decisionqueue.cpp

多核环境下运行了可满足性分析的工具软件

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MiraXT -- Copyright (c) 2007, Tobias Schubert, Matthew Lewis, Natalia Kalinnik, Bernd Becker 

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// Definition of the decision queue, needed to dynamically 
// divide the overall search space among the threads.
class DecisionQueue
{

private:

  int numThreads;              // Number of involved threads.
  int numWaitingThreads;       // Number of actual inactive threads, waiting for a new subproblem.
  int dqEI;                    // Decision Queue End Index, marking the end of the list of actual available subproblems.
  vec<vec<int> > DecsionQueue; // Array of decision stacks, conceptually similar to PSATO's "Guiding Paths".
 
  ControlStructure* masterControl;
  pthread_mutex_t decisionQueue_mutex;
  pthread_cond_t  decisionQueue_cond; 
				
public:

  // Constructor.
  DecisionQueue(int Threads, ControlStructure* control)   
  {
    numThreads        = Threads;
    masterControl     = control;
    dqEI              = 0;
    numWaitingThreads = 0;

    DecsionQueue.growTo(numThreads);    
    for(int i=0; i<numThreads; i++) { DecsionQueue[i].growTo(numLiterals); }
    
    pthread_mutex_init(&decisionQueue_mutex, NULL);
    pthread_cond_init(&decisionQueue_cond, NULL);
  }
  
  // Destructor.
  ~DecisionQueue(void)							
  {
    // Is there still an unevaluated subproblem left?
    if (dqEI != 0)
      {
	fprintf(stdout,"c Decision Queue Error: Unchecked subproblem(s) left\n");
	fprintf(stdout,"s UNKNOWN\n");

	// Exit code 0: UNKNOWN.
	exit(0);
      }
  }

  // Each SAT-solving thread periodically calls "needMoreDecisionStacks" to 
  // test if there is a need to divide its actual suproblem. 
  bool needMoreDecisionStacks(void)
  {
    // dqEI counts the number of available subproblems. If this number is
    // less than the number of currently waiting SAT-solving threads, another 
    // thread has to split its subproblem.
    if (dqEI < numWaitingThreads) { return true; } else { return false; }
  }

  // Used by the SAT-solving threads to divide their actual subproblem.
  void addDecisionStack(int& currentDL, int* DLLookupArray, int* DecisionStack)
  {
    pthread_mutex_lock(&decisionQueue_mutex);

    // Is there really a need for a new subproblem?
    if (dqEI < numWaitingThreads)
      {
	// Initialization.
	int i=0; int posDL1 = DLLookupArray[1];
    
	// Copy the thread's submitted decision stack into the decision queue.
	for (i=0; i<=posDL1; i++) { DecsionQueue[dqEI][i] = DecisionStack[i]; }
	
	// Flip the last variable assignment, so that the two problems are disjoint.
	// See also PSATO's concept of "Guiding Paths".
	DecsionQueue[dqEI][posDL1]   = DecsionQueue[dqEI][posDL1] ^ 1;

	// Use 0 to mark the end of the decision stack, since all literals have an index greater 0.
	DecsionQueue[dqEI][posDL1+1] = 0;
	
	// Update the "Decision Queue End Index".
	dqEI++;
	
	// Modify the submitting thread's actual decision stack, so that he is not allowed 
	// to search for an satisfiable assignment in the subproblem generated above.
	currentDL--; for (i=1; i<=currentDL; i++) { DLLookupArray[i] = DLLookupArray[i+1]; }	
      }
  
    pthread_cond_signal(&decisionQueue_cond);
    pthread_mutex_unlock(&decisionQueue_mutex);
  }

  // "getDecisionStack" can be used by any thread to get a new subproblem.
  bool getDecisionStack(int* newDecisionStack)
  {
    pthread_mutex_lock(&decisionQueue_mutex);

    // Increment the number of waiting threads.
    numWaitingThreads++;
 
    // Wait until a new subproblem is available (dqEI != 0), the end of the search has been 
    // signaled (masterDone != 0), or all threads are waiting (numWaitingThreads == numThreads).
    while(dqEI == 0 && masterControl->masterDone == 0 && numWaitingThreads != numThreads)
      { 
	// Wait for a signal that the current status has been changed.
	pthread_cond_wait(&decisionQueue_cond,&decisionQueue_mutex); 
      }

    // If all threads are waiting, then the search is over.
    if (numWaitingThreads == numThreads) 
      { masterControl->done(); }
    else
      {
	// New subproblem available?
	if (dqEI != 0)
	  {
	    dqEI--;
	    int L = 0;
	    while(DecsionQueue[dqEI][L] != 0) { newDecisionStack[L] = DecsionQueue[dqEI][L]; L++; }
	    newDecisionStack[L] = 0;
	  }
      }

    // Decrement the number of waiting threads.
    numWaitingThreads--;

    pthread_cond_signal(&decisionQueue_cond);
    pthread_mutex_unlock(&decisionQueue_mutex);

    // Is the search over?
    if (masterControl->masterDone != 0) { return false; }
    return true;
  }
};