记录锁的特性

1.用F_GETLK调用fcntl，当调用进程是持有记录锁的进程时，F_GETLK命令不会报告调用进程自己持有的锁。
2.多次对文件加锁，那么按照加锁的最大范围计算，比如先加锁全部文件，再加锁一个文件的0-2字节，那么加锁的范围是全部文件。

进程1加记录锁
1>锁住1，2，3字节
2>锁住全部字节
进程2用F_GETLK获取记录锁情况（只锁定1>情况下）：
iret=0
+========child=======+
0-1 byte is unlock.
2-1 byte is WR lock.
2-2 byte is WR lock.
2-3 byte is WR lock.
3-1 byte is WR lock.
3-2 byte is WR lock.
4-1 byte is unlock.
5-1 byte is unlock.
6-1 byte is unlock.
7-1 byte is unlock.
8-1 byte is unlock.
9-1 byte is unlock.
10-1 byte is unlock.
+======parent========+
0-1 byte is unlock.
2-1 byte is unlock.
2-2 byte is unlock.
2-3 byte is unlock.
2-4 byte is unlock.
3-2 byte is unlock.
6-1 byte is unlock.

进程2用F_GETLK获取记录锁情况（1>,2>都执行情况下）：
iret=0
+========child=======+
0-1 byte is WR lock.
2-1 byte is WR lock.
2-2 byte is WR lock.
2-3 byte is WR lock.
3-1 byte is WR lock.
3-2 byte is WR lock.
4-1 byte is WR lock.
5-1 byte is WR lock.
6-1 byte is WR lock.
7-1 byte is WR lock.
8-1 byte is WR lock.
9-1 byte is WR lock.
10-1 byte is WR lock.
+======parent========+
0-1 byte is unlock.
2-1 byte is unlock.
2-2 byte is unlock.
2-3 byte is unlock.
2-4 byte is unlock.
3-2 byte is unlock.
6-1 byte is unlock.

#include <stdio.h>
#include <fcntl.h>
#include <sys/fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <errno.h>
#include <sys/wait.h>
#include <stdlib.h>


#define lockfullwrfile(fd) (lockfile(fd,F_WRLCK,0,0,SEEK_SET))
#define lockapartofwrfile(fd,start,len) (lockfile(fd,F_WRLCK,start,len,SEEK_SET))

int lockfile(int fd, int type , off_t start , off_t len , int whence) {

    struct flock l;

    l.l_pid = getpid();
    l.l_start = start;
    l.l_type = type;
    l.l_whence = whence;
    l.l_len = len;

    return fcntl(fd, F_SETLK,&l);
}
#define unlockfullfile(fd) (unlockfile(fd,F_WRLCK,0,0,SEEK_SET))
#define unlockapartoffile(fd,start,len) (unlockfile(fd,F_WRLCK,start,len,SEEK_SET))

int unlockfile(int fd, int type , off_t start , off_t len , int whence) {

    struct flock l;

    l.l_pid = getpid();
    l.l_start = start;
    l.l_type = type;
    l.l_whence = whence;
    l.l_len = len;

    return fcntl(fd, F_UNLCK,&l);
}

#define unlockfullfile(fd) (unlockfile(fd,F_WRLCK,0,0,SEEK_SET))
#define unlockapartoffile(fd,start,len) (unlockfile(fd,F_WRLCK,start,len,SEEK_SET))

int getlockfile(int fd, int type , off_t start , off_t len , int whence) {

    struct flock l;
    int ret = 0;
    l.l_pid = getpid();
    l.l_start = start;
    l.l_type = type;
    l.l_whence = whence;
    l.l_len = len;

    ret = fcntl(fd, F_GETLK,&l);
    if (ret < 0) {
        perror("GETLK error\n");
        return l.l_pid;
    }
    return l.l_type;
}

void printistype(int type,char * region){
    if (!region) {
        printf("region is empty.\n");
        return;
    }
    switch (type) {
        case F_WRLCK:
            printf("%s byte is WR lock.\n",region);
            break;
        case F_RDLCK:
            printf("%s byte is RD lock.\n",region);
            break;
        case F_UNLCK:
            printf("%s byte is unlock.\n",region);
            break;
        default:
            printf("%s byte is error.\n",region);
            break;
    }

