#include <linux/sem.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <stdlib.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <signal.h>

int start =  0 ;

#define LEN  20 

pid_t chpid [ 2 ];

int main (int argc, char *argv [])
{
    struct timeval c_time;
    void c_action (int);
    static struct sigaction pact, cact;
    char str [LEN];
    id_t pid;


     shm_unlink("myshered.shm");

     int fd_shm;
      
     if((fd_shm = shm_open("myshered.shm", O_RDWR|O_CREAT,  0777 )) <  0 )
     {perror ("error create shm");   return( 1 );}


    // создаем семафор
    int j,n,i= 0 ;


    int semid = semget(IPC_PRIVATE,  4 ,  0666  | IPC_CREAT );
    if (semid <  0 ){
        perror("semget");
            return  1 ;}

    struct sembuf s_red[ 2 ] = { 0 , - 1 , IPC_NOWAIT,  1 ,  1 , IPC_NOWAIT};
    struct sembuf s_green[ 2 ] = { 0 ,  1 , IPC_NOWAIT,  1 , - 1 , IPC_NOWAIT}; 
    struct sembuf s_wait[ 2 ] = { 0 ,  0 ,  0 ,  1 ,  0 ,  0 }; 
    struct sembuf s_readed = { 2 ,  0 ,  0 }; 
    struct sembuf s_lock = { 2 ,  1 , IPC_NOWAIT}; 
    struct sembuf s_unlock = { 2 , - 1 , IPC_NOWAIT}; 

    union semun arg;

    arg.val =  0 ;
    semctl(semid,  0 , SETVAL, arg);
    arg.val =  1 ;
    semctl(semid,  1 , SETVAL, arg);
    arg.val =  0 ;
    semctl(semid,  2 , SETVAL, arg);


    // создаем два процесса
    for (j= 0 ; j< 2 ; j++) {
    switch (chpid [j] = fork ()) {
    case - 1 :
        printf ("Fork call error\n");
        return  1 ;
    case  0 :
        //child
        cact.sa_flags = SA_SIGINFO;
        cact.sa_sigaction = (void *) c_action;
            sigaction (SIGUSR1, &cact, NULL);
        printf("child #%d\n",getpid());
        while (i <=  1000 ) {
          // ожидаем разрешения
           
            if ((start)&&
            (semop( semid, &s_readed,  1 )== 0 )&&
            (semop( semid, &s_wait[j],  1 )== 0 ))
            { 
            lseek (fd_shm,  0 , SEEK_END);
            i = semctl(semid,  3 , GETVAL);
            if (i== 1000 )break;
            for (n= 0 ;n< 100 ;n++){            
                gettimeofday(&c_time,NULL);
                sprintf (str,"%4d #%5d :%6d\n", i+n+ 1 , 
                    getpid (), c_time.tv_usec);
                write(fd_shm,str,LEN);
            }
            i+=n;
                arg.val = i;
                semctl(semid,  3 , SETVAL, arg);
            // переключаем поток
            if (j== 0 ) semop( semid, &s_green,  2 );
            else semop( semid, &s_red,  2 );  

            }
        }       
        return  0 ;
    }
    }
    printf("father #%d\n",getpid());
    //father
    kill (chpid [ 0 ], SIGUSR1);
    kill (chpid [ 1 ], SIGUSR1);
    i= 0 ;
        while (i <  1000 ) {
            sleep( 1 );
            // ожидаем разрешения
            j=semctl(semid,  3 , GETVAL);
            if( (j>i+ 75 )||(j== 1000 ))
            {
            // блокируем
                semop( semid, &s_lock,  1 );      
            // читаем   
            lseek (fd_shm, i*LEN, SEEK_SET);

            for (n= 0 ;n< 75 ;n++){
                if (i+n == 1000 ) break;
                read(fd_shm,str,LEN);
                printf ("%s", str);         
            }
                i+=n; 
            // разблокируем 
                semop( semid, &s_unlock,  1 );
            }           
        }
    /*close(fd);*/

    shm_unlink("myshered.shm");
    semctl(semid,  0 , IPC_RMID);
    return  0 ;
}

void c_action (int sig)
    {
      start =  1 ;
      printf("action #%d\n",getpid());
    }

 lseek (fd_shm, i*LEN, SEEK_SET);

read(fd_shm,str,LEN);

    kill (chpid [ 0 ], SIGUSR1);
    kill (chpid [ 1 ], SIGUSR1);