Linux 内存映射

    mmap()将一个文件或者是其他对象映射到内存区	

函数说明：

#include<sys/mman.h>

void *mmap(void *start, size_t len, int prot, int flags, int fd, off_t offsize)

已PAGE_SIZE的整数倍进行映射，参数解读

start 指向预映射的地址的起始地址，通常该参数的值为NULL，由系统来决定，成功后返回该地址的值

len 代表将文件中多少数据映射到内存区

prot 映射区域的保护方式，其实就是页面的权限，由后面几个值进行组合 PROT_EXEC 页面区域可被执行  PROT_READ 页面区域可被读取 PROT_WRITE 页面可被写入 PROT_NONE 页面不能存取

fd 有效的文件描述符，一般由open函数返回，其值也可以为-1

#include <pthread.h>
#include <sys/mman.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>	
#include <unistd.h>
#include <sys/wait.h>
#include <semaphore.h>
#include <sys/types.h>
#include <fcntl.h>

#define FILE_MODE 0644
#define FILE_NAME "mmap"
int main(int argc, char **argv)
{
    int fd, i ,nloop, zero = 0;
	void *ptr;
	sem_t *pMutex;
    
	if(argc != 3)
    {
        printf("argc error %d\n", argc);
        exit(0);
    }
        
    nloop = atoi(argv[2]);  
    fd = open(argv[1], O_RDWR|O_CREAT, FILE_MODE);
    write(fd, &zero, sizeof(int));
	ptr = mmap(NULL, sizeof(int), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
    close(fd);
    
    signal(SIGCHLD,SIG_IGN);
    
    pMutex = sem_open(FILE_NAME, O_CREAT|O_EXCL, FILE_MODE, 1);   
    if(pMutex == SEM_FAILED)
    {   
        printf("semopen error\n");
        exit(-1);
    }
    
    sem_unlink(FILE_NAME);
    setbuf(stdout, NULL);
    if(fork() == 0)
    {
        for(i = 0; i < nloop; i++)
        {
            sem_wait(pMutex);
            printf("child %d\n", (*(int *)ptr)++);
            sem_post(pMutex);
        }
    }
    for(i = 0; i < nloop; i++)
    {
        sem_wait(pMutex);
        printf("child %d\n", (*(int *)ptr)++);
        sem_post(pMutex);
    }
    
    sem_close(pMutex);
    exit(0);    
}

Makefile

TARGET = mmap
COMPILE = -fPIC
COMPILE += -c -g
CC = g++
GCC = gcc
LINK = -lpthread
BUILD_CACHE_DIR=.buildCacheDir

ALLSRC = $(wildcard *.c)
ALL_OBJ = $(patsubst %.c, $(BUILD_CACHE_DIR)/%.o, $(filter %.c, $(ALLSRC)))
.PHYONE:all
all:createDir $(TARGET)
createDir:
	@mkdir -p $(BUILD_CACHE_DIR) 2>/dev/null
#	@mkdir -p $(INSTALL_PATH)/ 2>/dev/null
	
	
$(TARGET):$(ALL_OBJ)
	@echo 
	@echo "------------------------------------------------------------------"
	@echo "==== Linking $@ === "
	@echo "------------------------------------------------------------------"
	$(CC) $(ALL_OBJ) $(LINK) -o $@
	@echo "------------------------------------------------------------------"
	
#编译规则
$(BUILD_CACHE_DIR)/%.o:%.cpp
	$(CC) $(COMPILE) $< -o $@

$(BUILD_CACHE_DIR)/%.o:%.c
	$(GCC) $(COMPILE) $< -o $@

clean:
	-rm -rf $(BUILD_CACHE_DIR)