共用記憶體 進程通訊

參考地址：http://www.ibm.com/developerworks/cn/linux/l-ipc/part5/index1.html?ca=drs-

main.c

/*-------------map_normalfile1.c-----------*/
#include <sys/mman.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
typedef struct{
char name[4];
int  age;
}people;
main(int argc, char** argv) // map a normal file as shared mem:
{
int fd,i;
  people *p_map;
char temp;

  fd=open(argv[1],O_CREAT|O_RDWR|O_TRUNC,00777);
  lseek(fd,sizeof(people)*5-1,SEEK_SET);
  write(fd,"",1);

  p_map = (people*) mmap( NULL,sizeof(people)*10,PROT_READ|PROT_WRITE,
        MAP_SHARED,fd,0 );
  close( fd );
  temp = 'a';
for(i=0; i<10; i++)
  {
    temp += 1;
    memcpy( ( *(p_map+i) ).name, &temp,2 );
    ( *(p_map+i) ).age = 20+i;
  }
  printf(" initialize over \n ");
  sleep(10);
  munmap( p_map, sizeof(people)*10 );
  printf( "umap ok \n" );
}

 

client.c

/*-------------map_normalfile2.c-----------*/
#include <sys/mman.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
typedef struct{
char name[4];
int  age;
}people;
main(int argc, char** argv)  // map a normal file as shared mem:
{
int fd,i;
  people *p_map;
  fd=open( argv[1],O_CREAT|O_RDWR,00777 );
  p_map = (people*)mmap(NULL,sizeof(people)*10,PROT_READ|PROT_WRITE,
       MAP_SHARED,fd,0);
for(i = 0;i<10;i++)
  {
  printf( "name: %s age %d;\n",(*(p_map+i)).name, (*(p_map+i)).age );
  }
  munmap( p_map,sizeof(people)*10 );
}

 

Makefile

all:main
main:
    gcc -g -Wall -O0 main.c -o main

client:
    gcc -g -Wall -O0 client.c -o client

clean:
    rm *.o main client

 

分別把兩個程式編譯成可執行檔map_normalfile1和map_normalfile2後，在一個終端上先運行./map_normalfile2 /tmp/test_shm，程式輸出結果如下：

initialize overumap ok

 

在map_normalfile1輸出initialize over 之後，輸出umap ok之前，在另一個終端上運行map_normalfile2 /tmp/test_shm，將會產生如下輸出(為了節省空間的，輸出結果為稍作整理後的結果)：

name: bage 20;name: cage 21;name: dage 22;name: eage 23;name: fage 24;name: gage 25;name: hage 26;name: Iage 27;name: jage 28;name: kage 29;

 

在map_normalfile1 輸出umap ok後，運行map_normalfile2則輸出如下結果：

name: bage 20;name: cage 21;name: dage 22;name: eage 23;name: fage 24;name:age 0;name:age 0;name:age 0;name:age 0;name:age 0;