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    Parallel C program


    I'm making a parallel C program of matix mult with multiple processes . I am having difficulty in assigning various rows to different processes to compute . Can anyone help me with this ?
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    There are many ways to gut this fish, so the first thing you should look at are the constraints and specifications your instructor gives you. You might have each child process compute a row or compute a column of the output matrix. Suppose each child computes a row of the output. You could then provide each child process with a row to compute and both input matrices. However, this may not be the way your professor wants you to do this.
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    Suppose I have to create not more than 6 and then compute 20*20 matrix. That means one child process will compute more than one rows. Either I can make one process do more than one rows at a time and run them in parallel or I can make one row per process, making 6 rows compute at a time then doing sequentially and reusing those processes to do next 6. But I am baffled to construct it. Thanks :)
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    Originally Posted by adamant_387
    Either I can make one process do more than one rows at a time and run them in parallel or I can make one row per process, making 6 rows compute at a time then doing sequentially and reusing those processes to do next 6
    That second option doesn't even make sense. If you're limited to N processes just fairly divide up your M output rows among your N processes such that each process has at least M / N rows to compute, or if M is less than N just use M processes.

    Beyond this you need to show some code that demonstrates an attempt to implement this design.
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    Thanks , I know second one is feasible but I am unable to program it . For example , I have 11 rows M%N = 1 what will happen to this remaining row . Which process will take care of it. I am [trying to write code for it . It is not complete but shows intent of what I am trying to do . Please suggest some modifications.
    Code:
    #include <stdio.h>
    #include <sys/shm.h>
    #include <sys/stat.h>
    #include <sys/types.h>
    #include <unistd.h>
     
    #define MAX_PROC 10
    struct mul
    {
        float **first 
    	float **second
    	float **result
    	int m,n,p,q,row;
    	}
    int main()
    {
    	
    	int i,j,k;
    	int pid;
    	int shmid1,shmid2,shmid3,shmid4; // shared memory handler 
    	key_t key1,key2,key3; //key - name for sm(shared memory) area.
        char *shmfirst,*shmsecond,*shmresult,*shmstruct; 
        key1 = 123,key2=4644,key3=98883,key4=3874
    	 if ((shmid1 = shmget(key1,sizeof(struct mul), 0666)) < 0)  //create the sm area for matrix first
        { 
          perror("shmget"); 
          exit(1); 
        }
    	 if ((shmstruct = shmat(shmid1, NULL, 0)) == (char *) -1)  // attach it to the local address space and get the pointer to it: shmmul
        { 
          perror("shmat errorneous"); 
          exit(1); 
        } 
    	shmmul=(struct mul *)shmstruct; // struct object
    	 
    	 printf("Enter the number of rows and columns of first matrix\n");
         scanf("%d%d", &shmmul->m, &shmmul->n); 
    	
    	if ((shmid2 = shmget(key1,sizeof(first[shmmul->m][shmmul->n]),  0666)) < 0)  //create the sm area for matrix first
        { 
          perror("shmget"); 
          exit(1); 
        }
    	printf("Enter the number of rows and columns of second matrix\n");
         scanf("%d%d", &shmmul->p, &shmmul->q);
    	 if ((shmid3 = shmget(key2,sizeof(second[shmmul->p][shmmul->q]), 0666)) < 0)  //create the sm area for matrix second
        { 
          perror("shmget"); 
          exit(1); 
        }
    	if ((shmid4 = shmget(key3,sizeof(result[shmmul->m][shmul->q]),  0666)) < 0)  //create the sm area for result matrix
        { 
          perror("shmget"); 
          exit(1); 
        }
    	 
    	if ((shmfirst = shmat(shmid2, NULL, 0)) == (char *) -1)  // attach it to the local address space and get the pointer to it: first
        { 
          perror("shmat errorneous"); 
          exit(1); 
        } if ((shmsecond = shmat(shmid3, NULL, 0)) == (char *) -1)  // attach it to the local address space and get the pointer to it: second 
        { 
          perror("shmat errorneous"); 
          exit(1); 
        } if ((shmresult = shmat(shmid4, NULL, 0)) == (char *) -1)  // attach it to the local address space and get the pointer to it: third
        { 
          perror("shmat errorneous"); 
          exit(1); 
        } 
      
        
    	 shmmul->first= ((float*))shmfirst;
    	 shmmul->second= ((float*))shmsecond;
    	 shmmul->result= ((float*))shmresult;
    	 	   
    	 printf("Enter the elements of A matrix\n");
    			for( i = 0 ; i <shmmul-> m ; i++ )
    			 for ( j = 0 ; j < shmmul->n ; j++ )
    			  scanf("%f", &(shmmul->first[i][j]));
    	 printf("Enter the elements of A matrix\n");
    			for( i = 0 ; i <shmmul-> p ; i++ )
    			 for ( j = 0 ; j < shmmul->q; j++ )
    			  scanf("%f", &(shmmul->second[i][j]));
    	
