Multithreading pthread errors - c

Question

Im trying to create a multithreaded application in C for Linux with pthreads library that makes an approximation of pi using infinite series with N+1 terms.Variable N and T are passed from the command line. I am using the Nilakantha approximation formula for pi. N is the upper limit of the number sequence to sum and T would be the # of child threads that calculate that sum. For example if I run command "./pie 100 4". The parent thread will create 4 child threads indexed 0 to 3. I have a global variable called vsum that is a double array allocated dynamically using malloc to hold values. So with 4 threads and 100 as the upper bound. My progam should compute:
Thread 0 computes the partial sum for i going from 0 to 24 stored to an element vsum[0]
Thread 1 computes the partial sum for i going from 25 to 49 stored to an element vsum[1]
Thread 2 computes the partial sum for i going from 50 to 74 stored to an element vsum[2]
Thread 3 computes the partial sum for i going from 75 to 99 stored to an element vsum[3]
After each thread makes calculations. The main thread will compute the sum by adding together all numbers from vsum[0] to vsum[T-1].
Im just starting to learn about threads and processes. Any help or advice would be appreciated. Thank you.
Code I wrote so far:
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
double *vsum;
int N, T;
void *PI(void *sum) //takes param sum and gets close to pi
{
int upper = (int)sum;
double pi = 0;
int k = 1;
for (int i = (N/T)*upper; i <= (N/T)*(upper+1)-1; i++)
{
pi += k*4/((2*i)*(2*i+1)*(2*i+2));
if(i = (N/T)*(upper+1)-1)
{
vsum[upper] = pi;
}
k++;
}
pthread_exit(0);
}
int main(int argc, char*argv[])
{
T = atoi(argv[2]);
N = atoi(argv[1]);
if (N<T)
{
fprintf(stderr, "Upper bound(N) < # of threads(T)\n");
return -1;
}
int pie = 0;
pthread_t tid[T]; //thread identifier
pthread_attr_t attr; //thread attributes
vsum = (double *)malloc(sizeof(double));//creates dyn arr
//Initialize vsum to [0,0...0]
for (int i = 0; i < T; i++){
{
vsum[i] = 0;
}
if(argc!=2) //command line does not give proper # of values
{
fprintf(stderr, "usage: commandline error <integer values>\n");
return -1;
}
if (atoi(argv[1]) <0) //if its is negative/sum error
{
fprintf(stderr, "%d must be >=0\n", atoi(argv[1]));
return -1;
}
//CREATE A LOOP THAT MAKES PARAM N #OF THREADS
pthread_attr_init(&attr);
for(int j =0; j < T;j++)
{
int from = (N/T)*j;
int to = (N/T)*(j+1)-1;
//CREATE ARRAY VSUM TO HOLD VALUES FOR PI APPROX.
pthread_create(&tid[j],&attr,PI,(void *)j);
printf("Thread %d computes the partial sum for i going from %d to %d stored to an element vsum[%d]\n", j, from, to, j);
}
//WAITS FOR THREADS TO FINISH
for(int j =0; j <T; i++)
{
pthread_join(tid[j], NULL);
}
//LOOP TO ADD ALL THE vsum array values to get pi approximation
for(int i = 0; i < T; i++)
{
pie += vsum[i];
}
pie = pie +3;
printf("pi computed with %d terms in %d threads is %d\n",N,T,pie);
vsum = realloc(vsum, 0);
pthread_exit(NULL);
return 0;
}
Here is the error I dont see that I get on my program: What am I missing here?
^
pie.c:102:1: error: expected declaration or statement at end of input
}
When I try to run my program I get the following:
./pie.c: line 6: double: command not found
./pie.c: line 7: int: command not found
./pie.c: line 8: int: command not found
./pie.c: line 10: syntax error near unexpected token `('
./pie.c: line 10: `void *PI(void *sum) //takes param sum and gets close to pi'

Answer 1

I haven't looked at logic of your code, but I see following programming errors.
Change
pthread_create(&tid[j],&attr,PI,j);
to
pthread_create(&tid[j],&attr,PI,(void *)j);
pthread_create() takes 4th param as void * which is passed to the thread function.
Also fix your thread function PI to use passed parameter as int like
void *PI(void *sum) //takes param sum and gets close to pi
{
int upper = (int)sum; //don't use `atoi` as passed param is int.
...
//your existing code
}
The 3rd error is for line
realloc(vsum, 0);
By passing 0 to re-allocate, you are effectively just freeing vsum, so you can just use free(vsum). If you indeed want to reallocate you should take the new allocated memory returned by the function something like vsum = realloc(vsum, 0);

Answer 2

The Syntax of pthread is
pthread_create(threadId, threadAttribute, callingMethodName, parameters of calling method);
Ex:
void printLetter( void *p)
{
int i=0;
char c=(char *)p;
while (i<10000)
{
printf("%c",c);
}
}
int main()
{
pthread_t thread_id;
char c='x';
pthread_create (&thread_id, NULL, &printLetter, &c);
pthread_join (thread_id, NULL);
return 0;
}
}