Linux中使用clone函数来创建线程

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Linux 上创建线程一般使用的是 pthread 库实际上 libc 也给我们提供了创建线程的函数那就是 clone

       int clone(int (*fn)(void *), void *child_stack,
                 int flags, void *arg, ...
                 /* pid_t *ptid, struct user_desc *tls, pid_t *ctid */ );

man 手册里面说的很清楚这个函数存在的意义就是实现线程当然这个函数不是 linux 的系统调用而是对系统调用的封装。

首先需要给新的线程创建个堆栈 &＃xff0c;使用函数 mmap ,这个函数常用来完成文件映射这里分配内存也是可以的

    void *pstack &＃61; (void *)mmap(NULL,
                                STACK_SIZE,
                                PROT_READ | PROT_WRITE ,
                                MAP_PRIVATE | MAP_ANONYMOUS | MAP_ANON ,//| MAP_GROWSDOWN ,
                                -1,
                                0);

通过指定 MAP_ANONYMOUS 标识系统就不会创建文件映射而仅仅分配内存

注意堆栈不要太小了不然会溢出的。。

然后调用 clone 函数

几个标识的意义

CLONE_VM (0x100) - tells the kernel to let the original process and the clone in the same memory space;CLONE_FS (0x200) - both get the same file system information;CLONE_FILES (0x400) - share file descriptors;CLONE_SIGHAND (0x800) - both processes share the same signal handlers;CLONE_THREAD (0x10000) - this tells the kernel, that both processes would belong to the same thread group (be threads within the same process);

在线程函数中直接 return 就可以退出线程了。。。。

使用 clone 的时候指定 CLONE_THREAD 那么以后就不能使用 wait 来等待这个线程了相当于 deteched .了。。。查看man 手册可以看到

A new thread created with CLONE_THREAD has the same parent process as the caller of clone() (i.e., like CLONE_PARENT), so that calls to getppid(2) return the same value for all of the threads in a thread group. When a CLONE_THREAD thread terminates, the thread that created it using clone() is not sent a SIGCHLD (or other termination) signal; nor can the status of such a thread be obtained using wait(2). (The thread is said to be detached.)

下面是我测试的代码

#define _GNU_SOURCE /* or _BSD_SOURCE or _SVID_SOURCE */ #include #include /* For SYS_xxx definitions */ #include #include #include #include #include #include #include #include #define STACK_SIZE 1024*1024*8 //8Mint thread_func(void *lparam) {printf("thread id %d \n", (int)syscall(SYS_gettid));printf("thread get param : %d \n", (int)lparam);sleep(1);return 0; }void child_handler(int sig) {printf("I got a SIGCHLD\n"); }int main(int argc, char **argv) {setvbuf(stdout, NULL, _IONBF, 0);signal(SIGCHLD, child_handler);//signal(SIGUSR1, SIG_IGN);void *pstack &＃61; (void *)mmap(NULL,STACK_SIZE,PROT_READ | PROT_WRITE ,MAP_PRIVATE | MAP_ANONYMOUS | MAP_ANON ,//| MAP_GROWSDOWN ,-1,0);if (MAP_FAILED !&＃61; pstack){int ret;printf("strace addr : 0x%X\n", (int)pstack);/*CLONE_VM (0x100) - tells the kernel to let the original process and the clone in the same memory space;CLONE_FS (0x200) - both get the same file system information;CLONE_FILES (0x400) - share file descriptors;CLONE_SIGHAND (0x800) - both processes share the same signal handlers;CLONE_THREAD (0x10000) - this tells the kernel, that both processes would belong to the same thread group (be threads within the same process);*/ret &＃61; clone(thread_func,(void *)((unsigned char *)pstack &＃43; STACK_SIZE),CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND |SIGCHLD,(void *)NULL);if (-1 !&＃61; ret){pid_t pid &＃61; 0;printf("start thread %d \n", ret);sleep(5);pid &＃61; waitpid(-1, NULL, __WCLONE | __WALL);printf("child : %d exit %s\n", pid,strerror(errno));}else{printf("clone failed %s\n", strerror(errno) );}}else{printf("mmap() failed %s\n", strerror(errno));}return 0; }