Wsrtjtyk

I don't understand the man page for thread_create. What is a void * nullable? I can't make the array index a global variable for this program. The argument passed to the threads needs to be used in the fibonacci computation. I think somehow I need to get an index (or a pointer to an index) passed and processed by the thread to come up with a fibonacci computation. Here are my warnings:

fibonacci.c:46:31: warning: incompatible pointer types passing 'void *(int)' to parameter of type

      'void * _Nullable (* _Nonnull)(void * _Nullable)' [-Wincompatible-pointer-types]

                pthread_create(&thread, &a, run, i);

                                            ^~~

/usr/include/pthread.h:328:31: note: passing argument to parameter here

                void * _Nullable (* _Nonnull)(void * _Nullable),

                                            ^

fibonacci.c:46:36: warning: incompatible integer to pointer conversion passing 'int' to parameter

      of type 'void *' [-Wint-conversion]

                pthread_create(&thread, &a, run, i);

                                             ^

/usr/include/pthread.h:329:30: note: passing argument to parameter here

                void * _Nullable __restrict);

I originally made the index a global variable but was told that was not allowed because it makes the threads worthless. I'm not sure how else to modify the loop. The point of this program is an exercise in elementary multithreading, so I could use a mutex or semaphore, but I figured joining threads would be the simplest, but I can't figure out how to pass a purposeful argument to the threads. Any ideas? Here is my broken code:

#include<stdio.h> //for printf

#include<stdlib.h>  //for malloc

#include<pthread.h> //for threading



#define SIZE 25 //number of fibonaccis to be computed

int *fibResults;  //array to store fibonacci results



void *run(int arg)  //executes and exits each thread

{

  if (arg == 0)

  {

    fibResults[arg] = 0;

    printf("The fibonacci of %d= %dn", arg, fibResults[arg]);    

    pthread_exit(0); 

 }



  else if (arg == 1)

  {

    fibResults[arg] = 1;

    printf("The fibonacci of %d= %dn", arg, fibResults[arg]);   

    pthread_exit(0);  

  }

  else

  {

    fibResults[arg] = fibResults[arg -1] + fibResults[arg -2];

    printf("The fibonacci of %d= %dn", arg, fibResults[arg]);

    pthread_exit(0);

  }

}



//main function that drives the program.

int main()

{

  pthread_attr_t a;

  fibResults = (int*)malloc (SIZE * sizeof(int));

  pthread_attr_init(&a);



  for (int i = 0; i < SIZE; i++)

  {

    pthread_t thread;

    pthread_create(&thread, &a, run, i);

    printf("Thread[%d] createdt", i); 

    fflush(stdout);

    pthread_join(thread, NULL);

    printf("Thread[%d] joined & exitedt", i); 

  }

  return 0;

}

I'm trying to follow M.M.'s advice and I'm getting new errors and warnings with this code:

#include<stdio.h> //for printf

#include<stdlib.h>  //for malloc

#include<pthread.h> //for threading



#define SIZE 25 //number of fibonaccis to be computed

int *fibResults;  //array to store fibonacci results



void *run(void *arg)  //executes and exits each thread

{

  if (arg == 0)

  {

    fibResults[arg] = 0;

    printf("The fibonacci of %d= %dn", *arg, fibResults[*arg]);    

    pthread_exit(0); 

 }



  else if (arg == 1)

  {

    fibResults[*arg] = 1;

    printf("The fibonacci of %d= %dn", *arg, fibResults[*arg]);   

    pthread_exit(0);  

  }

  else

  {

    fibResults[*arg] = fibResults[*arg -1] + fibResults[*arg -2];

    printf("The fibonacci of %d= %dn", *arg, fibResults[*arg]);

    pthread_exit(0);

  }

}



//main function that drives the program.

int main()

{

  pthread_attr_t a;

  fibResults = (int*)malloc (SIZE * sizeof(int));

  pthread_attr_init(&a);



  for (int i = 0; i < SIZE; i++)

  {

    pthread_t thread;

    pthread_create(&thread, &a, run, &fibResults[i]);

    printf("Thread[%d] createdt", fibResults[i]); 

    fflush(stdout);

    pthread_join(thread, NULL);

    printf("Thread[%d] joined & exitedt", i); 

  }

  return 0;

}

Here is what happens when I compile:

gcc -o fibonacci fibonacci.c

fibonacci.c:17:15: error: array subscript is not an integer

    fibResults[arg] = 0;

              ^~~~

fibonacci.c:18:57: error: array subscript is not an integer

    printf("The fibonacci of %d= %dn", *arg, fibResults[*arg]);    

                                                        ^~~~~

fibonacci.c:22:16: warning: comparison between pointer and integer ('void *' and 'int')

  else if (arg == 1)

           ~~~ ^  ~

fibonacci.c:24:15: error: array subscript is not an integer

    fibResults[*arg] = 1;

              ^~~~~

fibonacci.c:25:57: error: array subscript is not an integer

    printf("The fibonacci of %d= %dn", *arg, fibResults[*arg]);   

                                                        ^~~~~

fibonacci.c:30:15: error: array subscript is not an integer

    fibResults[*arg] = fibResults[*arg -1] + fibResults[*arg -2];

              ^~~~~

fibonacci.c:30:40: error: invalid operands to binary expression ('void' and 'int')

    fibResults[*arg] = fibResults[*arg -1] + fibResults[*arg -2];

                                  ~~~~ ^~

fibonacci.c:30:62: error: invalid operands to binary expression ('void' and 'int')

    fibResults[*arg] = fibResults[*arg -1] + fibResults[*arg -2];

                                                        ~~~~ ^~

fibonacci.c:31:57: error: array subscript is not an integer

    printf("The fibonacci of %d= %dn", *arg, fibResults[*arg]);