lockf

lockf( fd, mode, size );

mode 为 1 时表示加锁，为 0 时表示解锁。

#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/wait.h>
#include<stdlib.h>

int main()
{
    pid_t pid;
    int retval;
    ] = "hello";
     )
    {
        printf("fork error\n");
        exit(-);
    }
     )
    {
        )
        {
            ,,) <  )
            {
                printf("lockf on error\n");
                exit(-);
            }
            sleep();
            printf("this is in child!\n");
            sleep();
            printf("this is in child!\n");

            ,,) < )
            {
                printf("lockf off error\n");
                exit(-);
            }
            sleep();
        }
        printf("this is child end\n");
        exit(-);
    }
    //wait(&retval);
    )
    {
        ,,) <  )
        {
            printf("lockf on error\n");
            exit(-);
        }
        sleep();
        printf("this is in parent!\n");
        sleep();
        printf("this is in parent!\n");

        ,,) < )
        {
            printf("lockf off error\n");
            exit(-);
        }
        sleep();
    }
    printf("this is parent process end\n");
    ;
}