网站优化案例,校园网络安全设计方案,wordpress分类使用不同模板,wordpress怎么改字体使用Posix共享内存区实现进程间通信
使用Posix共享内存区通常涉以下步骤:
进程A 调用shm_open 创建共享内存区进程A调用ftruncate修改共享内存区大小进程A 调用mmap将共享内存区映射到进程地址空间ptrA进程A 使用ptrA对共享内存区进程更改进程B 使用shm_open打开已有共享内存…使用Posix共享内存区实现进程间通信
使用Posix共享内存区通常涉以下步骤:
进程A 调用shm_open 创建共享内存区进程A调用ftruncate修改共享内存区大小进程A 调用mmap将共享内存区映射到进程地址空间ptrA进程A 使用ptrA对共享内存区进程更改进程B 使用shm_open打开已有共享内存区进程B 调用fstat获取共享内存区大小进程B 调用mmap将共享内存区映射到进程地址空间ptrB进程B 使用ptrB对共享内存区进行更改最后由进程A/B调用shm_unlink删除共享内存区
1、shm_open 创建/打开共享内存区
shm_open调用成功后返回共享内存区的文件描述符, 并在/dev/shm目录下生成相应的文件。
shm_open函数声明包含在文件 sys/mman.h 中;
#include sys/mman.h
#include sys/stat.h /* For mode constants */
#include fcntl.h /* For O_* constants */int shm_open(const char *name, int oflag, mode_t mode);oflag的值包含在文件 fcntl.h中 #define O_RDONLY 00 //只读
#define O_WRONLY 01 //只写
#define O_RDWR 02 //可读可写
#define O_CREAT 0100 //创建
#define O_EXCL 0200 //如果共享内存区已存在则返错误mode的值包含在文件sys/stat.h中 #define S_IRUSR __S_IREAD /* Read by owner. */
#define S_IWUSR __S_IWRITE /* Write by owner. */
#define S_IXUSR __S_IEXEC /* Execute by owner. */#define S_IRGRP (S_IRUSR 3) /* Read by group. */
#define S_IWGRP (S_IWUSR 3) /* Write by group. */
#define S_IXGRP (S_IXUSR 3) /* Execute by group. */#define S_IROTH (S_IRGRP 3) /* Read by others. */
#define S_IWOTH (S_IWGRP 3) /* Write by others. */
#define S_IXOTH (S_IXGRP 3) /* Execute by others. */2、ftruncate修改内存区大小
ftruncate包含在头文件unistd.h中
/* Truncate the file FD is open on to LENGTH bytes. */int ftruncate (int __fd, __off_t __length)fd:shm_ope返回的描述符
length:共享内存区的大小3、fstat获取文件大小
fstat包含在头文件sys/stat.h中
在打开已存在的共享内存区时可以用fstat获取共享内存区的大小。 /* Get file attributes for the file, device, pipe, or socketthat file descriptor FD is open on and put them in BUF. */
int fstat (int __fd, struct stat *__buf)fd:shm_open返回的描述符
stat.st_size是共享内存区的大小4、mmap将共享内存区映射到进程地址空间
mmap包含在头文件mman.h中 void *mmap (void *__addr, size_t __len, int __prot,int __flags, int __fd, __off_t __offset)参数
__addr: 映射到进程的地址,直接传入NULL就行。
__len: 共享内存区的大小。__prot: 权限
PROT_READ 可读
PROT_WRITE 可写
PROT_EXEC 可执行__flags:映射方式
MAP_SHARED: 当前进程所做的修改其他进程可见
MAP_PRIVATE:当前进程所做的修改其他进程不可见__fd: shm_open返回的描述符
__offset:偏移量,一般都传入05、shm_unlink删除共享内存区
shm_unlink和shm_open在同一文件中,用于删除共享内存区。
/* Remove shared memory segment. */
int shm_unlink (const char *__name);6、练习
进程shmserver创建共享内存区shmtest,并创建子进程等待其他进程向shmtest中写入数据。进程shmcli向共享内存区shmtest写入数据,并给进程shmserver发送信号。进程shmserver取出共享内存区shmtest中的数据并输出到窗口。
cond_h.h
#define COUNT 10typedef struct shm_block
{pthread_mutex_t mutex;pthread_cond_t cond;int arr[COUNT];int nput;int nread;int ncount;
}shm_block;void shm_block_init(shm_block* shm)
{pthread_mutexattr_t attr; pthread_mutexattr_init(attr);pthread_mutexattr_setpshared(attr, PTHREAD_PROCESS_SHARED); pthread_mutex_init(shm-mutex, attr);pthread_mutexattr_destroy(attr);pthread_condattr_t cond_attr;pthread_condattr_init(cond_attr);pthread_condattr_setpshared(cond_attr, PTHREAD_PROCESS_SHARED);pthread_cond_init(shm-cond, cond_attr);pthread_condattr_destroy(cond_attr);bzero(shm-arr, sizeof(shm-arr));shm-ncount 0;shm-nput 0;shm-nread 0;
