簡述進程間通信方式

???? 進程間通信方式通常有共享內存 信號量 消息隊列 管道 FIFO Socket等幾種。??

???? 共享內存的模型，它是最有效率的進程間通信方式

???? 進程間信號量是進程間同步主要方式，信號量操作為負的時候，進程阻塞。直到信號量為正???

???? 內存映射是一種特殊的共享內存方式，只是本質上是對文件的操作

???? 管道是親戚進程間通信的常用方式，常用于輸入輸出重定向???

???? Fifo也成為命名管道，可用于無關聯進程之間

???? Socket是唯一一個不同主機間進程通信的方式

下面簡單介紹一下他們的特點與功能

????????????? 共享內存（分配 綁定 脫離 釋放）

1：效率高，特別是大數據量通信

2：各進程需要協調共同的鍵值，需要提供額外機制防止競爭條件

3：異步通信

4：和信號量一同使用

?????????????????? 內存映射(多進程共享文件進行通信的機制)

?????????????????? 1：分配內存

???????????????????2：讀入文件內容至內存

?????????????????? 3：內存的內容回寫到文件

????????????? 信號量

1：線程信號量:同步多線程環境的計數器。

2：進程間同步的信號量: System V信號量，操作和sharedmemory類似。

????????????? 消息隊列

1打開或創建消息隊列

2讀寫操作

3獲得或設置隊列屬性

????????????? 管道

1：單向信息的傳遞設備

2：用于進程的線程之間或者是父子進程之間通信

3：自動同步進程(管道的容量是有限的當管道寫滿的時候，寫入端自動阻塞管道容量4096字節)

?

????????????? FIFO

1：在文件系統中是一個有名字的管道

2：任何進程都可以打開

3：進程間無需關聯

?

????????????? SocketSocket

1：是一種雙向通信設備

2：同一主機不同進程間通信

3：不同主機間的通信

????以下是一些程序，幫助大家理解

?共享內存

#include"stdio.h"

????? #include"sys/shm.h"

????? #include"string.h"

????? #include"fcntl.h"

????? #include"sys/stat.h"

????? int main()

????? {

????????? pid_t pid;

??????? ??int share_id;

????????? share_id=shmget(IPC_PRIVATE,getpagesize(),IPC_CREAT | IPC_EXCL | S_IRUSR | S_IWUSR );

????????? pid=fork();

????????? if(pid==0)

????????? {

?????????????? char *share1=NULL;

?????????????? share1=(char*) shmat (share_id, 0,0);

? ?????????????memset(share1,0,getpagesize());

?????????????? strcpy(share1,"hello,everyone\n");

?????????????? shmdt(share1);

????????? }

????????? else if(pid>0)

????????? {

??????????????? char *share2=NULL;

??????????????? share2=(char*) shmat(share_id,0,0);

??????????????? printf("read characters from memory!\n");

??????????????? printf("%s\n",share2);

??????????????? shmdt(share2);

??????????????? shmctl(share_id,IPC_RMID,0);

????????? }

????????? ?return 1;

????? }

信號量

???? #include <sys/types.h>

???? #include <sys/ipc.h>

???? #include <sys/sem.h>

???? #include<stdio.h>

???? #include<sys/stat.h>

???? #include<fcntl.h>

???? #include<unistd.h>

???? #define MAX 3

???? union semun

??? {

??????? int val;

??????? struct semid_ds *buf;

??????? unsigned short int *array;

??????? struct seminfo *_buf;

??? };

??? int sig_alloc(key_t key, int sem_flags)

??? {

??????? return semget (key, MAX, sem_flags);

??? }

?

??? int sig_destory (int semid,int numth)

??? {

??????? union semun ignored_argument;

??????? return semctl (semid, numth, IPC_RMID,ignored_argument);

??? }

/*

??????? parray is a set of initialized value

*/

??? int sig_init (int semid,int *parray)

?? {

??????? union semun argument;

??????? int i=0;

??????? for(i=0;i<MAX;i++)

??????? {

??? ????//????? values[i] = *(parray+i);??

