一.低级通信--信号通信
signal.c
#include <signal.h>
#include <stdio.h>
#include <unistd.h>
/*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 <stdio.h>
#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 <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/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 <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/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 <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/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 <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/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 <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/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)
}
一、简介共享内存为在多个进程之间共享和传递数据提供了一种有效的方式。
但它本身并未提供同步机制。
在实际编程中，可以使用
信号量，
传递消息(使用管道或IPC消息)，
生成信号，
条件变量，
等方法来提供读写之间的有效的同步机制。
本例程序使用信号量进行同步，
主要是因为它方便，使用广泛，且独立于进程。
本例程序实现了，
生产者进程:
每次读取YUV输入文件的一帧，
然后将其写到共享内存中。
消费者进程:
每次从共享内存中读到一帧，
处理后，
将其写到输出文件。
两个进程间使用信号量来保证同步处理每一帧。
本例程序很好地示范了共享内存和信号量的机制，
对于实际程序的开发很有意义。
二、生产者进程
common.h
用来设置一些测试用的基本参数。
/*
* \File
* common.h
*/
#ifndef __COMMON_H__
#define __COMMON_H__
#define TEST_FILE "coastguard_cif.yuv"
#define OUTPUT_FILE "coastguard_cif_trsd.yuv"
#define FYUV_WIDTH 352
#define FYUV_HEIGHT 288
#endif
共享内存相关的头文件。
shm_com.h
/*
* \File
* shm_com.h
* \Brief
*/
#ifndef __SHM_COM_H__
#define __SHM_COM_H__
#define SHM_SEED 1001
#define MAX_SHM_SIZE 2048*2048*3
typedef struct shared_use_st
{
int end_flag //用来标记进程间的内存共享是否结束: 0, 未结束； 1， 结束
char shm_sp[MAX_SHM_SIZE]//共享内存的空间
}shared_use_st
#endif
信号量的头文件
semaphore.h
/*
* \File
* semaphore.h
* \Brief
* semaphore operation
*/
#ifndef __SEMAPHORE_H__
#define __SEMAPHORE_H__
#define SEM_SEED 1000
union semun
{
int val
struct semid_ds *buf
unsigned short *array
}
int set_semvalue(int sem_id, int value)
void del_semvalue(int sem_id)
int semaphore_p(int sem_id)
int semaphore_v(int sem_id)
#endif
帧处理的头文件
frame.h
/*
* \File
* frame.h
* \Brief
*
*/
#ifndef __FRAME_H__
#define __FRAME_H__
#include "shm_com.h"
#define PIX_VALUE 1
typedef enum
{
YUV420,
YUV422,
YUV444,
RGB
}frame_type_e
typedef struct
{
int frm_w// width
int frm_h// height
frame_type_e frm_type
int frm_size
char *frm_comps
}frame_t, *frame_p
int init_frame(frame_p frame, int width, int height, frame_type_e type)
int free_frame(frame_p frame)
int read_frame_from_file(frame_p frame, FILE* fp)
int write_frame_into_file(FILE* fp, frame_p frame)
int read_frame_from_shm(frame_p frame, shared_use_st* shm)
int write_frame_into_shm(shared_use_st* shm, frame_p frame)
int crop_frame(frame_p frame, int l_offset, int t_offset, int c_w, int c_h)
#endif
生产者进程的基本流程:
打开输入文件并初始化帧
创建并初始化共享内存和信号量
然后每次读取一帧，
用信号量获取共享内存的权限后，
将读取的帧写入共享内存，
再释放共享内存的权限。
当处理完所有的帧后，
设置结束标志，
并释放相关的资源。
producer.c
/*
* \File
* producer.c
* \Brief
* Test shared-memory and message-queue
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/shm.h>
#include <sys/sem.h>
#include "common.h"
#include "semaphore.h"
#include "shm_com.h"
#include "frame.h"
int main(char argc, char* argv[])
{
FILE* fp_in = NULL
frame_t frame
int frame_cnt = 0
int sem_id// semaphore id
int shm_id// shared-memory id
void* shared_memory = (void*)0
shared_use_st* shared_stuff
/* Open input file */
if ((fp_in = fopen(TEST_FILE, "rb")) <0 )
{
printf("Open input file failed: %s\n", TEST_FILE)
exit(EXIT_FAILURE)
}
/* Init frame */
init_frame(&frame, FYUV_WIDTH, FYUV_HEIGHT, YUV420)
printf("FRAME: w = %d, h = %d\n", frame.frm_w, frame.frm_h)
/* Create and init semaphore */
sem_id = semget((key_t)SEM_SEED, 1, 0666 | IPC_CREAT)
if (sem_id == -1)
{
fprintf(stderr, "semget failed.\n")
exit(EXIT_FAILURE)
}
/* Init shared-memory */
shm_id = shmget((key_t)SHM_SEED, sizeof(struct shared_use_st), 0666 | IPC_CREAT)
if (shm_id == -1)
{
fprintf(stderr, "shmget failed.\n")
exit(EXIT_FAILURE)
}
shared_memory = shmat(shm_id, (void*)0, 0)
if (shared_memory == (void*)-1)
{
fprintf(stderr, "shmat failed.\n")
exit(EXIT_FAILURE)
}
shared_stuff = (struct shared_use_st*)shared_memory
shared_stuff->end_flag = 0
printf("FRAME_CNT: %d\n", frame_cnt)
set_semvalue(sem_id, 1)
while (read_frame_from_file(&frame, fp_in) == 0)
{
semaphore_p(sem_id)
/* Write it into shared memory */
write_frame_into_shm(shared_stuff, &frame)
shared_stuff->end_flag = 0
semaphore_v(sem_id)
frame_cnt++
printf("FRAME_CNT: %d\n", frame_cnt)
}
semaphore_p(sem_id)
shared_stuff->end_flag = 1
semaphore_v(sem_id)
/* over */
printf("\nProducer over!\n")
fclose(fp_in)
free_frame(&frame)
del_semvalue(sem_id)
if (shmdt(shared_memory) == -1)
{
fprintf(stderr, "shmdt failed.\n")
exit(EXIT_FAILURE)
}
exit(EXIT_SUCCESS)
}
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