    {
    for(i=0;i<shmmul->m;i++)
    {
    if (shmmul->m<MAX_PROC)
    fork();
    else 
    for(i=0;i<MAX_PROC;i++)
    {
    pid=fork();
    }
    if(pid=0)
    {
    	int x,j=0; 
    	 for(x=0;x<shmmul->q;x++)
       {
        sum=0.00;
    	int shmmul->row=i;
    	
    	for(j=0;j<;j++)
    	{
    		printf("%f %f %f \n", shmmul->first[shmmul->row][j], second[j][x],
                    first[shmmul->row][j] * second[j][x]);
    		sum += first[shmmul->row][j] * second[j][x]);
    	}
    	[shmmul->row][x] = sum;
       }
    }
    }
    }
     	 
    	 //destruction of the sm area:
    		shmdt(shmstruct); //detach the sm 
    		shmctl(shmid1, IPC_RMID, 0); //destroy it.
    shmdt(shmfirst); //detach the sm 
    		shmctl(shmid2, IPC_RMID, 0); //destroy it.
      shmdt(shmsecond); //detach the sm 
    		shmctl(shmid3, IPC_RMID, 0); //destroy it.
      shmdt(shmresult); //detach the sm 
    		shmctl(shmid4, IPC_RMID, 0); //destroy it.
    	
    }
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    IMO, you shouldn't be writing code using fork() until you've learnt how to indent code.

    Multi-threaded (or multi-process) code is hard enough to do when the code is nice and clean, but when it looks like dog-food to start with, then forget it.

    Code:
    #include <stdio.h>
    #include <sys/shm.h>
    #include <sys/stat.h>
    #include <sys/types.h>
    #include <unistd.h>
    
    #define MAX_PROC 10
    struct mul {
      float **first;
      float **second;
      float **result;
      int m, n, p, q, row;
    };
    
    int main()
    {
      int i, j, k;
      int pid;
      int shmid1, shmid2, shmid3, shmid4; // shared memory handler
      key_t key1, key2, key3;       //key - name for sm(shared memory) area.
      char *shmfirst, *shmsecond, *shmresult, *shmstruct;
      key1 = 123, key2 = 4644, key3 = 98883, key4 = 3874;
      if ((shmid1 = shmget(key1, sizeof(struct mul), 0666)) < 0)  //create the sm area for matrix first
      {
        perror("shmget");
        exit(1);
      }
    
      if ((shmstruct = shmat(shmid1, NULL, 0)) == (char *) -1)  // attach it to the local address space and get the pointer to it: shmmul
      {
        perror("shmat errorneous");
        exit(1);
      }
      shmmul = (struct mul *) shmstruct;  // struct object
    
      printf("Enter the number of rows and columns of first matrix\n");
      scanf("%d%d", &shmmul->m, &shmmul->n);
      if ((shmid2 = shmget(key1, sizeof(first[shmmul->m][shmmul->n]), 0666)) < 0) //create the sm area for matrix first
      {
        perror("shmget");
        exit(1);
      }
    
      printf("Enter the number of rows and columns of second matrix\n");
      scanf("%d%d", &shmmul->p, &shmmul->q);
      if ((shmid3 = shmget(key2, sizeof(second[shmmul->p][shmmul->q]), 0666)) < 0)  //create the sm area for matrix second
      {
        perror("shmget");
        exit(1);
      }
    
      if ((shmid4 = shmget(key3, sizeof(result[shmmul->m][shmul->q]), 0666)) < 0) //create the sm area for result matrix
      {
        perror("shmget");
        exit(1);
      }
    
      if ((shmfirst = shmat(shmid2, NULL, 0)) == (char *) -1) // attach it to the local address space and get the pointer to it: first
      {
        perror("shmat errorneous");
        exit(1);
      }
    
      if ((shmsecond = shmat(shmid3, NULL, 0)) == (char *) -1)  // attach it to the local address space and get the pointer to it: second
      {
        perror("shmat errorneous");
        exit(1);
      }
    
      if ((shmresult = shmat(shmid4, NULL, 0)) == (char *) -1)  // attach it to the local address space and get the pointer to it: third
      {
        perror("shmat errorneous");
        exit(1);
      }
    
      shmmul->first = ((float *)) shmfirst;
      shmmul->second = ((float *)) shmsecond;
      shmmul->result = ((float *)) shmresult;
    
      printf("Enter the elements of A matrix\n");
      for (i = 0; i < shmmul->m; i++)
        for (j = 0; j < shmmul->n; j++)
          scanf("%f", &(shmmul->first[i][j]));
    
      printf("Enter the elements of A matrix\n");
      for (i = 0; i < shmmul->p; i++)
        for (j = 0; j < shmmul->q; j++)
          scanf("%f", &(shmmul->second[i][j]));
    
