问题描述:

I am new to threading in C++ but I've done enough reading to at least get what I'm working on to compile. As of yet it hasn't improved performance at all. Right now I just have it creating the number of threads as there are loops but I can imagine that can pretty quickly cause the system to thrash. Is there a better alternative to brute force controlling the number of threads? I also intend to run this on the WestGrid computing system where I can specify the number of processors to use. What is the best way to set the number of threads to optimize for the number of processors.

void ExecuteCRTProcess(const long &numberOfRows, ZZ* rij, const ZZ &powRoh, const int &rowLength, long* PublicKey, ZZ* rQ0, const ZZ &Q0, ZZ* primes, const ZZ &productOfPrimes, ZZ* resultsArray, const bool IsItPrimeArray, long* caseStudy, long* caseStudyTracker, const ZZ &X0, const long &Roh){

int rc;

pthread_t threads[numberOfRows];

struct parameters ThreadParameters[numberOfRows];

for(int i = 0; i< numberOfRows ; i++){

FillR(rij,powRoh,rowLength); // fill up the vector rij with random numbers between 0 powRoh

MultiplyVectorByTwo(rij, rowLength, i, IsItPrimeArray); //Multiply rij vector by 2. If calculating Xi' also add 1 to appropriate values.

ThreadParameters[i].rij = rij;

ThreadParameters[i].rQ0 = rQ0;

ThreadParameters[i].primes = primes;

ThreadParameters[i].rowLength = rowLength;

ThreadParameters[i].Q0 = Q0;

ThreadParameters[i].i = i;

ThreadParameters[i].X0 = X0;

rc = pthread_create(&threads[i],NULL,CRTNew,(void *)&ThreadParameters[i]);

if(rc){

cout << "Error: unable to create thread, " << rc << endl;

exit(-1);

}

for(long j = 0; j< rowLength; j++){

cout << (resultsArray[i] % primes[j]) << " ";

}

cout << endl;*/

}

for(int i = 0; i< numberOfRows; i++){

pthread_join(threads[i], NULL);

resultsArray[i] = ThreadParameters[i].result;

}

}

The threads created run this function

void* CRTNew(void *threadArg){

struct parameters *local_data;

local_data = (struct parameters *) threadArg;

ZZ a, p, A, P, crt;

long Z, Public;

a = local_data->rQ0[local_data->i];

p = local_data->Q0;

A = local_data->rij[0];

P = local_data->primes[0];

for(int i = 1; i<=local_data->rowLength; i++){

A = A%P;

Z = CRT(a, p, A, P);

A = local_data->rij[i]; P = local_data->primes[i];

if(i == local_data->rowLength) Public = Z;

}

if(a < 0) crt = a+p;

else crt = a%p;

local_data->result = crt%local_data->X0;

pthread_exit(NULL);

}

网友答案:

'What is the best way to set the number of threads to optimize for the number of processors';

1) Create [num of cores] threads, (or maybe a few more), at app startup.

2) Never create any more threads

3) Never let the threads terminate.

4) Have them wait for work tasks on a producer-consumer thread, in the manner of a pool.

Alternatively, use a thread pool class or equivalent parallel language feature that already works.

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