I am trying to parallelize a C program which draws Mandelbrot set. I am dividing a section of the image for each processor in shape of equal-sized blocks as I have shown in this image:
I have tried to use the solution here which is almost addressing the same problem. However, I only get a partial image in output:
Also for high resolutions of the image (such as 8000x8000 pixels) the application crashes with segmentation fault 11. Here is my code:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
#include "mpi.h"
// Main program
int main(int argc, char* argv[])
{
/* screen ( integer) coordinate */
int iX,iY,i,j;
const int iXmax = 8000; // default
const int iYmax = 8000; // default
/* world ( double) coordinate = parameter plane*/
double Cx, Cy;
const double CxMin = -2.5;
const double CxMax = 1.5;
const double CyMin = -2.0;
const double CyMax = 2.0;
/* */
double PixelWidth = (CxMax - CxMin)/iXmax;
double PixelHeight = (CyMax - CyMin)/iYmax;
int linePerProcess, remainingLines, processMinY, processMaxY, lastProcessMaxY, result_offset;
int my_rank, processors, iXmaxHalf;
int startAlert = 1;
int receivedAlert;
unsigned char (*resultBuffer)[3] = NULL;
unsigned char (*resultBufferTwo)[3] = NULL;
unsigned char (*finalResultBuffer)[3] = NULL;
MPI_Status stat;
/* color component ( R or G or B) is coded from 0 to 255 */
/* it is 24 bit color RGB file */
const int MaxColorComponentValue = 255;
FILE * fp;
char *filename = "Mandelbrot.ppm";
char *comment = "# "; /* comment should start with # */
// RGB color array
unsigned char color[3];
/* Z = Zx + Zy*i; Z0 = 0 */
double Zx, Zy;
double Zx2, Zy2; /* Zx2 = Zx*Zx; Zy2 = Zy*Zy */
/* */
int Iteration;
const int IterationMax = 2000; // default
/* bail-out value , radius of circle ; */
const double EscapeRadius = 400;
double ER2 = EscapeRadius * EscapeRadius;
double startTime, endTime;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
MPI_Comm_size(MPI_COMM_WORLD, &processors);
linePerProcess = iYmax / (processors/2);
iXmaxHalf = iXmax / 2;
if (my_rank % 2 == 0) {
processMinY = (my_rank/2) * linePerProcess;
} else {
processMinY = ((my_rank - 1)/2) * linePerProcess;
}
processMaxY = processMinY + linePerProcess;
int Rows = iYmax; // Global array rows
int Columns = iXmax; // Global array columns
int sizes[2]; // No of elements in each dimension of the whole array
int subSizes[2]; // No of elements in each dimension of the subarray
int startCoords[2]; // Starting coordinates of each subarray
MPI_Datatype recvBlock, recvMagicBlock;
// Create a subarray (a rectangular block) datatype from a regular, 2d array
sizes[0] = Rows;
sizes[1] = Columns;
subSizes[0] = linePerProcess;
subSizes[1] = iXmaxHalf;
startCoords[0] = 0;
startCoords[1] = 0;
MPI_Type_create_subarray(2, sizes, subSizes, startCoords, MPI_ORDER_C, MPI_UNSIGNED_CHAR, &recvBlock);
MPI_Type_create_resized(recvBlock, 0, iXmaxHalf * sizeof(color), &recvMagicBlock);
MPI_Type_commit(&recvMagicBlock);
if (my_rank == 0) {
// startTime = MPI_Wtime();
// for(i=1; i<processors; i++){
// MPI_Send(&startAlert, 1, MPI_INT, i, 0, MPI_COMM_WORLD);
// }
// printf("rank; %d\n", my_rank);
finalResultBuffer = malloc(iXmax * iYmax * sizeof(color));
for(iY = processMinY; iY < processMaxY; iY++) {
Cy = CyMin + (iY * PixelHeight);
if (fabs(Cy) < (PixelHeight / 2))
{
Cy = 0.0; /* Main antenna */
}
for(iX = 0; iX < iXmaxHalf; iX++)
{
Cx = CxMin + (iX * PixelWidth);
/* initial value of orbit = critical point Z= 0 */
Zx = 0.0;
Zy = 0.0;
Zx2 = Zx * Zx;
Zy2 = Zy * Zy;
/* */
for(Iteration = 0; Iteration < IterationMax && ((Zx2 + Zy2) < ER2); Iteration++)
{
Zy = (2 * Zx * Zy) + Cy;
Zx = Zx2 - Zy2 + Cx;
Zx2 = Zx * Zx;
Zy2 = Zy * Zy;
};
/* compute pixel color (24 bit = 3 bytes) */
if (Iteration == IterationMax)
{
// Point within the set. Mark it as black
color[0] = 0;
color[1] = 0;
color[2] = 0;
}
else
{
// Point outside the set. Mark it as white
double c = 3*log((double)Iteration)/log((double)(IterationMax) - 1.0);
if (c < 1)
{
color[0] = 0;
color[1] = 0;
color[2] = 255*c;
}
else if (c < 2)
{
color[0] = 0;
color[1] = 255*(c-1);
color[2] = 255;
}
else
{
color[0] = 255*(c-2);
color[1] = 255;
color[2] = 255;
}
}
