autoSave to prevent information
loss
>                         try
>                         {
>                             clear();
>                             load();
>                         }
>                         finally
>                         {
>                             this.setAutoSave(autoSaveBak); // set autoSave to previous
value
>                             setDetailEvents(true);
>                         }
>                         fireEvent(EVENT_RELOAD, null, getURL(), false);
>                         // notify the strategy
>                         strategy.reloadingPerformed();
>                     }
>                 }
>                 catch (Exception e)
>                 {
>                     fireError(EVENT_RELOAD, null, null, e);
>                     // todo rollback the changes if the file can't be reloaded
>                 }
>                 finally
>                 {
>                     exitNoReload();
>                 }
>             }
>         }
>     }
> {code}

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