Hello.. I am in the progress of parallelise a multi-agent model where "agents" are different instances (thousands) of a class and they have to independently perform a relatively cpu-intensive task (few seconds).
Looks the perfect situation for a reentrant code .... it seems...
My problem is that, even if I mutex.lock() all the should-be-concurrent code (for debugging reasons of course) my application crash, while if I use a single thread it works.
This is the code that I implemented so far:
Qt Code: 
  1. void
  2. Manager_farmers::landAllocation(){
  3. 	// .. serial code ..
  4.  
  5. 	for (int i=0; i < nThreads; i++){
  6. 		Manager_farmers_threads* wThread = new Manager_farmers_threads;
  7. 		wThreads.push_back(wThread);
  8. 	}
  9.  
  10. 	// parallelise the code to z workingThreads.. 
  11. 	for (uint y=0;y<myAgents.size();y++){
  12. 		bool assigned = false;
  13. 		while(!assigned) {
  14. 			for (uint z=0;z<wThreads.size();z++){
  15. 			  if (!wThreads[z]->isRunning()){
  16. 				wThreads[z]->assignJob(myAgents[y], freePlot);
  17. 				wThreads[z]->start();
  18. 				assigned = true;
  19. 				break;
  20. 			  }
  21. 			}
  22. 		}	
  23. 	}
  24.  
  25. 	// be sure that all threads are ended..
  26. 	for (int z=0; z < nThreads; z++){
  27. 		wThreads[z]->wait();
  28. 	}
  29.  
  30. 	// ..continue with serial code...
  31.  
  32. 	for (int i=0; i < nThreads; i++){
  33. 		delete wThreads[i]; // deleting the threads
  34. 	}
  35. }
  36.  
  37. void
  38. Manager_farmers_threads::assignJob(Agent_space* agent_h, const Pixel* plot_h){
  39. 	// .. this code shuld be run serialised by the main thread..
  40. 	agent = agent_h;
  41. 	plot = plot_h;
  42. 	agent->cachedOffer = 0;
  43. }
  44.  
  45. void
  46. Manager_farmers_threads::run(){
  47. 	// This code should be run parallelised...
  48. 	QMutex localMutex;
  49. 	localMutex.lock();
  50. 	agent->cachedOffer = agent->offerRentalPrice(plot);
  51. 	localMutex.unlock();
  52. }
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The question is.. why for hell it is crashing even if all the code is locked ?