c - Modify PID manager for multi-threading -

below pid manager. want modify uses multi-threading. therefore each thread request pid (maybe create 20 or in while loop), sleep random period of time (i assume use sleep() ), , release pid (similar see below).

i total newbie when comes threads in c , linux if can me modify accordingly. start clone() function call?

#include <stdio.h> #include <stdlib.h> #include <limits.h>  #define min_pid 300 #define max_pid 5000 #define cb char_bit  int sz = max_pid - min_pid + 1;  unsigned char *unsignedchar;  int allocate_map(); int allocate_pid(); void release_pid(int pid);  int main()  {     int map = allocate_map();     if (map == 1) {         printf("\nbitmap data structure initialized.\n");         int id = 0, = 0;      //create 20 processes         while (i < 20) {             int val = allocate_pid();             printf("\nprocess %d: pid = %d", i+1, val);             i++;         }     //release few processes     release_pid(303); printf("\nprocess 303 released.");     release_pid(308); printf("\nprocess 308 released.");     release_pid(309); printf("\nprocess 309 released.");      //allocate few more processes after release         int val = allocate_pid(); printf("\nprocess %d : pid = %d", ++i, val); //should 303     val = allocate_pid(); printf("\nprocess %d : pid = %d\n", ++i, val); //should 308     }     else printf("\nfailed initialize data structure.\n"); }  /* creates , initializes bitmap data structure representing pids;  returns —1 unsuccessful, 1 successful */ int allocate_map() {     unsignedchar = (unsigned char*)malloc((sz+cb-1)/cb * sizeof(char));     if (unsignedchar) return 1;     return -1; }  /* allocates , returns pid; returns -1 if unable allocate pid (all pids in use) */ int allocate_pid() {     int = 0;     int pid = unsignedchar[i/cb] & (1 << (i & (cb-1)));     while (pid != 0) {         i++;         pid = unsignedchar[i/cb] & (1 << (i & (cb-1)));         }      if (i+min_pid > max_pid) return -1;     unsignedchar[i/cb] |= 1 << (i & (cb-1));     return i+min_pid; }  /* releases pid given pid parameter*/ void release_pid(int pid) {     if (pid < 300) {         printf("\ninvalid pid: should lie between 300 , 3000.");         return;     }     int = pid - min_pid;     unsignedchar[i/cb] &= ~(1 << (i & (cb-1))); } 

posix threads simplest , canonical way this.

wikipedia has got nice example already.

basically, create thread instances means of pthread_create() , join them thereafter or "wait them finish" via pthread_join().

note wikipedia entry says compilation using gcc. -pthread or -lpthread strictly necessary there, otherwise you'll undefined references.