这么高的悬赏，实例放后面。信号量(sem),如同进程一样，线程也可以通过信号量来实现通信，虽然是轻量级的。信号量函数的名字都以"sem_"打头。线程使用的基本信号量函数有四个。
信号量初始化。int sem_init (sem_t *sem , int pshared, unsigned int value)
这是对由sem指定的信号量进行初始化，设置好它的共享选项(linux 只支持为0，即表示它是当前进程的局部信号量)，然后给它一个初始值VALUE。
等待信号量。给信号量减1，然后等待直到信号量的值大于0。
int sem_wait(sem_t *sem)
释放信号量。信号量值加1。并通知其他等待线程。
int sem_post(sem_t *sem)
销毁信号量。我们用完信号量后都它进行清理。归还占有的一切资源。
int sem_destroy(sem_t *sem) #include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>
#include <errno.h>
#define return_if_fail(p) if((p) == 0){printf ("[%s]:func error!/n", __func__)return}
typedef struct _PrivInfo
{
sem_t s1
sem_t s2
time_t end_time
}PrivInfo
static void info_init (PrivInfo* thiz)
static void info_destroy (PrivInfo* thiz)
static void* pthread_func_1 (PrivInfo* thiz)
static void* pthread_func_2 (PrivInfo* thiz)
int main (int argc, char** argv)
{
pthread_t pt_1 = 0
pthread_t pt_2 = 0
int ret = 0
PrivInfo* thiz = NULL
thiz = (PrivInfo* )malloc (sizeof (PrivInfo))
if (thiz == NULL)
{
printf ("[%s]: Failed to malloc priv./n")
return -1
}
info_init (thiz)
ret = pthread_create (&pt_1, NULL, (void*)pthread_func_1, thiz)
if (ret != 0)
{
perror ("pthread_1_create:")
}
ret = pthread_create (&pt_2, NULL, (void*)pthread_func_2, thiz)
if (ret != 0)
{
perror ("pthread_2_create:")
}
pthread_join (pt_1, NULL)
pthread_join (pt_2, NULL)
info_destroy (thiz)
return 0
}
static void info_init (PrivInfo* thiz)
{
return_if_fail (thiz != NULL)
thiz->end_time = time(NULL) + 10
sem_init (&thiz->s1, 0, 1)
sem_init (&thiz->s2, 0, 0)
return
}
static void info_destroy (PrivInfo* thiz)
{
return_if_fail (thiz != NULL)
sem_destroy (&thiz->s1)
sem_destroy (&thiz->s2)
free (thiz)
thiz = NULL
return
}
static void* pthread_func_1 (PrivInfo* thiz)
{
return_if_fail(thiz != NULL)
while (time(NULL) < thiz->end_time)
{
sem_wait (&thiz->s2)
printf ("pthread1: pthread1 get the lock./n")
sem_post (&thiz->s1)
printf ("pthread1: pthread1 unlock/n")
sleep (1)
}
return
}
static void* pthread_func_2 (PrivInfo* thiz)
{
return_if_fail (thiz != NULL)
while (time (NULL) < thiz->end_time)
{
sem_wait (&thiz->s1)
printf ("pthread2: pthread2 get the unlock./n")
sem_post (&thiz->s2)
printf ("pthread2: pthread2 unlock./n")
sleep (1)
}
return
}
一个是Posix实现，一个是System V实现使用的环境不一样
一般来讲SV的适用于进程同步，POSIX适用于线程同步
System V进程同步 api：semget/semop/semctl
POSIX 线程同步 api:sem_init/sem_destroy
不过POSIX貌似还会分为有名和无名信号量上面说的是无名信号量。
具体的还要看使用的环境。
linux中的进程通信分为三个部分：低级通信，管道通信和进程间通信IPC（inter process communication）。linux的低级通信主要用来传递进程的控制信号——文件锁和软中断信号机制。linux的进程间通信IPC有三个部分——①信号量，②共享内存和③消息队列。以下是我编写的linux进程通信的C语言实现代码。操作系统为redhat9.0，编辑器为vi，编译器采用gcc。下面所有实现代码均已经通过测试，运行无误。一.低级通信--信号通信
signal.c
#include
#include
#include
/*捕捉到信号sig之后，执行预先预定的动作函数*/
void sig_alarm(int sig)
{
printf("---the signal received is %d. /n", sig)
signal(SIGINT, SIG_DFL)//SIGINT终端中断信号，SIG_DFL：恢复默认行为，SIN_IGN：忽略信号
}
int main()
{
signal(SIGINT, sig_alarm)//捕捉终端中断信号
while(1)
{
printf("waiting here!/n")
sleep(1)
}
return 0
}
二.管道通信
pipe.c
#include
#define BUFFER_SIZE 30
int main()
{
int x
