system V信號量操作類似於posix信號量,但system V信號量的操作要複雜得多,posix信號量使用步驟為sem_init(sem_open)-->sem_wait(sem_post) --> sem_close詳見上一節,system V使用不同的函數。
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
int semget(key_t key, int nsems, int semflg);
key為ftok返回值或IPC_PRIVATE; nsems為指定信號量集合中信號量的數量,一旦創建就不能更改,需要大於0,如果等於0則方位一個已存在的集合。 semflg為讀寫權限值組合。IPC_CREAT(創建新的信號量集合)或IPC_CREAT|IPC_EXCL(當將要創建的信號量集合已經存在時,再試圖創建將返回EEXIST)。其實IPC_CREAT和IPC_EXCL的組合和open函數的O_CREAT和O_EXCL組合類似。
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
int semctl(int semid, int semnum, int cmd, ...);
semid為信號量標識,函數semget的返回值。 semnum為信號在信號集合中的序號。 cmd為操作的命令:
GETVAL - 返回指定信號量當前值;
SETVAL - 設置指定信號量的值;
IPC_RMIN - 刪除信號量集合。
其餘命令詳見man手冊。
初始化一個system V信號量如下:
int sln_seminit(const char* filename, int initval)
{
int semid;
key_t keyid;
keyid = ftok(filename, 0);
if (keyid < 0) {
fprintf(stderr, "ftok: %s\n", strerror(errno));
return -1;
}
semid = semget(keyid, 1, IPC_CREAT | IPC_EXCL);
if (semid >=
0) { // 創建成功,然後修改信號量的初始值為initval
printf("=== new sem create! ===\n");
if (semctl(semid, 0, SETVAL, initval) < 0) {
printf("semctl: %s\n", strerror(errno));
return -1;
}
} else if (EEXIST ==
errno) { //信號量存在,則打開,再次修改信號量的初始值。
printf("=== open a exist sem! ===\n");
semid = semget(keyid, 0, 0);
if (semid < 0) {
printf("[%d] - semget: %s\n", __LINE__, strerror(errno));
return -1;
}
if (semctl(semid, 0, SETVAL, initval) < 0) {
printf("semctl: %s\n", strerror(errno));
return -1;
}
} else { //create failed, other reason
printf("[%d] - semget: %s, semid: %d\n", __LINE__, strerror(errno), semid);
}
return semid;
}
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
int semop(int semid, struct sembuf *sops, unsigned nsops);
int semtimedop(int semid, struct sembuf *sops, unsigned nsops, struct timespec *timeout); ```
semid為信號量標識,函數semget的返回值;<br>
sops指向信號量操作結構數組指針;<br>
nsops為指向數組中sembuf結構體個數。<br>
```c
struct sembuf {
short sem_num; // 要操作的信號量在信號量集裡的編號,
short sem_op; // 信號量操作
short sem_flg; // 操作表示符
};
若sem_op 是正數,其值就加到semval上,即釋放信號量控制的資源
若sem_op 是0,那麼調用者希望等到semval變為0,如果semval是0就返回;
若sem_op 是負數,那麼調用者希望等待semval變為大於或等於sem_op的絕對值
P、V操作的實現為:
void sln_sem_wait(int semid)
{
struct sembuf sb;
memset(&sb, 0, sizeof(struct sembuf));
sb.sem_num = SLN_SEM_NUM;
sb.sem_op = -1;
sb.sem_flg = 0;
if (semop(semid, &sb, 1) < 0) {
printf("shm lock error! semop: %s\n", strerror(errno));
}
}
void sln_sem_post(int semid)
{
struct sembuf sb;
sb.sem_num = SLN_SEM_NUM;
sb.sem_op = 1;
sb.sem_flg = 0;
//sb.sem_flg = SEM_UNDO;
if (semop(semid, &sb, 1) < 0) {
printf("shm unlock error! semop: %s\n", strerror(errno));
}
}
示例代碼: 服務進程:
#include <stdio.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/ipc.h> //ftok()
#include <string.h>
#include <sys/sem.h>
#include <sys/shm.h> //shmat()
#include <unistd.h> //access()
#include <stdlib.h> // exit()
#include <signal.h> //signal()
#include "shmipc.h"
int sem_clt2ser, sem_ser2clt, sem_mutex_id;
int sln_shm_get(const char* filename, void** mem, int mem_len)
{
int shmid;
key_t shm_key;
shm_key = ftok(filename, 0);
if (shm_key < 0) {
fprintf(stderr, "ftok: %s\n", strerror(errno));
return -1;
}
shmid = shmget(shm_key, mem_len, IPC_CREAT);
if (shmid < 0) {
printf("shmget: %s\n", strerror(errno));
return -1;
}
*mem = (void*)shmat(shmid, NULL, 0);
if ((void*) - 1 == *mem) {
printf("shmat: %s\n", strerror(errno));
return -1;
}
// semget(shm_key, 1, IPC_CREAT);
return shmid;
}
