>-----Original Message----- >From: Nathan Beyer [mailto:[EMAIL PROTECTED] >Sent: Thursday, December 07, 2006 6:01 AM >To: dev@harmony.apache.org >Subject: Re: [-SPAM-] RE: [classlib][swing] an odd code in swing > >On 12/6/06, Ivanov, Alexey A <[EMAIL PROTECTED]> wrote: >> >-----Original Message----- >> >From: Nathan Beyer [mailto:[EMAIL PROTECTED] >> >Sent: Wednesday, December 06, 2006 5:28 AM >> >To: dev@harmony.apache.org >> >Subject: Re: [-SPAM-] RE: [classlib][swing] an odd code in swing >> > >> >On 12/5/06, Thomas Hawtin <[EMAIL PROTECTED]> wrote: >> >> Ivanov, Alexey A wrote: >> >> > I think synchronized block can be safely removed. >> >> > Any way Swing is not thread-safe, and these methods are not >> explicitly >> >> > marked as thread-safe. >> >> >> >> This is a static mutable variables [bad]. In an environment where >> there >> >> are multiple 'AppContexts', such as Applets, it may be accessed by >> >> multiple threads. >> > >> >I've seen other unprotected (not synchronized) bits of code like this >> >that would seemingly need to be syncrhonized. I know the UI portions >> >of Swing must be thread isolated, but we can't assume that the >> >low-level services of Swing will be thread isolated, correct? >> >> Nathan, all, >> >> All Swing implementation is *thread-unsafe*. This is clearly stated in >> Javadocs and Swing tutorials. But there are several methods which are >> explicitly marked as thread-safe in Javadoc. And only such methods are >> guaranteed to be thread-safe. > >Do you know of any specific examples of code that's required to be thread >safe?
Yes, I do. For example: javax.swing.text.AbstractDocument.remove, .insertString, .createPosition; javax.swing.text.JTextComponent.replaceSelection, .setText. All these methods have the following comment: ====== quotation ======= This method is thread safe, although most Swing methods are not. Please see Threads and Swing [1] for more information. === end of quotation === There are other methods in swing.text which are required to be thread safe. There may be some in the UI part of Swing too. Regards, Alexey. [1] http://java.sun.com/products/jfc/swingdoc-archive/threads.html > >Other parts of the RI spec (the javadoc) aren't very good at >documenting all of the areas that are thread safe or the specifics of >it. > >-Nathan > >> >> Nothing is said about thread-safety in Timer doc, therefore in general >> you should call its methods only from the Event Dispatch Thread. >> Modifying timer object concurrently from several threads and even from >> any non-ED Thread is considered unsafe. Swing Timer calls its listeners >> on the EDT. >> >> >> Regards, >> Alexey. >> >> > >> >> >> >> >> From: Mikhail Loenko [mailto:[EMAIL PROTECTED] >> >> >> >> >> >> javax.swing.Timer >> >> >> >> >> >> this is an attomic operation, why synchronized? >> >> >> >> That is not a valid argument. >> >> >> >> One issue is that the change would not necessarily visible to other >> >> threads if not synchronized/volatile. Secondly, if there are other >> >> non-atomic operation using synchronized, then these may fail. >> However, >> >> in this case volatile looks fine, and no-one would really notice if >> even >> >> that was not present. >> > >> >Technically speaking, volatile would work, but I would lobby for >> >keeping it synchronized, as it will guarantee the atomicity and >> >ordering. Also, volatile has been notoriously incorrectly implemented >> >in VMs, as the memory model for the VM has only been completely >> >defined since Java 5. >> > >> >Good comments though. Java concurrency is a largely misunderstood >> >concept. If anyone's looking for a good book on it, Java Concurrency >> >in Practice is a great read. >> > >> >-Nathan >> > >> >-Nathan >> > >> >> >> >> >> public static void setLogTimers(final boolean isLogTimers) { >> >> >> synchronized (Timer.class) { >> >> >> Timer.isLogTimers = isLogTimers; >> >> >> } >> >> >> } >> >> >> >> Tom Hawtin >> >> >> >> -- >> Alexey A. Ivanov >> Intel Enterprise Solutions Software Division >> -- Alexey A. Ivanov Intel Enterprise Solutions Software Division
