我面临一个问题：香港专业教育学院完成了mandelbrot的mpi版本，它完美无缺。然后我必须使用openmp实现混合版本。我已经在循环中将openmp并行化与所有计算（在函数calculoMandelbrot中）。如果我删除omp指令（omp for parallel和omp barrier），它的工作完美（这是我的mpi实现）。应该工作，但我不能猜测我迷路的地方。
我有一个IMAGEHEIGHT * IMAGEWIDTH的图像，每个过程都成为它的一部分（例如：如果我有一个100高度的图像，4个过程，每个过程计算25行，在calculoMandelbrot函数中完成）。然后我向主人发送一条消息，其中包含计算每个过程的部分结果。
结果的ppm是一团糟。不知道为什么......任何帮助都会被贬低......
/
// mandelbrot.c
//
//
// The Mandelbrot calculation is to iterate the equation
// z = z*z + c, where z and c are complex numbers, z is initially
// zero, and c is the coordinate of the point being tested. If
// the magnitude of z remains less than 2 for ever, then the point
// c is in the Mandelbrot set. In this code We write out the number of iterations
// before the magnitude of z exceeds 2, or UCHAR_MAX, whichever is
// smaller.//
//
//
#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
#include <omp.h>
#include <math.h>
#define TAG_ENVIO 3
int IMAGEWIDTH = 600;
int IMAGEHEIGHT = 400;
int ITERATIONS = 100000;
int CHUNK = 1;
int SIZE;
void escribirfichero(char* pixels) {
int i;
FILE *fp;
fp = fopen("MandelbrotSet.ppm", "w");
if (fp == NULL) {
perror ( "Unable to open file" );
exit (EXIT_FAILURE);
}
//printf("Empezamos a escribir en el fichero");
fprintf(fp, "P6\n# CREATOR: mandel program\n");
fprintf(fp, "%d %d\n255\n", IMAGEWIDTH, IMAGEHEIGHT);
for (i = 0; i < (IMAGEWIDTH*3*IMAGEHEIGHT); i++)
fputc((char) pixels[i],fp);
fclose(fp);
}
void calculoMandelbrot(char *destino, int iproc, int height)
{
int posInici = iproc * height;
int xactual, yactual;
int posLocal = 0;
int chunkSize = height * IMAGEWIDTH * 3;
omp_set_dynamic(1);
//each iteration, it calculates: newz = oldz*oldz + p, where p is the current pixel, and oldz stars at the origin
double pr, pi; //real and imaginary part of the pixel p
double newRe, newIm, oldRe, oldIm; //real and imaginary parts of new and old z
double zoom = 1, moveX = -0.5, moveY = 0; //you can change these to zoom and change position
int numcpu = omp_get_num_procs();
omp_set_num_threads(numcpu);
if(iproc != 0)
destino = (char *)malloc(sizeof(char) * chunkSize);
#pragma omp parallel //shared(moveX, moveY, zoom) private(xactual, yactual, pr, pi, newRe, newIm) if (numcpu>1)
{
#pragma omp for schedule(dynamic) //, CHUNK
for(yactual = posInici; yactual < posInici + height; yactual++)
{
for(xactual = 0; xactual < IMAGEWIDTH; xactual++)
{
//calculate the initial real and imaginary part of z, based on the pixel location and zoom and position values
pr = 1.5 * (xactual - IMAGEWIDTH / 2) / (0.5 * zoom * IMAGEWIDTH) + moveX;
pi = (yactual - IMAGEHEIGHT / 2) / (0.5 * zoom * IMAGEHEIGHT) + moveY;
newRe = newIm = oldRe = oldIm = 0; //these should start at 0,0
//"i" will represent the number of iterations
int i;
//start the iteration process
for(i = 0; i < ITERATIONS; i++)
{
//remember value of previous iteration
oldRe = newRe;
oldIm = newIm;
//the actual iteration, the real and imaginary part are calculated
newRe = oldRe * oldRe - oldIm * oldIm + pr;
newIm = 2 * oldRe * oldIm + pi;
//if the point is outside the circle with radius 2: stop
if((newRe * newRe + newIm * newIm) > 4) break;
}
if(i == ITERATIONS)
{
//escribirArray(destino, posLocal, 0, 0, 0);
destino[posLocal] = 0;
destino[++posLocal] = 0;
destino[++posLocal] = 0;
++posLocal; //me preparo para colocar siguiente.
