/******************************************************** * An example source module to accompany... * * "Using POSIX Threads: Programming with Pthreads" *     by Brad nichols, Dick Buttlar, Jackie Farrell *     O'Reilly & Associates, Inc. * ******************************************************** * simple_processes.c * * Simple multi-process example. */#include <stdlib.h>#include <stdio.h>#include <unistd.h>#include <sys/types.h>#include <sys/ipc.h>#include <sys/shm.h>#include <sys/wait.h>#include <errno.h>  void do_one_thing(int *);void do_another_thing(int *);void do_wrap_up(int, int);int   shared_mem_id;int   *shared_mem_ptr;int   *r1p;int   *r2p;extern int main(void){  pid_t  child1_pid, child2_pid;  int  status;  /* initialize shared memory segment */  if ((shared_mem_id = shmget(IPC_PRIVATE, 2*sizeof(int), 0660)) == -1)    perror("shmget"), exit(1);  if ((shared_mem_ptr = (int *)shmat(shared_mem_id, (void *)0, 0)) == (void *)-1)    perror("shmat failed"), exit(1);  r1p = shared_mem_ptr;    r2p = (shared_mem_ptr + 1);  *r1p = 0;  *r2p = 0;  if ((child1_pid = fork()) == 0) {    /* first child */    do_one_thing(r1p);    return 0;  } else if (child1_pid == -1) {    perror("fork"), exit(1);  }  /* parent */  if ((child2_pid = fork()) == 0) {    /* second child */    do_another_thing(r2p);    return 0;  } else if (child2_pid == -1) {      perror("fork"), exit(1);  }  /* parent */  if ((waitpid(child1_pid, &status, 0) == -1))	perror("waitpid"), exit(1);  if ((waitpid(child2_pid, &status, 0) == -1))	perror("waitpid"), exit(1);  do_wrap_up(*r1p, *r2p);   return 0; }void do_one_thing(int *pnum_times){  int i, j, x;    for (i = 0;  i < 4; i++) {    printf("doing one thing\n");     for (j = 0; j < 10000; j++) x = x + i;    (*pnum_times)++;  }}void do_another_thing(int *pnum_times){  int i, j, x;    for (i = 0;  i < 4; i++) {    printf("doing another \n");     for (j = 0; j < 10000; j++) x = x + i;    (*pnum_times)++;  }}void do_wrap_up(int one_times, int another_times){  int total;  total = one_times + another_times;  printf("All done, one thing %d, another %d for a total of %d\n",	one_times, another_times, total);}