void sln_sem_wait_timeout(int semid)
{
struct sembuf sb;
struct timespec tp;
memset(&sb, 0, sizeof(struct sembuf));
sb.sem_num = SLN_SEM_NUM;
sb.sem_op = -1;
sb.sem_flg = 0;
tp.tv_sec = time(NULL) + SEM_TIMEOUT_SEC;
tp.tv_nsec = 0;
if (semtimedop(semid, &sb, 1, &tp) < 0) {
printf("shm lock error! semop: %s\n", strerror(errno));
}
}
void sln_sem_wait(int semid)
{
struct sembuf sb;
memset(&sb, 0, sizeof(struct sembuf));
sb.sem_num = SLN_SEM_NUM;
sb.sem_op = -1;
sb.sem_flg = 0;
if (semop(semid, &sb, 1) < 0) {
printf("shm lock error! semop: %s\n", strerror(errno));
}
}
void sln_sem_post(int semid)
{
struct sembuf sb;
sb.sem_num = SLN_SEM_NUM;
sb.sem_op = 1;
sb.sem_flg = 0;
//sb.sem_flg = SEM_UNDO;
if (semop(semid, &sb, 1) < 0) {
printf("shm unlock error! semop: %s\n", strerror(errno));
}
}
void sln_shm_lock(int semid)
{
struct sembuf sb;
memset(&sb, 0, sizeof(struct sembuf));
sb.sem_num = SLN_SEM_NUM;
sb.sem_op = -1;
//sb.sem_flg = 0;
sb.sem_flg = SEM_UNDO;
if (semop(semid, &sb, 1) < 0) {
printf("shm lock error! semop: %s\n", strerror(errno));
}
}
void sln_shm_unlock(int semid)
{
struct sembuf sb;
sb.sem_num = SLN_SEM_NUM;
sb.sem_op = 1;
//sb.sem_flg = 0;
sb.sem_flg = SEM_UNDO;
if (semop(semid, &sb, 1) < 0) {
printf("shm unlock error! semop: %s\n", strerror(errno));
}
}
int sln_seminit(const char* filename, int initval)
{
int semid;
key_t keyid;
keyid = ftok(filename, 0);
if (keyid < 0) {
fprintf(stderr, "ftok: %s\n", strerror(errno));
return -1;
}
semid = semget(keyid, 1, IPC_CREAT | IPC_EXCL);
if (semid >= 0) { // create success
printf("=== new sem create! ===\n");
if (semctl(semid, 0, SETVAL, initval) < 0) {
printf("semctl: %s\n", strerror(errno));
return -1;
}
} else if (EEXIST == errno) { //exist, create failed!
printf("=== open a exist sem! ===\n");
semid = semget(keyid, 0, 0);
if (semid < 0) {
printf("[%d] - semget: %s\n", __LINE__, strerror(errno));
return -1;
}
if (semctl(semid, 0, SETVAL, initval) < 0) {
printf("semctl: %s\n", strerror(errno));
return -1;
}
} else { //create failed, other reason
printf("[%d] - semget: %s, semid: %d\n", __LINE__, strerror(errno), semid);
}
return semid;
}
static void sln_create_not_exist_file(const char* filename)
{
FILE* fp = NULL;
if (access(filename, F_OK) < 0) {
fp = fopen(filename, "w+");
if (NULL == fp) {
fprintf(stderr, "fopen <%s> failed!\n", filename);
return;
}
fclose(fp);
}
}
static void sigint_func(int sig)
{
if (semctl(sem_clt2ser, 0, IPC_RMID) < 0) {
printf("semctl: %s\n", strerror(errno));
}
if (semctl(sem_ser2clt, 0, IPC_RMID) < 0) {
printf("semctl: %s\n", strerror(errno));
}
if (semctl(sem_mutex_id, 0, IPC_RMID) < 0) {
printf("semctl: %s\n", strerror(errno));
}
exit(0);
}
int main(int argc, const char* argv[])
{
char* str = NULL;
sln_create_not_exist_file(SLN_SEM_SERWAIT_FILEPATH);
sln_create_not_exist_file(SLN_SEM_CLTWAIT_FILEPATH);
sln_create_not_exist_file(SLN_SEM_MUTEX_FILEPATH);
sem_clt2ser = sln_seminit(SLN_SEM_SERWAIT_FILEPATH, 0);
if (sem_clt2ser < 0) {
printf("sync sem init failed!\n");
return -1;
}
sem_ser2clt = sln_seminit(SLN_SEM_CLTWAIT_FILEPATH, 0);
if (sem_clt2ser < 0) {
printf("sync sem init failed!\n");
return -1;
}
sem_mutex_id = sln_seminit(SLN_SEM_MUTEX_FILEPATH, 1);
if (sem_mutex_id < 0) {
printf("mutex sem init failed!\n");
return -1;
}
//signal(SIGINT, sigint_func);
for (;;) {
printf("--------start wait!---semval: %d------\n", semctl(sem_clt2ser, 0,