}
shm_server.c
#includeunistd.h
#includepthread.h
#includemqueue.h
#includesys/mman.h
#includefcntl.h
#includesys/stat.h
#includestdio.h
#includestring.h
#includeerrno.h
#includestrings.h
#includewait.h
#includecond_h.hint main(int argc, char* argv[])
{ if (argc ! 2){printf(shmcreate [shmname]\n);return 0;}shm_block shm;shm_block_init(shm);int shmfd shm_open(argv[1], O_CREAT|O_EXCL|O_RDWR, S_IRUSR|S_IWUSR);if (shmfd -1){printf(%d : %s\n,__LINE__, strerror(errno));return -1;}printf(create shared memory %s. \n, argv[1]);if (ftruncate(shmfd, sizeof(shm_block)) 0){printf(%d : %s\n,__LINE__, strerror(errno));return -1;}shm_block* pBlock (shm_block*)mmap(NULL, sizeof(shm_block), PROT_WRITE|PROT_READ, MAP_SHARED, shmfd, 0);if (NULL pBlock){printf(%d : %s\n,__LINE__, strerror(errno));return -1;}close(shmfd);memcpy(pBlock, shm, sizeof(shm));int pid fork();if (pid 0){int fd shm_open(argv[1], O_RDWR, S_IRUSR|S_IWUSR);if (fd 0){printf(%d : %s\n,__LINE__, strerror(errno));return -1;}struct stat st;fstat(fd, st);printf(%d: st_size %d\n, __LINE__, st.st_size);shm_block *p (shm_block*)mmap(NULL, st.st_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);if (NULL p){printf(%d : %s\n,__LINE__, strerror(errno));return -1;}while (1){pthread_mutex_lock(p-mutex);while (p-ncount 0)pthread_cond_wait(p-cond, p-mutex);int value p-arr[p-nread];p-ncount--;p-nread;p-nread % COUNT; pthread_mutex_unlock(p-mutex);printf(%d: p-nread:%d, arr[nread] : %d\n,__LINE__, p-nread, value);}munmap(p, st.st_size);close(fd);return 0;}int stat_loc 0;waitpid(pid, stat_loc, 0);munmap(pBlock, sizeof(shm));if (WIFEXITED(stat_loc)) printf(Child process exited with status: %d\n, WEXITSTATUS(stat_loc));return 0;
}
shm_cli.c
#includesys/mman.h
#includesys/stat.h
#includefcntl.h
#includeunistd.h
#includepthread.h
#includestdlib.h
#includestdio.h
#includestring.h
#includeerrno.h
#includecond_h.hint main(int argc, char *argv[])
{if (argc ! 3){printf(cond_put shmname value);return -1;}char *shmname argv[1];int value atoi(argv[2]);int shmfd shm_open(shmname, O_RDWR, 0);if (-1 shmfd){printf(%d: %s\n, __LINE__, strerror(errno));return -1;}shm_block* p (shm_block*)mmap(NULL, sizeof(shm_block), PROT_READ|PROT_WRITE, MAP_SHARED, shmfd, 0);if (NULL p){printf(%d: %s\n, __LINE__, strerror(errno));return -1;}close(shmfd);pthread_mutex_lock(p-mutex);do{if (p-ncount COUNT)break;p-arr[p-nput] value;printf(count: %d, nput: %d, nread: %d,arr[nput]:%d\n, p-ncount, p-nput, p-nread,value);p-nput (p-nput 1) % COUNT;p-ncount;if (p-ncount 1)pthread_cond_signal(p-cond);} while (0);pthread_mutex_unlock(p-mutex);close(shmfd);return 0;
}使用方法 unlink /dev/shm/shmtest
gcc shm_server.c -lrt -lpthread -o shmserver
./shmserver shmtestgcc shm_cli.c -lrt -lpthread -o shmcli
./shmcli shmtest 33
./shmcli shmtest 34
./shmcli shmtest 35shmserver输出: create shared memory shmtest.
60: st_size 144
83: p-nread:1, arr[nread] : 33
83: p-nread:2, arr[nread] : 34
83: p-nread:3, arr[nread] : 35
