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world file access violation if LoadPlugin called during client startup

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Posted by Fiendish   USA  (1,746 posts)  [Biography] bio   Global Moderator
Date Thu 07 Dec 2017 08:30 PM (UTC)

Amended on Thu 07 Dec 2017 09:18 PM (UTC) by Fiendish

Message
If a plugin script section calls LoadPlugin before the world file is finished loading, it leads to an access violation reading the world file during startup. Would a possible solution be reading the plugin list fully and closing the world file before loading the plugins?

https://github.com/fiendish/aardwolfclientpackage
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Posted by Fiendish   USA  (1,746 posts)  [Biography] bio   Global Moderator
Date Reply #1 on Thu 07 Dec 2017 08:33 PM (UTC)

Amended on Thu 07 Dec 2017 08:34 PM (UTC) by Fiendish

Message
Follow-on bug.

Trying to work around the above, calling DoAfterSpecial(n, 'LoadPlugin(GetInfo(60).."myplugin.xml"', 12) instead of just LoadPlugin before the world is done loading causes a crash after n seconds.

https://github.com/fiendish/aardwolfclientpackage
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Posted by Fiendish   USA  (1,746 posts)  [Biography] bio   Global Moderator
Date Reply #2 on Thu 07 Dec 2017 09:01 PM (UTC)

Amended on Thu 07 Dec 2017 09:29 PM (UTC) by Fiendish

Message
You might wonder why LoadPlugin is being called so early. It's because I have it called from a Lua module as a way of adding a global alias and global OnPluginListChanged receiver (by way of plugin) if any plugin loads that module (because any OnPluginListChanged added inside the module might just get replaced by any defined in the plugin). It works fine while MUSHclient is up and running, but then throws the access violation errors during world startup when any requires are done at the top of a plugin script section as is fairly customary.

https://github.com/fiendish/aardwolfclientpackage
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Posted by Nick Gammon   Australia  (21,609 posts)  [Biography] bio   Forum Administrator
Date Reply #3 on Thu 07 Dec 2017 10:02 PM (UTC)
Message
Is this function call being done in the OnPluginInstall function, or outside any function (in global space)? That would change the execution order slightly.

- Nick Gammon

www.gammon.com.au, www.mushclient.com
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Posted by Fiendish   USA  (1,746 posts)  [Biography] bio   Global Moderator
Date Reply #4 on Thu 07 Dec 2017 10:58 PM (UTC)

Amended on Thu 07 Dec 2017 11:59 PM (UTC) by Fiendish

Message
Most people put requires at or near the beginning of the script section and don't fully understand the load and callback sequence, so I'm trying to make something that doesn't require redoing any logic in an existing plugin. So it could be called in OnPluginInstall, but it could also be called in the global space. I want to be able to say to someone "just put 'require foo' at the very beginning of your plugin's script section" so that they can use the contained methods and variables immediately.

I think I've managed to get around the errors by mimicing the reload plugin from inside itself thread (but wow is it convoluted):

   local action = [[DoAfterSpecial(0.1, 'require \'checkplugin\';do_plugin_check_now(\']]..theme_controller..[[\', \'aard_Theme_Controller\')', sendto.script)]]
   local prefix = GetAlphaOption("script_prefix")
   action = [[
      SetAlphaOption("script_prefix", "/")
      Execute("/]]..action:gsub("\\", "\\\\")..[[")
      SetAlphaOption("script_prefix", "]]..prefix:gsub("\\", "\\\\")..[[")
   ]]
   DoAfterSpecial(0.1, action, sendto.script)

https://github.com/fiendish/aardwolfclientpackage
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Posted by Nick Gammon   Australia  (21,609 posts)  [Biography] bio   Forum Administrator
Date Reply #5 on Fri 08 Dec 2017 12:12 AM (UTC)
Message
Can I clarify your workflow here?

You mention "require" so I presume you must have something like this:


Plugin_A (amongst others):


require "something.lua"


something.lua:


LoadPlugin(GetInfo(60).."myplugin.xml")
-- add a global alias to do something (what?)


myplugin.xml:


function OnPluginListChanged ()
  -- handle plugin list changing
end -- OnPluginListChanged

- Nick Gammon

www.gammon.com.au, www.mushclient.com
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Posted by Nick Gammon   Australia  (21,609 posts)  [Biography] bio   Forum Administrator
Date Reply #6 on Fri 08 Dec 2017 12:17 AM (UTC)
Message
I can't reproduce the crash by doing this:

This plugin is loaded already:


<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE muclient>

<muclient>
<plugin
   name="load_plugin_test"
   author="Nick Gammon"
   id="d3ecfab22afdeedb06b872f1"
   language="Lua"
   purpose="Tests a plugin loading another one"
   date_written="2017-12-08"
   requires="5.05"
   version="1.0"
   >

</plugin>

<script>
<![CDATA[
function OnPluginInstall ()
  ColourNote ("pink", "", "In OnPluginInstall inside plugin load_plugin_test")
  local result = LoadPlugin(GetInfo(60).."myplugin.xml")
  ColourNote ("pink", "", "Done load of myplugin.xml, got result " ..
              tostring (result) ..
              " (" .. error_desc [result] .. ")")
end -- OnPluginInstall
]]>
</script>
</muclient>


This one is not loaded (the above plugin loads it):


<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE muclient>

<muclient>
<plugin
   name="myplugin"
   author="Nick Gammon"
   id="1003ceffa695a1b0d11505c9"
   language="Lua"
   purpose="Tests a plugin being loaded by another one"
   date_written="2017-12-08"
   requires="5.05"
   version="1.0"
   >

