c - program spinning on pthread lock -

after banging head against wall few hours during exercise, stuck @ wall. first off, program designed find , print prime numbers between 1 , ceiling, ceiling user input. design implement posix threads.

in program, runs until on 1 of later iterations in thread's method. when gets later iteration, steps line pthread_mutex_lock(lock); , spins, forcing me kill ctrl+z. 2 input's i've been using 1 number of threads , 10 ceiling. flaw reproducible happens every time i've tried it. note: although code should able implement multiple threads, i'd working correctly 1 child thread before adding more.

#include <stdio.h> #include <stdlib.h> #include <pthread.h>  int* numbermarker = null; int* buffer = null; int* checked = null; int pullposition = 0; int placeposition = 0; pthread_mutex_t* lock; int ceiling;  /*this method places 1 of primes in buffer.  offers safe way manage next value placed*/ void placevalue(int value){     buffer[placeposition] = value;     placeposition++; }   void* threadmethod(){        int i;     int k;     int l;     while(1){            printf("pull %d   number %d \n",pullposition, buffer[pullposition]);         pthread_mutex_lock(lock);         printf("flag\n");         l = buffer[pullposition];         pullposition++;         printf("pulltwo %d   number %d \n",pullposition, buffer[pullposition-1]);         pthread_mutex_unlock(lock);         for(k=l+1;k<=ceiling;k++){             if(k%l){                 if(k%2){                     checked[k]=1;                     placevalue(k);                 }             }             else{                 numbermarker[k-1] = 1;             }         }         int sum=0;         for(i=0; i<ceiling; i++){             if(numbermarker[i]){                 checked[i] = numbermarker[i];             }             printf("checked|%d|%d|%d|%d|%d|%d|%d|%d|%d|%d|\n", checked[0], checked[1], checked[2], checked[3], checked[4], checked[5], checked[6], checked[7], checked[8], checked[9]);              sum += checked[i];             printf("sum %d    ceiling %d\n",sum,ceiling);         }         printf("number |%d|%d|%d|%d|%d|%d|%d|%d|%d|%d|\n", numbermarker[0],    numbermarker[1],    numbermarker[2],    numbermarker[3],    numbermarker[4],    numbermarker[5],    numbermarker[6],    numbermarker[7],    numbermarker[8],    numbermarker[9]);         if(sum == ceiling){             return null;         }     } }   int main() {     int numthreads;     int i;      printf("enter number of threads: \n");     scanf("%d", &numthreads);      printf("enter highest value check \n");     scanf("%d", &ceiling);      /*  hold 1's , 0's.             1 = number has been checked or                     confirmed not prime             0 = number possible prime              idea behind these values next             prime can identified 0             lowest index     */      numbermarker = (int*)malloc(sizeof(int)*(ceiling));     checked = (int*)malloc(sizeof(int)*(ceiling));      /*this hold primes found*/     buffer = (int*)malloc(sizeof(int)*(ceiling));      /*allocate space lock*/     lock = (pthread_mutex_t *) malloc(sizeof(pthread_mutex_t));     pthread_mutex_init(lock,null);      for(i=0; i<ceiling; i++){         if(i<1){             numbermarker[i] = 1;         }         else{             numbermarker[i] = 0;         }         checked[i]=0;         buffer[i]=0;         printf("%d \n",numbermarker[i]);     }     checked[0]=1;     placevalue(2);     printf("checked|%d|%d|%d|%d|%d|%d|%d|%d|%d|%d|\n", checked[0], checked[1], checked[2], checked[3], checked[4], checked[5], checked[6], checked[7], checked[8], checked[9]);      pthread_t **tid = (pthread_t **) malloc(sizeof(pthread_t *) * numthreads);      for(i=0;i<numthreads;i++){         tid[i] = (pthread_t *) malloc(sizeof(pthread_t));     }      for(i=0;i<numthreads;i++){         if(pthread_create(tid[i],                                             null,                                             threadmethod,                                             null)){             printf("could not create thread \n");             exit(-1);         }     }             for(i=0;i<numthreads;i++){         if(pthread_join(*tid[i], null)){             printf("error joining thread \n");             exit(-1);         }         free(tid[i]);     }      free(tid);     for(i=0;i<ceiling;i++){         if(numbermarker[i] == 0){             printf("%d sdfsddd \n", numbermarker[i]);             printf("%d \n", i+1);         }     }      free(buffer);     free(numbermarker);     buffer=null;     numbermarker=null;     return(0); } 

i've tried code , in

void placevalue(int value) { buffer[placeposition] = value; placeposition++; } 

placeposition goes beyond size of buffer. results in undefined behaviour, plausible outcome of trashing of mutex (which malloc()ed right after buffer).

on top of that, there's race condition placevalue(). however, if you're using single worker thread, not (yet) running it.