int fd[2]
char buf[BUFFER_SIZE]
char s[BUFFER_SIZE]
pipe(fd)//创建管道
while((x=fork())==-1)//创建管道失败时，进入循环
/*进入子进程，子进程向管道中写入一个字符串*/
if(x==0)
{
sprintf(buf,"This is an example of pipe!/n")
write(fd[1],buf,BUFFER_SIZE)
exit(0)
}
/*进入父进程，父进程从管道的另一端读出刚才写入的字符串*/
else
{
wait(0)//等待子进程结束
read(fd[0],s,BUFFER_SIZE)//读出字符串，并将其储存在char s[]中
printf("%s",s)//打印字符串
}
return 0
}
三.进程间通信——IPC
①信号量通信
sem.c
#include
#include
#include
#include types.h>
#include ipc.h>
#include sem.h>
/*联合体变量*/
union semun
{
int val//信号量初始值
struct semid_ds *buf
unsigned short int *array
struct seminfo *__buf
}
/*函数声明，信号量定义*/
static int set_semvalue(void)//设置信号量
static void del_semvalue(void)//删除信号量
static int semaphore_p(void)//执行P操作
static int semaphore_v(void)//执行V操作
static int sem_id//信号量标识符
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)//创建一个信号量,IPC_CREAT表示创建一个新的信号量
/*如果有参数，设置信号量，修改字符*/
if (argc >1)
{
if (!set_semvalue())
{
fprintf(stderr, "Failed to initialize semaphore/n")
exit(EXIT_FAILURE)
}
op_char = 'X'
sleep(5)
}
for(i = 0i <10i++)
{
/*执行P操作*/
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)
/*执行V操作*/
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()//删除信号量
}
exit(EXIT_SUCCESS)
}
/*设置信号量*/
static int set_semvalue(void)
{
union semun sem_union
sem_union.val = 1
if (semctl(sem_id, 0, SETVAL, sem_union) == -1)
return(0)
return(1)
}
/*删除信号量*/
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")
}
/*执行P操作*/
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)
}
/*执行V操作*/
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)
}
②消息队列通信
send.c
#include
#include
#include
#include
#include
#include types.h>
#include ipc.h>
#include msg.h>
#define MAX_TEXT 512
/*用于消息收发的结构体--my_msg_type：消息类型，some_text：消息正文*/
struct my_msg_st
{
long int my_msg_type
char some_text[MAX_TEXT]
}
int main()
{
int running = 1//程序运行标识符
struct my_msg_st some_data
int msgid//消息队列标识符
char buffer[BUFSIZ]
/*创建与接受者相同的消息队列*/
msgid = msgget((key_t)1234, 0666 | IPC_CREAT)
if (msgid == -1)
{
fprintf(stderr, "msgget failed with error: %d/n", errno)
exit(EXIT_FAILURE)
}
/*向消息队列中发送消息*/
while(running)
{
printf("Enter some text: ")
fgets(buffer, BUFSIZ, stdin)
some_data.my_msg_type = 1
strcpy(some_data.some_text, buffer)
if (msgsnd(msgid, (void *)&some_data, MAX_TEXT, 0) == -1)
{
fprintf(stderr, "msgsnd failed/n")
exit(EXIT_FAILURE)
}
if (strncmp(buffer, "end", 3) == 0)
{
running = 0
}
}
exit(EXIT_SUCCESS)
}
receive.c
#include
#include
#include
#include
#include
#include types.h>
#include ipc.h>
#include msg.h>
/*用于消息收发的结构体--my_msg_type：消息类型，some_text：消息正文*/
struct my_msg_st
{
long int my_msg_type
char some_text[BUFSIZ]
}
int main()
{
int running = 1//程序运行标识符
int msgid//消息队列标识符
struct my_msg_st some_data
long int msg_to_receive = 0//接收消息的类型--0表示msgid队列上的第一个消息
/*创建消息队列*/
msgid = msgget((key_t)1234, 0666 | IPC_CREAT)
if (msgid == -1)
{
fprintf(stderr, "msgget failed with error: %d/n", errno)
exit(EXIT_FAILURE)
}
/*接收消息*/
while(running)
{
if (msgrcv(msgid, (void *)&some_data, BUFSIZ,msg_to_receive, 0) == -1)