</plugin>

<script>
<![CDATA[
function OnPluginInstall ()
  ColourNote ("pink", "", "In OnPluginInstall inside plugin myplugin.xml")
end -- OnPluginInstall
]]>
</script>
</muclient>

- Nick Gammon

www.gammon.com.au, www.mushclient.com
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Posted by Fiendish   USA  (1,746 posts)  [Biography] bio   Global Moderator
Date Reply #7 on Tue 27 Feb 2018 06:49 AM (UTC)

Amended on Tue 27 Feb 2018 06:50 AM (UTC) by Fiendish

Message
I propose that trying to load a plugin (see first post) that is already loaded shouldn't raise an error. And maybe that the xml file should be read and closed before plugins are begun loading.

See: https://imgur.com/a/b4TnH

https://github.com/fiendish/aardwolfclientpackage
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Posted by Nick Gammon   Australia  (21,609 posts)  [Biography] bio   Forum Administrator
Date Reply #8 on Wed 28 Feb 2018 12:07 AM (UTC)
Message
I don't quite see why you are getting a sharing violation on the main world file. When plugins are loaded they load with readOnly and shareDenyWrite which shouldn't cause an issue.

https://github.com/nickgammon/mushclient/blob/master/xml/xml_load_world.cpp#L875

Why would you get a sharing violation on opening the world file?

As far as I can see from MFC the main world document is also opened in the same way:


BOOL CDocument::OnOpenDocument(LPCTSTR lpszPathName)
{
	if (IsModified())
		TRACE0("Warning: OnOpenDocument replaces an unsaved document.\n");

	CFileException fe;
	CFile* pFile = GetFile(lpszPathName,
		CFile::modeRead|CFile::shareDenyWrite, &fe);


To be honest, the loading code is quite complex, and indeed the main world file is opened in MFC (as above) so I don't really have the option of closing it in advance of loading plugins.




Quote:

I propose that trying to load a plugin (see first post) that is already loaded shouldn't raise an error.


Are you suggesting that it should silently ignore attempts to reload the same plugin?

- Nick Gammon

www.gammon.com.au, www.mushclient.com
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Posted by Fiendish   USA  (1,746 posts)  [Biography] bio   Global Moderator
Date Reply #9 on Wed 28 Feb 2018 02:32 PM (UTC)

Amended on Wed 28 Feb 2018 03:44 PM (UTC) by Fiendish

Message
Quote:
Are you suggesting that it should silently ignore attempts to reload the same plugin?


What about something like...

-        if (m_CurrentPlugin->m_strID == p->m_strID)
-           ThrowErrorException ("The plugin '%s' is already loaded.", p->m_strName);
+        if ((m_CurrentPlugin->m_strID == p->m_strID) && (m_CurrentPlugin->m_strName != p->m_strName))
+           ThrowErrorException ("The UID of plugin '%s' conflicts with plugin '%s'.", m_CurrentPlugin->m_strName, p->m_strName);


or


-        if (m_CurrentPlugin->m_strID == p->m_strID)
-           ThrowErrorException ("The plugin '%s' is already loaded.", p->m_strName);
+        if (m_CurrentPlugin->m_strID == p->m_strID) {
+           if (m_CurrentPlugin->m_strName != p->m_strName)
+              ThrowErrorException ("The UID of plugin '%s' conflicts with plugin '%s'.", m_CurrentPlugin->m_strName, p->m_strName);
+           return;
+        }

https://github.com/fiendish/aardwolfclientpackage
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Posted by Nick Gammon   Australia  (21,609 posts)  [Biography] bio   Forum Administrator
Date Reply #10 on Wed 28 Feb 2018 10:00 PM (UTC)
Message
There's quite a complex call chain leading to plugins being loaded. We would have to back out of that for the duplicate plugin to some appropriate point.

For example, I think your change would fail on these lines:


    // if they really wanted a plugin, warn them if none found
    if ((iMask & XML_PLUGINS) && !m_CurrentPlugin)
      ThrowErrorException ("No plugin found");


- Nick Gammon

www.gammon.com.au, www.mushclient.com
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Posted by Fiendish   USA  (1,746 posts)  [Biography] bio   Global Moderator
Date Reply #11 on Thu 22 Mar 2018 03:48 PM (UTC)
Message
Quote:
Why would you get a sharing violation on opening the world file?

Probably because loading a new plugin tries to write to the file.

https://github.com/fiendish/aardwolfclientpackage
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Posted by Nick Gammon   Australia  (21,609 posts)  [Biography] bio   Forum Administrator
Date Reply #12 on Thu 22 Mar 2018 08:51 PM (UTC)
Message
Why would a plugin write to the world file? Is it trying to do a world save during initialization?

- Nick Gammon

www.gammon.com.au, www.mushclient.com
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Posted by Fiendish   USA  (1,746 posts)  [Biography] bio   Global Moderator
Date Reply #13 on Fri 23 Mar 2018 04:23 AM (UTC)
Message
Does LoadPLugin not add the plugin entry to the bottom of the world file?

https://github.com/fiendish/aardwolfclientpackage
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Posted by Nick Gammon   Australia  (21,609 posts)  [Biography] bio   Forum Administrator
Date Reply #14 on Fri 23 Mar 2018 04:33 AM (UTC)
Message
No, not directly. That would be part of the world saving process.

- Nick Gammon

www.gammon.com.au, www.mushclient.com
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