vim-------------------
im中翻页的命令
整页翻页 ctrl-f ctrl-b
f就是forword b就是backward
翻半页
ctrl-d ctlr-u
d=down u=up
滚一行
ctrl-e ctrl-y
zz 让光标所杂的行居屏幕中央
zt 让光标所杂的行居屏幕最上一行 t=top
zb 让光标所杂的行居屏幕最下一行 b=bottom
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/* After the #includes, the function prototypes and the global variable, we come to the
main function. There the semaphore is created with a call to semget, which returns the
semaphore ID. If the program is the first to be called (i.e. it's called with a parameter
and argc > 1), a call is made to set_semvalue to initialize the semaphore and op_char is
set to X. */
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/sem.h>
#include "semun.h"
static int set_semvalue(void); //给信号赋值，设置属性等
static void del_semvalue(void);
static int semaphore_p(void);
static int semaphore_v(void);
static int sem_id;
int main(int argc, char *argv[])
{
int i;
int pause_time;
char op_char = 'O';
srand((unsigned int)getpid());
sem_id = semget((key_t)1234, 1, 0666 | IPC_CREAT); //初始化信号量（相当于open）
if (argc > 1) //是起始程序
{
if (!set_semvalue()) {
fprintf(stderr, "Failed to initialize semaphore\n");
exit(EXIT_FAILURE);
}
op_char = 'X';
sleep(2);
}
/* Then we have a loop which enters and leaves the critical section ten times.
There, we first make a call to semaphore_p which sets the semaphore to wait, as
this program is about to enter the critical section. */
for(i = 0; i < 10; i++) {
if (!semaphore_p())
exit(EXIT_FAILURE);
printf("%c", op_char);fflush(stdout);
pause_time = rand() % 3;
sleep(pause_time);
printf("%c", op_char);fflush(stdout);
/* After the critical section, we call semaphore_v, setting the semaphore available,
before going through the for loop again after a random wait. After the loop, the call
to del_semvalue is made to clean up the code. */
if (!semaphore_v())
exit(EXIT_FAILURE);
pause_time = rand() % 2;
sleep(pause_time);
}
printf("\n%d - finished\n", getpid());
if (argc > 1) {
sleep(10);
del_semvalue();
}
exit(EXIT_SUCCESS);
}
/* The function set_semvalue initializes the semaphore using the SETVAL command in a
semctl call. We need to do this before we can use the semaphore. */
//给信号量赋初值
static int set_semvalue(void)
{
union semun sem_union;
sem_union.val = 1;
if (semctl(sem_id, 0, SETVAL, sem_union) == -1) //semctl()的二参是下标
return(0);
return(1);
}
/* The del_semvalue function has almost the same form, except the call to semctl uses
the command IPC_RMID to remove the semaphore's ID. */
//销毁信号量
static void del_semvalue(void)
{
union semun sem_union;
if (semctl(sem_id, 0, IPC_RMID, sem_union) == -1)
fprintf(stderr, "Failed to delete semaphore\n");
}
/* semaphore_p changes the semaphore by -1 (waiting). */
static int semaphore_p(void)
{
struct sembuf sem_b;
sem_b.sem_num = 0;
sem_b.sem_op = -1; /* P() */
sem_b.sem_flg = SEM_UNDO;
if (semop(sem_id, &sem_b, 1) == -1) {
fprintf(stderr, "semaphore_p failed\n");
return(0);
}
return(1);
}
/* semaphore_v is similar except for setting the sem_op part of the sembuf structure to 1,
so that the semaphore becomes available. */
static int semaphore_v(void)
{
struct sembuf sem_b;
sem_b.sem_num = 0;
sem_b.sem_op = 1; /* V() */
sem_b.sem_flg = SEM_UNDO;
if (semop(sem_id, &sem_b, 1) == -1) {
fprintf(stderr, "semaphore_v failed\n");
return(0);
}
return(1);
}
root@ubuntu:~/test/SourceCode/ch14# cat semun.h
#if defined(__GNU_LIBRARY__) && !defined(_SEM_SEMUN_UNDEFINED)
/* union semun is defined by including <sys/sem.h> */
#else
/* according to X/OPEN we have to define it ourselves */
union semun {
int val; /* value for SETVAL */
struct semid_ds *buf; /* buffer for IPC_STAT, IPC_SET */
unsigned short int *array; /* array for GETALL, SETALL */
struct seminfo *__buf; /* buffer for IPC_INFO */
};
#endif
先执行
stty -tostop
这个是确保产生的tty的输出的后台程序不会引发系统生成的一个信号
再
./sem1 1 &
./sem1
打印结果就是
root@ubuntu:~/test/SourceCode/ch14# ./sem1 1& [1] 14437 root@ubuntu:~/test/SourceCode/ch14# ./sem1 OOXXOOXXOOXXOOXXOOXXXXOOXXOOXXOOXXOOXX 14437 - finished OO 14438 - finished root@ubuntu:~/test/SourceCode/ch14#
发现了没？XX和OO都是成对出现的
信号量就是一个全局的锁，在多进程并行的时候，保持数据一致性的一个东西哦