{
fprintf(stderr, "msgrcv failed with error: %d/n", errno)
exit(EXIT_FAILURE)
}
printf("You wrote: %s", some_data.some_text)
if (strncmp(some_data.some_text, "end", 3) == 0)
{
running = 0
}
}
/*删除消息队列*/
if (msgctl(msgid, IPC_RMID, 0) == -1)
{
fprintf(stderr, "msgctl(IPC_RMID) failed/n")
exit(EXIT_FAILURE)
}
exit(EXIT_SUCCESS)
}
③共享内存通信
share.h
#define TEXT_SZ 2048 //申请共享内存大小
struct shared_use_st
{
int written_by_you//written_by_you为1时表示有数据写入，为0时表示数据已经被消费者提走
char some_text[TEXT_SZ]
}
producer.c
#include
#include
#include
#include
#include types.h>
#include ipc.h>
#include shm.h>
#include "share.h"
int main()
{
int running = 1//程序运行标志位
void *shared_memory = (void *)0
struct shared_use_st *shared_stuff
char buffer[BUFSIZ]
int shmid//共享内存标识符
/*创建共享内存*/
shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666 | IPC_CREAT)
if (shmid == -1)
{
fprintf(stderr, "shmget failed/n")
exit(EXIT_FAILURE)
}
/*将共享内存连接到一个进程的地址空间中*/
shared_memory = shmat(shmid, (void *)0, 0)//指向共享内存第一个字节的指针
if (shared_memory == (void *)-1)
{
fprintf(stderr, "shmat failed/n")
exit(EXIT_FAILURE)
}
printf("Memory attached at %X/n", (int)shared_memory)
shared_stuff = (struct shared_use_st *)shared_memory
/*生产者写入数据*/
while(running)
{
while(shared_stuff->written_by_you == 1)
{
sleep(1)
printf("waiting for client.../n")
}
printf("Enter some text: ")
fgets(buffer, BUFSIZ, stdin)
strncpy(shared_stuff->some_text, buffer, TEXT_SZ)
shared_stuff->written_by_you = 1
if (strncmp(buffer, "end", 3) == 0)
{
running = 0
}
}
/*该函数用来将共享内存从当前进程中分离,仅使得当前进程不再能使用该共享内存*/
if (shmdt(shared_memory) == -1)
{
fprintf(stderr, "shmdt failed/n")
exit(EXIT_FAILURE)
}
printf("producer exit./n")
exit(EXIT_SUCCESS)
}
customer.c
#include
#include
#include
#include
#include types.h>
#include ipc.h>
#include shm.h>
#include "share.h"
int main()
{
int running = 1//程序运行标志位
void *shared_memory = (void *)0
struct shared_use_st *shared_stuff
int shmid//共享内存标识符
srand((unsigned int)getpid())
/*创建共享内存*/
shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666 | IPC_CREAT)
if (shmid == -1)
{
fprintf(stderr, "shmget failed/n")
exit(EXIT_FAILURE)
}
/*将共享内存连接到一个进程的地址空间中*/
shared_memory = shmat(shmid, (void *)0, 0)//指向共享内存第一个字节的指针
if (shared_memory == (void *)-1)
{
fprintf(stderr, "shmat failed/n")
exit(EXIT_FAILURE)
}
printf("Memory attached at %X/n", (int)shared_memory)
shared_stuff = (struct shared_use_st *)shared_memory
shared_stuff->written_by_you = 0
/*消费者读取数据*/
while(running)
{
if (shared_stuff->written_by_you)
{
printf("You wrote: %s", shared_stuff->some_text)
sleep( rand() % 4 )
shared_stuff->written_by_you = 0
if (strncmp(shared_stuff->some_text, "end", 3) == 0)
{
running = 0
}
}
}
/*该函数用来将共享内存从当前进程中分离,仅使得当前进程不再能使用该共享内存*/
if (shmdt(shared_memory) == -1)
{
fprintf(stderr, "shmdt failed/n")
exit(EXIT_FAILURE)
}
/*将共享内存删除,所有进程均不能再访问该共享内存*/
if (shmctl(shmid, IPC_RMID, 0) == -1)
{
fprintf(stderr, "shmctl(IPC_RMID) failed/n")
exit(EXIT_FAILURE)
}
exit(EXIT_SUCCESS)
}
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