Linux process communication mode--shared memory

1. Concept

Different processes see common areas

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2. Features

(1) is the fastest way to communicate between processes, mapping different memory (two copies less)

(2) does not provide any synchronous mutual exclusion mechanism, also does not maintain itself

(3) Simple interface

3. Means of communication

Provided by file system--pipeline

Supplied by System V-Message Queuing, semaphores, shared memory

shared memory combined with semaphores

4, realize Shmat, SHMDT

At: Hook up dt: go to hook up

0	1	2	1	0
Create	Hook up	Seen by another process	Exit	And then quit.

Code implementation:

Shm.h file:

#ifndef __shm__
#define __SHM__

#include <stdio.h>
#include <sys/shm.h>
#include <sys/ipc.h>
#include <sys/wait.h>
#include <unistd.h>

#define __PATH__ "."
#define __PROJECT__ 8888
#define __SHM_SIZE__ 4096

int Get_shm ();
char* At_shm ();
int Delete_shm ();
int Rm_shm ();
#endif

SHM.C file:

#include "shm.h"
int Get_shm ()
{
key_t Key=ftok (__path__,__project__);
int flag=ipc_creat|0666;
int Shm_id=shmget (KEY,__SHM_SIZE__,FLAG);
if (shm_id==-1) {
printf ("Get share Memory error!\n");
}else{
printf ("Get share Memory success!\n");
}
return shm_id;
}

char *at_shm (int shm_id)
{
Return (char*) Shmat (shm_id,null,0);
}

int Delete_shm (char *addr)
{
return Shmdt (addr);
}

If Success,return (), Else return-1
int rm_shm (int shm_id)
{
Return Shmctl (Shm_id,ipc_rmid,null);
}

TEST_SHM.C file:

#include "shm.h"

int main ()
{
int Shm_id=get_shm ();
pid_t id=fork ();
if (id<0) {
printf ("fork error\n");
return 1;
}else if (id==0) {//child
Char *buf=at_shm (shm_id);
int i=0;
while (i<4096) {
buf[i]= ' X ';
i++;
}
buf[4096]= ' + ';
DELETE_SHM (BUF);
}else{//father
Char *buf=at_shm (shm_id);
Sleep (5);
printf ("%s\n", buf);
DELETE_SHM (BUF);
Waitpid (id,null,0);
RM_SHM (shm_id);
}
return 0;
}

Makefile File:

TEST_SHM:SHM.C TEST_SHM.C
Gcc-o [email protected] $^
. Phony:clean
Clean
Rm-f TEST_SHM

Operation Result:

[[email protected] shm]$ make

Gcc-o Test_shm shm.c TEST_SHM.C

[Email protected] shm]$./TEST_SHM

Get Share Memory success!

[Email protected] shm]$

Linux process communication mode--shared memory