      {
        for (i = 0; i < shmmul->m; i++) {
          if (shmmul->m < MAX_PROC)
            fork();
          else
            for (i = 0; i < MAX_PROC; i++) {
              pid = fork();
            }
          if (pid = 0) {
            int x, j = 0;
            for (x = 0; x < shmmul->q; x++) {
              sum = 0.00;
              int shmmul->row = i;
    
              for (j = 0; j <; j++) {
                printf("%f %f %f \n",
                       shmmul->first[shmmul->row][j], second[j][x],
                       first[shmmul->row][j] * second[j][x]);
                sum += first[shmmul->row][j] * second[j][x];
              }
              [shmmul->row][x] = sum;
            }
          }
        }
      }
    
      //destruction of the sm area:
      shmdt(shmstruct);             //detach the sm
      shmctl(shmid1, IPC_RMID, 0);  //destroy it.
      shmdt(shmfirst);              //detach the sm
      shmctl(shmid2, IPC_RMID, 0);  //destroy it.
      shmdt(shmsecond);             //detach the sm
      shmctl(shmid3, IPC_RMID, 0);  //destroy it.
      shmdt(shmresult);             //detach the sm
      shmctl(shmid4, IPC_RMID, 0);  //destroy it.
    }
    Second, if you're going to post code, then at least make sure it COMPILES, unless your question is about compiler error messages.
    Code:
    $ gcc -std=c99 -Wall -D_SVID_SOURCE foo.c
    foo.c: In function ‘main’:
    foo.c:22:42: error: ‘key4’ undeclared (first use in this function)
    foo.c:22:42: note: each undeclared identifier is reported only once for each function it appears in
    foo.c:26:5: warning: implicit declaration of function ‘exit’ [-Wimplicit-function-declaration]
    foo.c:26:5: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default]
    foo.c:32:5: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default]
    foo.c:34:3: error: ‘shmmul’ undeclared (first use in this function)
    foo.c:38:37: error: ‘first’ undeclared (first use in this function)
    foo.c:41:5: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default]
    foo.c:46:37: error: ‘second’ undeclared (first use in this function)
    foo.c:49:5: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default]
    foo.c:52:37: error: ‘result’ undeclared (first use in this function)
    foo.c:52:55: error: ‘shmul’ undeclared (first use in this function)
    foo.c:55:5: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default]
    foo.c:61:5: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default]
    foo.c:67:5: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default]
    foo.c:73:5: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default]
    foo.c:76:29: error: expected expression before ‘)’ token
    foo.c:77:30: error: expected expression before ‘)’ token
    foo.c:78:30: error: expected expression before ‘)’ token
    foo.c:98:7: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
    foo.c:101:11: error: ‘sum’ undeclared (first use in this function)
    foo.c:102:21: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘->’ token
    foo.c:102:21: error: expected expression before ‘->’ token
    foo.c:104:26: error: expected expression before ‘;’ token
    foo.c:110:11: error: expected expression before ‘[’ token
    foo.c:17:13: warning: unused variable ‘k’ [-Wunused-variable]
    There's nothing we can do to fix up this amount of problems, and have anything resembling what you want it to be.

    I changed a couple of things, but that was only to get indent to accept the program to format it.

    Third, I would suggest you start with a known working single-threaded program which does what you want without all the complication of processes and shared memory.

    In particular, put code into functions, so you don't have 100+ line of main() trying to do everything.

    So instead of this in main
    Code:
    for ( ... ) {
      for ( ... ) {
      }
    }
    You have
    Code:
    void calculate ( int i ) {
      for ( ... ) {
        for ( ... ) {
        }
      }
    }
    Which gets called from main as
    Code:
    for ( i = 0 ; i < 10 ; i++ ) {
        calculate(i);
    }
    So that when you come to make it multi-process, it becomes
    Code:
    for ( i = 0 ; i < 10 ; i++ ) {
        if ( fork() == 0 ) {
            calculate(i);
        }
    }
    If you think carefully about the interfaces you're going to need, you can smooth the way from single-process to multi-process with very little effort.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper
  12. #7
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    OH sorry about that , I will do the required changed and post it again ! That was a mess , I admit. I have compiled it though. I am trying to improve it. I don't know if I am going in right direction. I am getting an error:warning: incompatible implicit declaration of built-in function exit
    Code:
    #include <stdio.h>
    #include <sys/shm.h>
    #include <sys/stat.h>
    #include <sys/types.h>
    #include <unistd.h>
     
