共享内存

多个进程共享同一块内存区域，必然需要某种同步机制，互斥锁和信号量都可以。

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <semaphore.h>
#include <fcntl.h>

#define   SEM_NAME         "mysem"
#define   FILE_MODE   (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)
int   count = 0;

int main(int argc,char* argv[])
{
    int  i,nloop;
    sem_t *mutex;
    if(argc != 2)
    {
        printf("usage: incrl <#loops>");
        exit(0);
    }
    nloop = atoi(argv[1]);
        //创建有名信号量
    mutex = sem_open(SEM_NAME,O_RDWR|O_CREAT|O_EXCL,FILE_MODE,1);
    sem_unlink(SEM_NAME);
        //将stdout设置为非缓冲的
    setbuf(stdout,NULL);
       //子进程开始执行增加1
    if(fork() == 0)
    {
        for(i = 0;i<nloop;++i)
        {
            sem_wait(mutex);
            printf("child: %d\n",count++);
            sem_post(mutex);
        }
        exit(0);
    }
       //父进程执行增加1操作
    for(i = 0;i<nloop;++i)
    {
        sem_wait(mutex);
        printf("parent: %d\n",count++);
        sem_post(mutex);
    }
        //等待子进程退出
    wait(NULL);
    exit(0);
}

gcc demo.c -o app -lphthread -std=c99
./app 10

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <semaphore.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <errno.h>

#define   SEM_NAME         "mysem"
#define   FILE_MODE   (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)

int main(int argc,char* argv[])
{
    int     fd,i,nloop,zero = 0;
    int      *ptr;
    sem_t   *mutex;
    if(argc != 3)
    {
        printf("usage: incrl <#loops>");
        exit(0);
    }
    nloop = atoi(argv[2]);
    //打开文件
    fd = open(argv[1],O_RDWR|O_CREAT,FILE_MODE);
    //向文件中写入0值
    write(fd,&zero,sizeof(int));
    //将文件映射到进程地址空间，返回被映射区的起始地址
    ptr = mmap(NULL,sizeof(int),PROT_READ| PROT_WRITE,MAP_SHARED,fd,0);
    if(ptr == MAP_FAILED)
    {
        perror("mmap() error");
        exit(0);
    }
    close(fd);
    mutex = sem_open(SEM_NAME,O_RDWR|O_CREAT|O_EXCL,FILE_MODE,1);
    sem_unlink(SEM_NAME);
    setbuf(stdout,NULL);
    if(fork() == 0)
    {
        for(i = -0;i<nloop;++i)
        {
            sem_wait(mutex);
            printf("child: %d\n",(*ptr)++);
            sem_post(mutex);
        }
        exit(0);
    }
    for(i = 0;i<nloop;++i)
    {
        sem_wait(mutex);
        printf("parent: %d\n",(*ptr)++);
        sem_post(mutex);
    }
    wait(NULL);
    exit(0);
}

gcc demo1.c -o app2 -lpthread -stc=c99

./app2 app 10

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <semaphore.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <errno.h>

#define   SEM_NAME         "mysem"
#define   FILE_MODE   (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)

//共享内存结构
struct shared
{
    sem_t mutex;       //信号量
    int count;         //计数器
}shared;

int main(int argc,char* argv[])
{
    int     fd,i,nloop;
    struct  shared *ptr;
    if(argc != 3)
    {
        printf("usage: incrl <#loops>");
        exit(0);
    }
    nloop = atoi(argv[2]);
    fd = open(argv[1],O_RDWR|O_CREAT,FILE_MODE);
    write(fd,&shared,sizeof(struct shared));
    ptr = mmap(NULL,sizeof(struct shared),PROT_READ| PROT_WRITE,MAP_SHARED,fd,0);
    if(ptr == MAP_FAILED)
    {
        perror("mmap() error");
        exit(0);
    }
    close(fd);
    sem_init(&ptr->mutex,1,1);
    setbuf(stdout,NULL);
    if(fork() == 0)
    {
        for(i = -0;i<nloop;++i)
        {
            sem_wait(&ptr->mutex);
            printf("child: %d\n",ptr->count++);
            sem_post(&ptr->mutex);
        }
        exit(0);
    }
    for(i = 0;i<nloop;++i)
    {
        sem_wait(&ptr->mutex);
        printf("parent: %d\n",ptr->count++);
        sem_post(&ptr->mutex);
    }
    wait(NULL);
    exit(0);
}

gcc demo1.c -o app2 -lpthread -stc=c99

./app2 app 10

以上可以使用匿名映射

// 方式一
int *ptr;
ptr = mmap(NULL,sizeof(int),PROT_READ|PROT_WRITE,MAP_SHARED | MAP_ANON,-1,0);
// 方式二
int *ptr;
fd = open("dev/zero",O_RDWR);
ptr = mmap(NULL,sizeof(int),PROT_READ | PROT_WRITE,MAP_SHARED,fd,0);