linux下 如何判断信号量延时

/*编译命令：gcc -o shm shm.c -g */

2

3#include<sys/sem.h>

4#include<sys/ipc.h>

5

6#define SEGSIZE 1024

7#define READTIME 1

8

9union semum

10{

11int val

12struct semid_ds *buf

13unsigned short *array

14}arg

15

16/* 创建信号量 */

17int sem_creat(key_t key)

18{

19union semun sem

20int semid

21sem.val = 0

22semid = semget(key, 1, IPC_CREAT | 0666)

23

24if (semid == -1)

25{

26printf("Create semaphore error\n")

27exit(-1)

28}

29

30semctl(semid, 0, SETVAL, sem)

31

32return semid

33}

34

35/* 删除信号量*/

36int del_sem(int semid)

37{

38union semun sem

39sem.val = 0

40semctl(semid, 0, IPC_RMID, sem)

41}

42

43/* 信号量的P操作，使得信号量的值加1 */

44int p(int semid)

45{

46struct sembuf sops = {0,

47 +1,

48 IPC_NOWAIT

49 }

50

51return (semop(semid, &sops, 1))

52}

53

54/* 信号量的v操作，使得信号量的值减1 */

55int v(int semid)

56{

57struct sembuf sops = {0,

58 -1,

59 IPC_NOWAIT

60 }

61

62return (semop(semid, &sops, 1))

63}

64

65/* server主程序 */

66int main(int argc, char **argv)

67{

68key_tkey

69int shmid, semid

70char *shm

71char msg[7] = "-data-"

72char i

73struct semid_ds buf

74

75key = ftok("/", 0)

76shmid = shmget(key, SEGSIZE, IPC_CREAT|0604)

77

78if shmid == -1)

79{

80printf(" create shared memory error\n")

81return -1

82}

83

84shm = (char *)shmat(shmid, 0, 0)

85if (-1 == (int)shm)

86{

87printf(" attach shared memory error\n")

88return -1

89}

90

91semid = sem_creat(key)

92

93for (i = 0i <= 3i++)

94{

95sleep(1)

96p(semid)

97sleep(READTIME)

98msg[5] = '0' + i

99memcpy(shm,msg,sizeof(msg))

100sleep(58)

101v(semid)

102}

103

104shmdt(shm)

105

106shmctl(shmid,IPC_RMID,&buf)

107

108del_sem(semid)

109

110return 0

111

112}

113

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完整程序要花不少时间调试的，我这里给你一个实现PV操作的程序吧，5个人抢3个位子，这个你们上课应该会讲的，通过几个pv操作就可以实现，只要把我这里写的pv操作的代码用上就可以了。程序是在linux系统下调试的。pv操作分别对应下面的up和down（我们老师习惯用这种称呼，于是就在代码中也这么用了）

#include <stdio.h>#include <signal.h>#include <unistd.h>#include <sys/types.h>#include <sys/stat.h>#include <sys/mman.h>#include <sys/times.h>#include <fcntl.h>#include <stdlib.h>#include <sys/sem.h> //include header file for semaphore #define FILE_SIZE 11#define NO_PROC 10 int DelayCount = 0int readerID = 0int writerID = 0char* shared_bufferint Delay100ms = 0int* shared_buffer2////////Variables for semaphoreoperations/////int semid// the followings are not necessary to definehere, but just for conveniencekey_t semkeystruct sembuf operation[1]short sarray[2]int ret_val/////////////////////////////////////////////// void init_sem(){ int*rc //getkey semkey=ftok("/dev/null",12)if( semkey == (key_t) -1 ) { printf("main:ftok() failed\n") exit(-1)} printf("semkeygenerated\n") //getsemaphore set semid= semget( semkey, 2, 0666 | IPC_CREAT | IPC_EXCL )if( semid == -1 ) { printf("main: semget()failed\n")exit(-1)} //setthe two semaphores to 1sarray[0]=1sarray[1]=1 ret_val=semctl(semid,1, SETALL, sarray)if(ret_val==-1) { printf("main:semctlerror\n") exit(-1)} printf("ddddd\n") //setreader count rc=(int*)(&shared_buffer[FILE_SIZE])//printf("%d\n",*shared_buffer2)*rc=0printf("RC:%d\n",*rc)} void down(int i) //i=0, 1{ operation[0].sem_num=ioperation[0].sem_op=-1operation[0].sem_flg=0ret_val=semop(semid,operation,1)} void up(int i){ operation[0].sem_num=ioperation[0].sem_op=1operation[0].sem_flg=0ret_val=semop(semid,operation,1)}

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