Re: Reliability and deadlock in Annex E/distributed code

["Dr. Adrian Wrigley" <amtw@linuxchip.demon.co.uk.uk.uk>]

On Tue, 12 Sep 2006 20:31:55 +0000, Dr. Adrian Wrigley wrote:

> On Sun, 10 Sep 2006 20:58:33 +0000, Dr. Adrian Wrigley wrote:
> 
>> I've been having difficulty getting my Annex E/glade code to run reliably.
>> 
>> Under gnat 3.15p for x86 Linux, things were tolerably OK, with failures
>> of the code about weekly (running one instance continuously).
>> Sometimes the program simply wouldn't allow new partitions to run, as if
>> there was some boot server failure.  Sometimes the server would suddenly
>> start consuming all the CPU cycles it could get.
> ...
> 
> OK.  I have produced a fairly short example.
> There are three partitions, A, B, C.
> C calls B which calls A.
> Compiler is GNAT GPL 2006 + GLADE 2006 on x86 Linux
> 
> The partition C (executable in ./cpart) runs OK on *alternate*
> invocations.  Every other time, it hangs indefinitely.
> This seems strange.

(talking to myself again...)

If I change function Next in b.adb so that it doesn't call A
(returning a constant instead),  there are absolutely no problems.
Only when B.Next calls A does the deadlock happen.

There must be something in BPart that isn't completing properly
when running B.Next and calling into A.  Each time the call into
B hangs, it uses up a task.  It will create anonymous tasks
to replace them until the whole program grinds to a halt :(

I've tried using gdb on BPart to see what's going on.  From
what I can tell, the key code is in s-rpcser.adb, function
RPC_Handler.  On alternate occasions, it executes the
remote subprogram or just stops.  If I could see why this
happens, I might be able to fix it...
--
Adrian