}
else
{
double z = sqrt(newRe * newRe + newIm * newIm);
int brightness = 256 * log2(1.75 + i - log2(log2(z))) / log2((double)ITERATIONS);
//escribirArray(envioArr, xactual, yactual, brightness, brightness, 255);
destino[posLocal] = brightness;
destino[++posLocal] = brightness;
destino[++posLocal] = 255;
++posLocal; //me preparo para colocar siguiente
}
}
}
}
#pragma omp barrier
if(iproc != 0)
{
MPI_Send(destino, chunkSize, MPI_CHAR, 0, TAG_ENVIO, MPI_COMM_WORLD);
free(destino);
}
}
void stringCopy(char *pixels, char *reciboArr, int sender, int height)
{
int posInici = sender * height * IMAGEWIDTH*3;
int pos;
for (pos = 0; pos < height * IMAGEWIDTH*3; pos++, posInici++) {
pixels[posInici] = reciboArr[pos];
}
}
int main(int argc, char** argv) {
// mandelbrot
char* pixels;
// mpi
int nproc, iproc;
// calculos tiempo
double begin;
double end_calc;
double end_total;
if(argc >= 3)
{
// se supone que la línia de ejecucion sera del tipo
// -n 4 ${workspace_loc:MPI}/Debug/MPI${build_files} 100 200
// FALTA PROVAR EN MOORE
IMAGEWIDTH = atoi(argv[1]);
IMAGEHEIGHT = atoi(argv[2]);
}
if(argc == 4)
{
ITERATIONS = atoi(argv[3]);
}
if(argc == 5)
{
CHUNK = atoi(argv[4]);
}
SIZE = IMAGEHEIGHT * IMAGEWIDTH * 3;
if (MPI_Init(&argc, &argv) != MPI_SUCCESS) {
fprintf(stderr, "Error al inicializar MPI.\n");
return 100;
}
begin = MPI_Wtime();
if (MPI_Comm_size(MPI_COMM_WORLD, &nproc) != MPI_SUCCESS) {
fprintf(stderr, "No se puede obtener el contador de procesos.\n");
MPI_Finalize();
return 101;
} else if (nproc < 2) {
fprintf(stderr, "Se necesitan almenos 2 procesos (se usan %d)\n", nproc);
MPI_Finalize();
return 102;
}
if (MPI_Comm_rank(MPI_COMM_WORLD, &iproc) != MPI_SUCCESS) {
fprintf(stderr, "No se puede obtener el rango para el proceso.\n");
MPI_Finalize();
return 103;
}
if ((IMAGEHEIGHT % nproc) != 0)
{
printf("Incompatable number of processes requested\nExiting...\n");
exit(EXIT_FAILURE);
}
int height = IMAGEHEIGHT/nproc;
int chunkSize = height * IMAGEWIDTH * 3;
if (iproc != 0) {
char *envioArr = (char *)malloc(sizeof(char) * chunkSize);
calculoMandelbrot(envioArr, iproc, height);
}
else if(iproc == 0) {
printf("Empezando los calculos de Mandelbrot...\n");
printf("IMAGEWIDTH %d IMAGEHEIGHT %d ITERATIONS %d num procesos %d CHUNK %d\n", IMAGEWIDTH, IMAGEHEIGHT, ITERATIONS, nproc, CHUNK);
pixels = (char *)malloc(SIZE * sizeof(char));
calculoMandelbrot(pixels, iproc, height);
//inicio recibir el resto de mensajes
char *reciboArr = (char *)malloc(sizeof(char)*chunkSize);
int i;
MPI_Status status;
for (i = 1; i<nproc; i++)
{
MPI_Recv(reciboArr, height*IMAGEWIDTH*3, MPI_CHAR, MPI_ANY_SOURCE, TAG_ENVIO, MPI_COMM_WORLD, &status);
