[jira] Updated: (NET-220) TFTPServer is not threadsafe

["Sebb (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/NET-220?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sebb updated NET-220:
---------------------

    Attachment: TFTPServerPathTest.patch
                TFTPServer.patch

Patch to TFTPServer changes all instance variables to final or volatile.

There did not seem to be a use-case for changing the logging destinations after construction, so rather than making these volatile (or adding synchronisation) I removed the set() methods.

The method used to start the server is called start(), but could of course be renamed if required.

> TFTPServer is not threadsafe
> ----------------------------
>
>                 Key: NET-220
>                 URL: https://issues.apache.org/jira/browse/NET-220
>             Project: Commons Net
>          Issue Type: Bug
>    Affects Versions: 2.0
>            Reporter: Sebb
>         Attachments: TFTPServer.patch, TFTPServerPathTest.patch
>
>
> The TFTPServer class is not threadsafe.
> There are several reasons for this:
> Ctors call private launch() method which creates a thread and start()s it.
> This publishes the instance before it has been fully constructed.
> Various instance fields are not thread-safe - e.g. serverReadDirectory_ is neither final nor volatile, and accesses to it are not synchronized. 
> Although it is only written by the ctors, the lack of synch means that the field may not be visible to other threads.
> As far as possible, instance fields should be made final - this guarantees that the field will be visible to other threads.
> One of the shutdown_ variables is volatile (so is threadsafe) but the shutdown_ variable in the nested TFTPTransfer class is not,  yet is accessed from multiple threads.
> The access to the variable serverException is not synch; should probably be volatile.
> Patch to follow.

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