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Bug 335399

Summary:	AbstractUIPlugin is not thread-safe
Product:	[Eclipse Project] Platform	Reporter:	Randy Hudson <hudsonr>
Component:	UI	Assignee:	Platform-UI-Inbox <Platform-UI-Inbox>
Status:	RESOLVED INVALID	QA Contact:
Severity:	normal
Priority:	P3	CC:	pwebster, remy.suen
Version:	3.6
Target Milestone:	---
Hardware:	PC
OS:	Mac OS X - Carbon (unsup.)
Whiteboard:

Description Randy Hudson

2011-01-25 18:24:22 EST

Methods like getImageRegistry can be called from any thread.  This method will lazily create a registry, but it is not thread-safe, so it may call createImageRegistry and initializeImageRegistry more than once.

Comment 1 Oleg Besedin

2011-01-26 10:53:04 EST

Please see the entry in the Eclipse help under
 Platform Plug-in Developer Guide > 
   Programmer's Guide > 
     Standard Widget Toolkit >
       Threading issues

Unless specified, all processing is assumed to be done on the UI thread.

Comment 2 Randy Hudson

2011-01-26 15:03:15 EST

Such a general statement like that is silly.  When you drive into the state of North Carolina, it says "Speed limit 55 unless otherwise posted", but good luck using that as an excuse for speeding.

If something must be done on the UI thread, you will see this in the javadoc:

 * @exception SWTException <ul>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread...

You can create images on any thread.  We are using SWT to render stuff onto Images on a server, which are then displayed by web browsers.  Our server has to handle multiple requests in parallel.  Making our code work on the server has been unnecessarily difficult.  I've had to create my own ThreadSafeResourceManager and other replacements.

Comment 3 Randy Hudson

2011-01-26 15:10:32 EST

The same help document also says "SWT will trigger an SWTException for any calls made from a non-UI thread that must be made from the UI thread".  Images are resources, but they are not UI. You can construct Images, Fonts, Colors, GCs, Patterns, Regions, and other resources on any thread.

Comment 4 Oleg Besedin

2011-01-26 16:04:19 EST

On the help page that I pointed to ( http://help.eclipse.org/helios/index.jsp?topic=/org.eclipse.platform.doc.isv/guide/swt_threading.htm )

please see this line:

"a platform UI library should not be considered thread-safe unless it is specifically documented as such".

This is a design principle for the Platform UI code. If you don't believe me, see bug 79492, bug 58315 .

In addition to that, OK, let's imagine we change AbstractUIPlugin#getImageRegistry() to be "thread-safe". What does that mean for the ImageRegistry class? Do we now need to make it thread-safe too? How about the following entry in its Javadoc:

 * An image registry owns all of the image objects registered
 * with it, and automatically disposes of them when the SWT Display
 * that creates the images is disposed. Because of this, clients do not 
 * need to (indeed, must not attempt to) dispose of these images themselves.

Comment 5 Randy Hudson

2011-01-27 17:06:21 EST

This is not an invalid request.  I've already have this working in my own code, and I verified with an SWT team member that threading restrictions only apply to the User Interface (UI), which includes Displays, and the Widget hierarchy.  Images are not UI.