Re: help!

Hi Jan

Sorry, but something it's going wrong... I just did a git clone pl-devel
(after removing previous), but ./prepare fails...

...
Cloning into packages/xpce...
remote: Counting objects: 38173, done.
remote: Compressing objects: 100% (7320/7320), done.
remote: Total 38173 (delta 30908), reused 37568 (delta 30465)
Receiving objects: 100% (38173/38173), 13.63 MiB | 827 KiB/s, done.
Resolving deltas: 100% (30908/30908), done.
fatal: reference is not a tree: 0a4610459faf0eae5714da4f619e50517112e467
Unable to checkout '0a4610459faf0eae5714da4f619e50517112e467' in submodule
path 'packages/xpce'
The following submodules are not up-to-date
   packages/xpce
Do you want me to run git submodule update?

If I answer yes, (note, I already answered yes to same question immediately
after ./prepare) it continue with documentation.
But xpce it's the patched one, I feel I will not get an updated source
tree...





2014/1/22 Carlo Capelli <[email protected]>

>
>
>
> 2014/1/22 Jan Wielemaker <[email protected]>
>
>> Hi Carlo,
>>
>>
>> On 01/21/2014 10:28 AM, Carlo Capelli wrote:
>>
>>> Hi Jan
>>>
>>> Sorry to bother you, but I was trying to understand why I can't catch
>>> exceptions when calling on background thread, and stumbled upon a weird
>>> behaviour of the standard - not Qt - console.
>>>
>>> Briefly, ?- help. hangs.
>>>
>>> carlo@ubuntu-carlo-64:~$ swipl
>>> % .plrc compiled 0.07 sec, 1,574 clauses
>>> Welcome to SWI-Prolog (Multi-threaded, 64 bits, Version 7.1.5-DIRTY)
>>> Copyright (c) 1990-2013 University of Amsterdam, VU Amsterdam
>>> SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
>>> and you are welcome to redistribute it under certain conditions.
>>> Please visit http://www.swi-prolog.org for details.
>>>
>>> For help, use ?- help(Topic). or ?- apropos(Word).
>>>
>>> ?- help.
>>> ^C^C
>>> [forced] Action (h for help) ? goals
>>>   [23] pce_principal:send(@2182115/pui_toc, root(toc_folder('Manual',
>>> manual, resource(manual), resource(book))))
>>>   [20] pce_principal:new(_G6283, pui_toc)
>>>   [19] Send-method on @pui_help_window/pui_manual:
>>> pui_manual->table_of_contents
>>>   [17] pce_principal:send(@pui_help_window/pui_manual,
>>> table_of_contents)
>>>   [14] pce_principal:send(new(@pui_help_window/pui_manual, pui_manual),
>>> open)
>>>
>>> [forced] Action (h for help) ?
>>>
>>> Note the double ^C...
>>>
>>
>> I can't reproduce that.  Looks like a deadlock.  Note that xpce is not
>> multi-threaded.  It has a big lock around all its operations to make it
>> thread-safe.  There is in_pce_thread/1 to run asynchronously in the
>> pce thread.
>>
>> If the default behaviour is as above, either your compilation is
>> corrupted or you have something in your ~/.plrc that breaks this.
>>
>>
>>  In Qt console, win_menu:help, called on background, hangs, and the main
>>> thread got confused, hangs itself... It's a bit unfortunate, as this is
>>> probably one of the first menu a casual user will try...
>>>
>>
>> I submitted a patch for xpce to use in_pce_thread/1 for help/0 and quite
>> a few others.  This might fix this.
>>
>>
> Thanks Jan, going to try immediately...
>
>
>>  Since I hope the problems are (at least loosely) related, I wonder if
>>> some
>>> setting from C side could inhibit exceptions from working. Seems related
>>> to
>>> threading, since try {} catch {} works as expected in a simple setting
>>> (let's say, from main).
>>>
>>> BTW, the reason ?- help. doesn't work get explained after two abort...
>>>
>>> [forced] Action (h for help) ? abort
>>> ERROR: pce(object) `@pui_help_window' does not exist
>>>     Exception: (6) online_help:help ? abort
>>> % Execution Aborted
>>> ?- help.
>>>
>>> SWI-Prolog [thread 1]: received fatal signal 11 (segv)
>>> Stack trace labeled "crash":
>>>    [0] crashHandler+0x36
>>>    [1] dispatch_signal+0x44d
>>>    [2] __restore_rt+(nil)
>>>    [3] pthread_cond_signal+0xa
>>> Annullato
>>>
>>
>> Using ^C sends a Prolog signal.  These are handled synchronously at
>> a safe point in the execution.  Some foreign code simply blocks and
>> does not handle (Prolog) signals.  Now, if you hit ^C the second
>> time before the first one was honored, it will say [forced] and
>> call the interrupt handler directly from the C signal function
>> rather than through the Prolog signal handler.  If you abort, you
>> basically do a longjmp() out of the current environment, leaving
>> the system in an unknown state.  Anything may happen, in particular
>> if you break forcefully out of thread synchronization primitives
>> because these are not signal-safe.
>>
>>         Cheers --- Jan
>>
>>
>>
>
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