系统编程之进程通信 共享内存

structshared_use_st

{

intwritten_by_you;//互斥控制有读写两进程改写（1读进程0写进程）

charsome_text[TEXT_SZ];//数据部分

};

/*shm1.c*/

/*读进程

*/

#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"shm_com.h"

intmain(void)

{

intrunning=1;

void*shared_memory=(void*)0;

structshared_use_st*shared_stuff;

intshmid;

/*创建共享内存*/

shmid=shmget((key_t)1234,sizeof(structshared_use_st),0666|IPC_CREAT);

if(shmid==-1)

{

fprintf(stderr,"shmgetfailed\n");

exit(EXIT_FAILURE);

}

/*映射（附加）共享内存*/

shared_memory=shmat(shmid,(void*)0,0);

if(shared_memory==(void*)-1)

{

fprintf(stderr,"shmatfailed\n");

exit(EXIT_FAILURE);

}

printf("Memoryattachedat%X\n",(int)shared_memory);

/*让结构体指针指向这块共享内存*/

shared_stuff=(structshared_use_st*)shared_memory;

/*控制读写顺序*/

shared_stuff->written_by_you=0;

/*循环的从共享内存中读数据，直到读到“end”为止*/

while(running)

{

if(shared_stuff->written_by_you)

{

printf("Youwrote:%s",shared_stuff->some_text);

sleep(1);/*读进程睡一秒，同时会导致写进程睡一秒（信号量为1），这样做到了读了之后再写*/

shared_stuff->written_by_you=0;

if(strncmp(shared_stuff->some_text,"end",3)==0)

{

running=0;//结束循环

}

}

}

/*分离共享内存*/

if(shmdt(shared_memory)==-1)

{

fprintf(stderr,"shmdtfailed\n");

exit(EXIT_FAILURE);

}

exit(EXIT_SUCCESS);

}

/*shm2.c*/

/*写进程*/

#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"shm_com.h"

intmain()

{

intrunning=1;

void*shared_memory=(void*)0;

structshared_use_st*shared_stuff;

charbuffer[BUFSIZ];

intshmid;

/*创建共享内存*/

shmid=shmget((key_t)1234,sizeof(structshared_use_st),0666|IPC_CREAT);

if(shmid==-1)

{

fprintf(stderr,"shmgetfailed\n");

exit(EXIT_FAILURE);

}

/*映射（附加）共享内存*/

shared_memory=shmat(shmid,(void*)0,0);

if(shared_memory==(void*)-1)

{

fprintf(stderr,"shmatfailed\n");

exit(EXIT_FAILURE);

}

printf("Memoryattachedat%X\n",(int)shared_memory);

/*让结构体指针指向这块共享内存*/

shared_stuff=(structshared_use_st*)shared_memory;

/*循环的向共享内存中写数据。直到写入的为“end”为止*/

while(running)

{

while(shared_stuff->written_by_you==1)

{

sleep(1);//等到读进程读完之后再写

printf("waittingforclient..\n");

}

printf("Entersometst:");

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;//结束循环

}

}

/*分离共享内存*/

if(shmdt(shared_memory)==-1)

{

fprintf(stderr,"shmdtfailed\n");

exit(EXIT_FAILURE);

}

/*删除共享内存*/

if(shmctl(shmid,IPC_RMID,0)<0)//等到所有已附加进程都分离才删除

{

fprintf(stderr,"shmctlerror\n");

exit(EXIT_FAILURE);

}

exit(EXIT_SUCCESS);

}