stringCopy(pixels, reciboArr, status.MPI_SOURCE, height);
}
free(reciboArr);
//final de recibir resto de mensajes
end_calc = MPI_Wtime() - begin;
printf("Tiempo en calculos: %.10lf segundos \n", end_calc);
//MPI_Barrier(MPI_COMM_WORLD);
//printf("Escribiendo la imagen\n");
escribirfichero(pixels);
end_total = MPI_Wtime() - begin;
printf("Tiempo en total: %.10lf segundos \n", end_total);
free(pixels);
}
MPI_Finalize();
return 0;
}
答案 0 :(得分：0)
如果有人遇到相同或类似的问题，解决方案是：
起点如问题所述，mpi版本工作正常（没有openmp条款）。在im debuggint的情况下，变量posLocal从0到180000（图像宽度* 3 *高度）变化： - IMAGEWIDTH值600 - 身高为100（IMAGEHEIGHT 400分为4个过程）
因此，当我介绍openmp条款时，并不确切地知道为什么使用open mp屏障，posLocal最终值被卡在175000或接近。 经过多次测试，我已经能够将posLocal带到180000，使得destino和posLocal共享，并且xactual和yactual是私有的。也许其他组合也可以，但这对我有用。
感谢coincoin的兴趣。
#pragma omp parallel shared ( destino) private ( xactual, yactual)
{
#pragma omp parallel for schedule(static)
for(yactual = posInici; yactual < posInici + height; yactual++)
{
for(xactual = 0; xactual < IMAGEWIDTH; xactual++)
{
//calculate the initial real and imaginary part of z, based on the pixel location and zoom and position values
pr = 1.5 * (xactual - IMAGEWIDTH / 2) / (0.5 * zoom * IMAGEWIDTH) + moveX;
pi = (yactual - IMAGEHEIGHT / 2) / (0.5 * zoom * IMAGEHEIGHT) + moveY;
newRe = newIm = oldRe = oldIm = 0; //these should start at 0,0
//"i" will represent the number of iterations
int i;
//start the iteration process
for(i = 0; i < ITERATIONS; i++)
{
//remember value of previous iteration
oldRe = newRe;
oldIm = newIm;
//the actual iteration, the real and imaginary part are calculated
newRe = oldRe * oldRe - oldIm * oldIm + pr;
newIm = 2 * oldRe * oldIm + pi;
//if the point is outside the circle with radius 2: stop
if((newRe * newRe + newIm * newIm) > 4) break;
}
//printf("Antes zona paralela: %d process Thread: %d \n", iproc, numcpu);
if(i == ITERATIONS)
{
//escribirArray(destino, posLocal, 0, 0, 0);
destino[posLocal] = 0;
destino[++posLocal] = 0;
destino[++posLocal] = 0;
++posLocal; //me preparo para colocar siguiente.
}
else
{
double z = sqrt(newRe * newRe + newIm * newIm);
int brightness = 256 * log2(1.75 + i - log2(log2(z))) / log2((double)ITERATIONS);
//escribirArray(envioArr, xactual, yactual, brightness, brightness, 255);
destino[posLocal] = brightness;
destino[++posLocal] = brightness;
destino[++posLocal] = 255;
++posLocal; //me preparo para colocar siguiente
}
}
}
}
#pragma omp barrier
printf("Despuess zona paralela: %d process Thread: %d y posLocal %d \n", iproc, numcpu, posLocal);
if(iproc != 0)
{
MPI_Send(destino, chunkSize, MPI_CHAR, 0, TAG_ENVIO, MPI_COMM_WORLD);
printf("Estoy enviando en el proceso: %d y la posLocal es %d \n", iproc, posLocal);
free(destino);
}