[mkgmap-dev] [Patch] Spurious dead main thread

Sat Mar 3 16:06:59 GMT 2012

Hi WanMil,

I did never hit the problem that you describe. I don't think that this is
meant with
*approximately* correct result. I think the documentation just means that 
the calculation of the value happens at time x and the value is returned
*somewhat* 
later without blocking all other activities. So, between x and *somewhat*
later the thread 
might have finished.
On the other hand, we ask for the value and evaluate the loop condition
before 
calling take() again. I think this is another *somewhat* later.

Gerd

WanMil wrote
> 
> Hi Gerd,
> 
> thanks for the patch.
> The problem is the getActiveCount() method. The javadoc tells that it 
> returns the approximate number of active threads. The only chance that 
> the old code dead locks is that getActiveCount() returns 1 but all 
> threads have already been finished and all results have been taken via 
> the completion service.
> The patch fixes one problem (so I committed it) but as long as we cannot 
> guarantee that getActiveCount() returns the correct number of remaining 
> threads I expect that we might face a problem the other way round: One 
> or more jobs have not been completely finished but the loop exits 
> because getActiveCount() returns 0 (which is *approximately* correct...).
> 
> So I have to change that once more.
> 
> WanMil
> 
> 
>> Hi WanMil,
>>
>> the loop in  main (performance branch) does not always end, sometimes the
>> main thread hangs in cmplService.take();
>> I guess this happens when the last preparer finishes after the test of
>> getActiveCount() and before take() is called:
>>
>>
>> 			do {
>> 				try {
>> 					cmplService.take();
>> 				} catch (InterruptedException exp) {
>> 					System.err.println(exp.getMessage());
>> 				}
>> 			} while (((ThreadPoolExecutor) threadPool).getActiveCount()>  0);
>>
>> The attached patch solves this problem.
>>
>> Gerd
>> http://gis.19327.n5.nabble.com/file/n5533662/spuriois_hang.patch
>> spuriois_hang.patch
>>
>>
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