finalResultBuffer[(iY*iXmaxHalf)+iX][0] = color[0];
finalResultBuffer[(iY*iXmaxHalf)+iX][1] = color[1];
finalResultBuffer[(iY*iXmaxHalf)+iX][2] = color[2];
}
}
result_offset = 1;
for(i=1; i<processors; i++){
MPI_Recv(finalResultBuffer, 1, recvMagicBlock, i, 0, MPI_COMM_WORLD, &stat);
result_offset += 1;
}
} else if ((my_rank % 2 == 0) && (my_rank != 0)) {
// MPI_Recv(&receivedAlert, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, &stat);
// printf("rank; %d\n", my_rank);
resultBuffer = malloc(linePerProcess * iXmaxHalf * sizeof(color));
for(iY = processMinY; iY < processMaxY; iY++) {
Cy = CyMin + (iY * PixelHeight);
if (fabs(Cy) < (PixelHeight / 2))
{
Cy = 0.0; /* Main antenna */
}
for(iX = 0; iX < iXmaxHalf; iX++)
{
Cx = CxMin + (iX * PixelWidth);
/* initial value of orbit = critical point Z= 0 */
Zx = 0.0;
Zy = 0.0;
Zx2 = Zx * Zx;
Zy2 = Zy * Zy;
/* */
for(Iteration = 0; Iteration < IterationMax && ((Zx2 + Zy2) < ER2); Iteration++)
{
Zy = (2 * Zx * Zy) + Cy;
Zx = Zx2 - Zy2 + Cx;
Zx2 = Zx * Zx;
Zy2 = Zy * Zy;
};
/* compute pixel color (24 bit = 3 bytes) */
if (Iteration == IterationMax)
{
// Point within the set. Mark it as black
color[0] = 0;
color[1] = 0;
color[2] = 0;
}
else
{
// Point outside the set. Mark it as white
double c = 3*log((double)Iteration)/log((double)(IterationMax) - 1.0);
if (c < 1)
{
color[0] = 0;
color[1] = 0;
color[2] = 255*c;
}
else if (c < 2)
{
color[0] = 0;
color[1] = 255*(c-1);
color[2] = 255;
}
else
{
color[0] = 255*(c-2);
color[1] = 255;
color[2] = 255;
}
}
resultBuffer[((iY-processMinY)*iXmaxHalf)+iX][0] = color[0];
resultBuffer[((iY-processMinY)*iXmaxHalf)+iX][1] = color[1];
resultBuffer[((iY-processMinY)*iXmaxHalf)+iX][2] = color[2];
}
}
MPI_Send(resultBuffer, linePerProcess * iXmaxHalf, MPI_UNSIGNED_CHAR, 0, 0, MPI_COMM_WORLD);
free(resultBuffer);
} else {
// MPI_Recv(&receivedAlert, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, &stat);
// printf("rank; %d\n", my_rank);
resultBufferTwo = malloc(linePerProcess * iXmaxHalf * sizeof(color));
for(iY = processMinY; iY < processMaxY; iY++) {
Cy = CyMin + (iY * PixelHeight);
if (fabs(Cy) < (PixelHeight / 2))
{
Cy = 0.0; /* Main antenna */
}
for(iX = iXmaxHalf; iX < iXmax; iX++)
{
Cx = CxMin + (iX * PixelWidth);
/* initial value of orbit = critical point Z= 0 */
Zx = 0.0;
Zy = 0.0;
Zx2 = Zx * Zx;
Zy2 = Zy * Zy;
/* */
for(Iteration = 0; Iteration < IterationMax && ((Zx2 + Zy2) < ER2); Iteration++)
{
Zy = (2 * Zx * Zy) + Cy;
Zx = Zx2 - Zy2 + Cx;
Zx2 = Zx * Zx;
Zy2 = Zy * Zy;
};
/* compute pixel color (24 bit = 3 bytes) */
if (Iteration == IterationMax)
{
// Point within the set. Mark it as black
color[0] = 0;
color[1] = 0;
color[2] = 0;
}
else
{
// Point outside the set. Mark it as white
double c = 3*log((double)Iteration)/log((double)(IterationMax) - 1.0);
if (c < 1)
{
color[0] = 0;
color[1] = 0;
color[2] = 255*c;
}
else if (c < 2)
{
color[0] = 0;
color[1] = 255*(c-1);
color[2] = 255;
}
else
{
color[0] = 255*(c-2);
color[1] = 255;
color[2] = 255;
}
}
resultBufferTwo[((iY-processMinY)*iXmaxHalf)+(iX - iXmaxHalf)][0] = color[0];
resultBufferTwo[((iY-processMinY)*iXmaxHalf)+(iX - iXmaxHalf)][1] = color[1];
resultBufferTwo[((iY-processMinY)*iXmaxHalf)+(iX - iXmaxHalf)][2] = color[2];
// printf("rank: %d - value: %u%u%u\n", my_rank,resultBufferTwo[((iY-processMinY)*iXmax)+iX][0],resultBufferTwo[((iY-processMinY)*iXmax)+iX][1],resultBufferTwo[((iY-processMinY)*iXmax)+iX][2]);
}
}
MPI_Send(resultBufferTwo, iXmaxHalf * linePerProcess, MPI_UNSIGNED_CHAR, 0, 0, MPI_COMM_WORLD);
free(resultBufferTwo);
}
if (my_rank == 0) {
endTime = MPI_Wtime();
printf("Process time (s): %lf\n", endTime - startTime);
/*create new file,give it a name and open it in binary mode */
fp = fopen(filename, "wb"); /* b - binary mode */
/*write ASCII header to the file (PPM file format)*/
fprintf(fp,"P6\n %s\n %d\n %d\n %d\n", comment, iXmax, iYmax, MaxColorComponentValue);
for(iY = 0; iY < iYmax; iY++)
{
for(iX = 0; iX < iXmax; iX++)
{
fwrite(finalResultBuffer[(iY*iXmax)+iX], 1, 3, fp);
}
}
fclose(fp);
free(finalResultBuffer);
}
MPI_Finalize();
return 0;
}
I would appreciate it if someone could help me out to understand what I am doing wrong here.
