[Iterm-discuss] [PATCH] Work around a hang in Leopard

[Marc <ma...@da...>]

Hi folks,
after updating to Mac OS X 10.5.2 I experienced a huge problem with  
iTerm on my MacBook Pro (but not my iMac at work): after starting up  
iTerm hung up. The UI rendered, but upon trying to render the session  
nothing happened.

I then got the latest CVS version, but with the same problem. But in  
XCode I saw an error message regarding a deadlock in NSLock:

Thu Sep 25 20:34:52 neotokyo.local iTerm[14091] <Warning>:  
CGSResolveShmemReference : reference offset (65296) exceeds bounds  
(32768) on shmem obj 0x2f69
2008-09-25 20:34:52.793 iTerm[14091:10b] Error (1000) creating CGSWindow
2008-09-25 20:34:52.806 iTerm[14091:10b] *** -[NSLock lock]: deadlock  
(<NSLock: 0xfcccc0> '(null)')
2008-09-25 20:34:52.806 iTerm[14091:10b] *** Break on _NSLockError()  
to debug.

But it turned out that the deadlock was only the symptom, not the  
cause. After some googling, it seems that the "Error (1000) ..." stuff  
is a bug in Mac OS X 10.5.x. It's running inside code that is started  
with a [VT100Screen tryLock]. Because of the exception, the  
corresponding [VT100Screen releaseLock] is never called. Then the same  
thread later tries to run [VT100Screen acquireLock] and there you have  
your deadlock.

I traced the exception to PTYTextView::_renderChar (how do you write  
that in Objective-C syntax ?), more precisely to [image lockFocus].

The attached patch works around the bug by packing the [image  
lockFocus] into a @try @catch block. It retries the lockFocus up to  
five times. If that still does not work then the exception is  
rethrown. That fixes the hang problem for me.

Bye,
	Marc