    #define MAX_PROC 10
    struct mul
    {
            float **first;
    	float **second;
    	float **result;
    	int m,n,p,q,row;
    	};
    	int main()
    {
    	
    	int i,j,k;
    	int pid;
    	int shmid1,shmid2,shmid3,shmid4; // shared memory handler 
           key_t key1,key2,key3,key4; //key - name for sm(shared memory) area.
        char *shmfirst,*shmsecond,*shmresult,*shmstruct; 
        key1 = 123,key2=4644,key3=98883,key4=3874;
    	 if ((shmid1 = shmget(key1,sizeof(struct mul), 0666)) < 0)  //create the sm area for matrix first
        { 
          perror("shmget"); 
          exit(1); 
        }
    	 if ((shmstruct = shmat(shmid1, NULL, 0)) == (char *) -1)  // attach it to the local address space and get the pointer to it: shmmul
        { 
          perror("shmat errorneous"); 
          exit(1); 
        } 
    	struct mul *shmmul=(struct mul *)shmstruct; // struct object
    	 
    	 printf("Enter the number of rows and columns of first matrix\n");
         scanf("%d%d", &shmmul->m, &shmmul->n); 
    	
    	if ((shmid2 = shmget(key1,sizeof(shmmul->first[shmmul->m][shmmul->n]),  0666)) < 0)  //create the sm area for matrix first
        { 
          perror("shmget"); 
          exit(1); 
        }
    	printf("Enter the number of rows and columns of second matrix\n");
         scanf("%d%d", &shmmul->p, &shmmul->q);
    	 if ((shmid3 = shmget(key2,sizeof(shmmul->second[shmmul->p][shmmul->q]), 0666)) < 0)  //create the sm area for matrix second
        { 
          perror("shmget"); 
          exit(1); 
        }
    	if ((shmid4 = shmget(key3,sizeof(shmmul->result[shmmul->m][shmmul->q]),  0666)) < 0)  //create the sm area for result matrix
        { 
          perror("shmget"); 
          exit(1); 
        }
    	 
    	if ((shmfirst = shmat(shmid2, NULL, 0)) == (char *) -1)  // attach it to the local address space and get the pointer to it: first
        { 
          perror("shmat errorneous"); 
          exit(1); 
        } if ((shmsecond = shmat(shmid3, NULL, 0)) == (char *) -1)  // attach it to the local address space and get the pointer to it: second 
        { 
          perror("shmat errorneous"); 
          exit(1); 
        } if ((shmresult = shmat(shmid4, NULL, 0)) == (char *) -1)  // attach it to the local address space and get the pointer to it: third
        { 
          perror("shmat errorneous"); 
          exit(1); 
        } 
      
        
    		shmmul->first= (float**)shmfirst;
    		shmmul->second= (float**)shmsecond;
    		shmmul->result= (float**)shmresult;
    	 	   
    	 printf("Enter the elements of  first matrix\n");
    			for( i = 0 ; i <shmmul-> m ; i++ )
    			 for ( j = 0 ; j < shmmul->n ; j++ )
    			  scanf("%f", &(shmmul->first[i][j]));
    	 printf("Enter the elements of second matrix\n");
    			for( i = 0 ; i <shmmul-> p ; i++ )
    			 for ( j = 0 ; j < shmmul->q; j++ )
    			  scanf("%f", &(shmmul->second[i][j]));
    	
    {
    for(i=0;i<shmmul->m;i++)
    {
    	if (shmmul->m<MAX_PROC)
    		fork();
    	else 
    		for(i=0;i<MAX_PROC;i++)
    	{
    		pid=fork();
    	}
    
    	if(pid == 0)
    	{
    		int x,j=0; 
    		for(x=0;x<shmmul->q;x++)
       {
       int sum;
        sum=0.00;
    	shmmul->row=i;
    	
    	for(j=0;j<q;j++)
    	{
    				printf("%f %f %f \n", shmmul->first[shmmul->row][j], shmmul->second[j][x],
                    shmmul->first[shmmul->row][j] * shmmul->second[j][x]);
    				sum += shmmul->first[shmmul->row][j] * shmmul->second[j][x];
    	}
    		shmmul->result[shmmul->row][x] = sum;
       }
    }
    }
    }

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