??????????????? argument.array = parray;

??????????????? semctl (semid, i, SETALL, argument);

??????? }

?? }

?? int sig_wait(int semid,int numth)

?? {

??????? struct sembuf operations[MAX];

??????? operations[numth-1].sem_num = numth-1;

??????? operations[numth-1].sem_op = -1;

??????? operations[numth-1].sem_flg = SEM_UNDO;

??????? return semop(semid,operations,1);

?? }

?

?int sig_post(int semid,int numth)

?? {

??????? struct sembuf operations[MAX];

??????? operations[numth-1].sem_num = numth-1;

??????? operations[numth-1].sem_op = 1;

??????? operations[numth-1].sem_flg = SEM_UNDO;

??????? return semop(semid,operations,1);

?? }

int main()

?? {

??????? pid_t pid;

??????? int sig_id,i=0;

??????? int sig_val[MAX]={1,0,0};

??????? sig_id=sig_alloc(0,IPC_CREAT);

??????? sig_init(sig_id,sig_val);

??????? pid=fork();

??????? if(pid==0)

??????? {

??????????????? while(++i<10)

??????????????? {

??????????????????????? sig_wait(sig_id,3);

??????????????????????? printf("*************** \n");

??????????????????????? sig_post(sig_id,3);

??????????????? }

??????? }

else if(pid)

??????? {

??????????????? i=0;

??????????????? while(++i<10)

??????????????? {

??????????????????????? sig_wait(sig_id,1);

??????????????????????? printf("++++++++++++++++\n");

??????????????????????? sig_post(sig_id,1);

??????????????? }

?

? ??????}

??????? return 1;

??? }

內存映射

#include <sys/mman.h>

#include <sys/types.h>

#include<stdio.h>

#include<string.h>

#include<sys/stat.h>

#include<stdlib.h>

#include<fcntl.h>

#include<unistd.h>

#define FILE_LENGTH 100

int main(int argc,char **argv)

{

??????? int fd1,fd2;

??????? char *pfile=NULL;

??????? char *load=NULL;

??????? int num;

??????? if(argc<3)

??????? {

??????????????? printf("please input more file\n");

??????????????? return 0;

??????? }

?

??????? fd1=open(argv[1],O_RDONLY);

??????? fd2=open(argv[2],O_RDWR|O_CREAT,S_IRUSR|S_IWUSR);

??????? printf("fd2=%d\n",fd2);

?

??????? //fd2=open(argv[2],O_WRONLY);

??????? lseek (fd2, FILE_LENGTH+1, SEEK_SET);

??????? write (fd2, "", 1);

??????? lseek (fd2, 0, SEEK_SET);

??????? printf("num=%d\n",num);

??????? printf("fd2=%d\n",fd2);

?

??????? pfile=(char*)mmap(0,FILE_LENGTH,PROT_WRITE|PROT_READ,MAP_PRIVATE,fd2,0);

??????? read(fd1,pfile,FILE_LENGTH);

??????? write(fd2,pfile,FILE_LENGTH);

??????? close(fd2);

??????? printf("pfile=%d\n",pfile);

??????? munmap(pfile,FILE_LENGTH);

??????? close(fd1);

??????? return 1;

}

? 管道

???? #include <sys/mman.h>

???? #include <sys/types.h>

???? #include<stdio.h>

???? #include<string.h>

???? #include<sys/stat.h>

???? #include<stdlib.h>

???? #include<fcntl.h>

???? #include<unistd.h>

?? int main ()

?? {

??? int fds[2];

??? pid_t pid;

??? pipe (fds);

??? pid = fork ();

??? if (pid == (pid_t) 0)

??? {

????? char str[10000];

????? sleep(1);

????? close(fds[1]);

????? read(fds[0],str,10000);

????? printf("%s",str);

????? close(fds[0]);

??? }

??? else if(pid>0)

??? {

??????? FILE*fp;

??????? char a[80];

??????? close(fds[0]);

??????? fp=(fopen("copy1.c","r"));

??????? if(fp==NULL)

??????? {

?????????? printf("can not open!!");

?????????? exit(0);

??????? }

??????? else

??????? {

??????? while(1)

??????? {

????????? if(fread(a,80,1,fp)==0) break;

????????? write(fds[1],a,sizeof(a));

??????? }

??????? }

????????? wait();

????????? close(fds[1]);

????????? fclose(fp);

????????? return 0;

??? }