GETVAL, 0));
sln_sem_wait(sem_clt2ser);
printf("=====stat handle!========\n");
sln_shm_lock(sem_mutex_id);
sln_shm_get(SLN_SEM_MUTEX_FILEPATH, (void**)&str, 32);
sleep(6);
printf("str: %s\n", str);
if (shmdt(str) < 0) {
printf("shmdt: %s\n", strerror(errno));
}
sln_shm_unlock(sem_mutex_id);
printf("=====handle ok!========\n");
sln_sem_post(sem_ser2clt);
}
return 0;
}
客戶進程代碼:
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h> //ftok()
#include <sys/sem.h>
#include "shmipc.h"
int sln_shm_get(const char* filename, void** mem, int mem_len)
{
int shmid;
key_t shm_key;
shm_key = ftok(filename, 0);
if (shm_key < 0) {
fprintf(stderr, "ftok: %s\n", strerror(errno));
return -1;
}
shmid = shmget(shm_key, mem_len, IPC_CREAT);
if (shmid < 0) {
printf("shmget: %s\n", strerror(errno));
return -1;
}
*mem = (void*)shmat(shmid, NULL, 0);
if ((void*) - 1 == *mem) {
printf("shmat: %s\n", strerror(errno));
return -1;
}
return shmid;
}
void sln_sem_wait_timeout(int semid)
{
struct sembuf sb;
struct timespec tp;
memset(&sb, 0, sizeof(struct sembuf));
sb.sem_num = SLN_SEM_NUM;
sb.sem_op = -1;
sb.sem_flg = 0;
tp.tv_sec = time(NULL) + SEM_TIMEOUT_SEC;
tp.tv_nsec = 0;
/*
if (semtimedop(semid, &sb, 1, &tp) < 0) {
printf("shm lock error! semop: %s\n", strerror(errno));
}
*/
if (semop(semid, &sb, 1) < 0) {
printf("shm lock error! semop: %s\n", strerror(errno));
}
}
void sln_sem_wait(int semid)
{
struct sembuf sb;
memset(&sb, 0, sizeof(struct sembuf));
sb.sem_num = SLN_SEM_NUM;
sb.sem_op = -1;
sb.sem_flg = 0;
if (semop(semid, &sb, 1) < 0) {
printf("shm lock error! semop: %s\n", strerror(errno));
}
}
void sln_sem_post(int semid)
{
struct sembuf sb;
sb.sem_num = SLN_SEM_NUM;
sb.sem_op = 1;
sb.sem_flg = 0;
//sb.sem_flg = SEM_UNDO;
if (semop(semid, &sb, 1) < 0) {
printf("shm unlock error! semop: %s\n", strerror(errno));
}
}
void sln_shm_lock(int semid)
{
struct sembuf sb;
memset(&sb, 0, sizeof(struct sembuf));
sb.sem_num = SLN_SEM_NUM;
sb.sem_op = -1;
sb.sem_flg = 0;
if (semop(semid, &sb, 1) < 0) {
printf("shm lock error! semop: %s\n", strerror(errno));
}
}
void sln_shm_unlock(int semid)
{
struct sembuf sb;
sb.sem_num = SLN_SEM_NUM;
sb.sem_op = 1;
sb.sem_flg = 0;
if (semop(semid, &sb, 1) < 0) {
printf("shm unlock error! semop: %s\n", strerror(errno));
}
}
int sln_semget(const char* filename)
{
int semid;
key_t keyid;
keyid = ftok(filename, 0);
if (keyid < 0) {
fprintf(stderr, "ftok: %s\n", strerror(errno));
return -1;
}
return semget(keyid, 0, 0);
}
int main(int argc, const char* argv[])
{
char* str = NULL;
int sem_clt2ser, sem_ser2clt, sem_mutex_id;
sem_clt2ser = sln_semget(SLN_SEM_SERWAIT_FILEPATH);
if (sem_clt2ser < 0) {
printf("semget: %s\n", strerror(errno));
return -1;
}
sem_ser2clt = sln_semget(SLN_SEM_CLTWAIT_FILEPATH);
if (sem_ser2clt < 0) {
printf("semget: %s\n", strerror(errno));
return -1;
}
sem_mutex_id = sln_semget(SLN_SEM_MUTEX_FILEPATH);
if (sem_mutex_id < 0) {
printf("mutex sem failed!\n");
return -1;
}
printf("--------cli wait!-sem_mutex_id: %d--------\n", sem_mutex_id);
sln_shm_lock(sem_mutex_id);
printf("--------cli wait ok !---------\n");
sln_shm_get(SLN_SEM_MUTEX_FILEPATH, (void**)&str, 32);
strcpy(str, argv[1]);
sln_shm_unlock(sem_mutex_id);
sln_sem_post(sem_clt2ser);
sln_sem_wait(sem_ser2clt);
printf("=========set: %s=========\n", str);
return 0;
}
http://download.csdn.net/detail/gentleliu/8329425