}
/**
 * 测试：在同一个进程中对一个文件全体加锁，然后在对一个文件一部分加锁，看看文件哪个锁起作用
 * 结果：对全体加锁起作用，
 */
int main(){

    ssize_t ret = 0;
    int iret = 0 ;
    int fd = 0;
    pid_t pid = 0 , pret = 0;
    fd = open("/Users/panghongjiang/lock2file.txt",O_CREAT|O_RDWR, \
              S_IRUSR|S_IWUSR);

    if (fd < 0) {
        perror("fd error\n");
        return -1;
    }

    ret = write(fd, "abcdefg", 8);

    if (ret != 8) {
        perror("write is not full.\n");
        close(fd);
        return -1;
    }

    lockapartofwrfile(fd, 1, 3); //1>
    iret = lockfullwrfile(fd); //2>
    printf("iret=%d\n",iret);

    if ((pid = fork()) < 0) {
        printf("fork error\n");
    } else if (0 == pid) {
        if ((iret = getlockfile(fd,F_WRLCK,0,1,SEEK_SET) ) < 0)
            printf("getlockfile error\n");
        printistype(iret,"0-1");

        if ((iret = getlockfile(fd,F_WRLCK,2,1,SEEK_SET) ) < 0)
            printf("getlockfile error\n");
        printistype(iret,"2-1");

        if ((iret = getlockfile(fd,F_WRLCK,2,2,SEEK_SET) ) < 0)
            printf("getlockfile error\n");
        printistype(iret,"2-2");

        if ((iret = getlockfile(fd,F_WRLCK,2,3,SEEK_SET) ) < 0)
            printf("getlockfile error\n");
        printistype(iret,"2-3");


        if ((iret = getlockfile(fd,F_WRLCK,3,1,SEEK_SET) ) < 0)
            printf("getlockfile error\n");
        printistype(iret,"3-1");


        if ((iret = getlockfile(fd,F_WRLCK,3,2,SEEK_SET) ) < 0)
            printf("getlockfile error\n");
        printistype(iret,"3-2");


        if ((iret = getlockfile(fd,F_WRLCK,4,1,SEEK_SET) ) < 0)
            printf("getlockfile error\n");
        printistype(iret,"4-1");

        if ((iret = getlockfile(fd,F_WRLCK,5,1,SEEK_SET) ) < 0)
            printf("getlockfile error\n");
        printistype(iret,"5-1");

        if ((iret = getlockfile(fd,F_WRLCK,6,1,SEEK_SET) ) < 0)
            printf("getlockfile error\n");
        printistype(iret,"6-1");


        if ((iret = getlockfile(fd,F_WRLCK,7,1,SEEK_SET) ) < 0)
            printf("getlockfile error\n");
        printistype(iret,"7-1");


        if ((iret = getlockfile(fd,F_WRLCK,8,1,SEEK_SET) ) < 0)
            printf("getlockfile error\n");
        printistype(iret,"8-1");

        if ((iret = getlockfile(fd,F_WRLCK,9,1,SEEK_SET) ) < 0)
            printf("getlockfile error\n");
        printistype(iret,"9-1");

        if ((iret = getlockfile(fd,F_WRLCK,10,1,SEEK_SET) ) < 0)
            printf("getlockfile error\n");
        printistype(iret,"10-1");
        exit(0);
    }else {
        while ( pid != (pret = waitpid(pid, NULL, 0)));
    }


    if ((iret = getlockfile(fd,F_WRLCK,0,1,SEEK_SET) ) < 0)
        printf("getlockfile error\n");
    printistype(iret,"0-1");

    if ((iret = getlockfile(fd,F_WRLCK,2,1,SEEK_SET) ) < 0)
        printf("getlockfile error\n");
    printistype(iret,"2-1");

    if ((iret = getlockfile(fd,F_WRLCK,2,2,SEEK_SET) ) < 0)
        printf("getlockfile error\n");
    printistype(iret,"2-2");

    if ((iret = getlockfile(fd,F_WRLCK,2,3,SEEK_SET) ) < 0)
        printf("getlockfile error\n");
    printistype(iret,"2-3");


    if ((iret = getlockfile(fd,F_WRLCK,2,3,SEEK_SET) ) < 0)
        printf("getlockfile error\n");
    printistype(iret,"2-4");


    if ((iret = getlockfile(fd,F_WRLCK,3,2,SEEK_SET) ) < 0)
        printf("getlockfile error\n");
    printistype(iret,"3-2");


    if ((iret = getlockfile(fd,F_WRLCK,6,1,SEEK_SET) ) < 0)
        printf("getlockfile error\n");
    printistype(iret,"6-1");

    close(fd);

    return 0;
}