Android C++系列：Linux线程（三）线程属性

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"linux下线程的属性是可以根据实际项目需要，进行设置，之前我们讨论的线程都是采用线程的默认属性，默认属性已经可以解决绝大多数开发时遇到的问 题。如我们对程序的性能提出更高的要求那么需要设置线程属性，比如可以通过设置线程栈的大小来降低内存的使用，增加最大线程个数。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"text"},"content":[{"type":"text","text":"typedef struct {\n int etachstate; //线程的分离状态\n int schedpolicy; //线程调度策略\n structsched_param schedparam; //线程的调度参数\n int inheritsched; //线程的继承性\n int scope;//线程的作用域\n size_t guardsize;//线程栈末尾的警戒缓冲区大小\n int stackaddr_set; //线程的栈设置\n void* stackaddr; //线程栈的位置\n size_t stacksize; //线程栈的大小 \n}pthread_attr_t; \n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"注:目前线程属性在内核中不是直接这么定义的，抽象太深不便分析，为方便理解，我们使用早期的线程属性定义，两者之间定义的主要元素差别不大。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"属性值不能直接设置，须使用相关函数进行操作，初始化的函数为pthread_attr_init， 这个函数必须在pthread_create函数之前调用。之后须用pthread_attr_destroy函数来释 放资源。线程属性主要包括如下属性:作用域(scope)、栈尺寸(stack size)、栈地址 (stack address)、优先级(priority)、分离的状态(detached state)、调度策略和 参数(scheduling policy and parameters)。默认的属性为非绑定、非分离、缺省M的堆 栈、与父进程同样级别的优先级。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"1. 线程属性初始化","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"先初始化线程属性，再pthread_create创建线程","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"text"},"content":[{"type":"text","text":"#include \nint pthread_attr_init(pthread_attr_t *attr); //初始化线程属性\nint pthread_attr_destroy(pthread_attr_t *attr); //销毁线程属性所占用的资源\n","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"2. 线程的分离状态(detached state)","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"线程的分离状态决定一个线程以什么样的方式来终止自己。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"非分离状态:线程的默认属性是非分离状态，这种情况下，原有的线程等待创建的线程 结束。只有当pthread_join()函数返回时，创建的线程才算终止，才能释放自己占用的系统 资源。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"分离状态:分离线程没有被其他的线程所等待，自己运行结束了，线程也就终止了，马上释放系统资源。应该根据自己的需要，选择适当的分离状态。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"线程分离状态的函数:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"text"},"content":[{"type":"text","text":"#include \nint pthread_attr_setdetachstate(pthread_attr_t *attr, int detachstate); //设置线程属性，分离or非分离\nint pthread_attr_getdetachstate(pthread_attr_t *attr, int *detachstate); //获取程属性，分离or非分离\npthread_attr_t *attr:被已初始化的线程属性\nint *detachstate:可选为PTHREAD_CREATE_DETACHED(分离线程)和 PTHREAD _CREATE_JOINABLE(非分离线程)\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这里要注意的一点是，如果设置一个线程为分离线程，而这个线程运行又非常快， 它很可能在pthread_create函数返回之前就终止了，它终止以后就可能将线程号和系统资源移交给其他的线程使用，这样调用pthread_create的线程就得到了错误的线程号。 要避免这种情况可以采取一定的同步措施，最简单的方法之一是可以在被创建的线程里调用pthread_cond_timedwait函数，让这个线程等待一会儿，留出足够的时间让函数 pthread_create返回。设置一段等待时间，是在多线程编程里常用的方法。但是注意不要使 用诸如wait()之类的函数，它们是使整个进程睡眠，并不能解决线程同步的问题。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"3. 线程的栈地址(stack address)","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"POSIX.1定义了两个常量","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"_POSIX_THREAD_ATTR_STACKADDR","attrs":{}}],"attrs":{}},{"type":"text","text":" 和","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"_POSIX_THREAD_ATTR_STACKSIZE","attrs":{}}],"attrs":{}},{"type":"text","text":" 检测系统是否支持栈属性。也可以给sysconf函数传递_SC_THREAD_ATTR_STACKADDR或 _SC_THREAD_ATTR_STACKSIZE 来进行检测。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"当进程栈地址空间不够用时，指定新建线程使用由malloc分配的空间作为自己的栈空 间。通过pthread_attr_setstackaddr和pthread_attr_getstackaddr两个函数分别设置和获 取线程的栈地址。传给pthread_attr_setstackaddr函数的地址是缓冲区的低地址(不一定 是栈的开始地址，栈可能从高地址往低地址增长)。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"text"},"content":[{"type":"text","text":"include \nint pthread_attr_setstackaddr(pthread_attr_t *attr, void *stackaddr);\nint pthread_attr_getstackaddr(pthread_attr_t *attr, void **stackaddr);\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"attr: 指向一个线程属性的指针","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"stackaddr: 返回获取的栈地址 返回值:若是成功返回0,否则返回错误的编号","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"说 明:函数已过时，一般用下面讲到的pthread_attr_getstack来代替","attrs":{}}]}]}],"attrs":{}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"4. 线程的栈大小(stack size)","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"当系统中有很多线程时，可能需要减小每个线程栈的默认大小，防止进程的地址空间不 够用,当线程调用的函数会分配很大的局部变量或者函数调用层次很深时，可能需要增大线 程栈的默认大小。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"函数pthread_attr_getstacksize和 pthread_attr_setstacksize提供设置。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"text"},"content":[{"type":"text","text":"#include \nint pthread_attr_setstacksize(pthread_attr_t *attr, size_t stacksize); \nint pthread_attr_getstacksize(pthread_attr_t *attr, size_t *stacksize);\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"attr 指向一个线程属性的指针","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"stacksize 返回线程的堆栈大小","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"返回值:若是成功返回0,否则返回错误的编号","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"除上述对栈设置的函数外，还有以下两个函数可以获取和设置线程栈属性","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"text"},"content":[{"type":"text","text":"#include \nint pthread_attr_setstack(pthread_attr_t *attr, void *stackaddr, size_t stacksize); \nint pthread_attr_getstack(pthread_attr_t *attr, void **stackaddr, size_t *stacksize);\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"attr 指向一个线程属性的指针","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"stackaddr 返回获取的栈地址","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"stacksize 返回获取的栈大小","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"返回值:若是成功返回0,否则返回错误的编号","attrs":{}}]}]}],"attrs":{}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"5. 线程属性控制实例","attrs":{}}]},{"type":"codeblock","attrs":{"lang":"text"},"content":[{"type":"text","text":"#include \n#include \n#include \n#include \n#define SIZE 0x10000\nint print_ntimes(char *str) {\n sleep(1); \n printf(\"%s\\n\", str); \n return 0;\n}\nvoid *th_fun(void *arg) {\n int n = 3; \n while (n--)\n print_ntimes(\"hello xwp\\n\"); \n}\n \nint main(void){\n pthread_t tid;\n int err, detachstate, i = 1; \n pthread_attr_t attr;\n size_t stacksize;\n void *stackaddr;\n pthread_attr_init(&attr);\n pthread_attr_getstack(&attr, &stackaddr, &stacksize); \n printf(\"stackadd=%p\\n\", stackaddr); \n printf(\"stacksize=%x\\n\", (int)stacksize);\n pthread_attr_getdetachstate(&attr, &detachstate); \n if (detachstate == PTHREAD_CREATE_DETACHED)\n printf(\"thread detached\\n\");\n else if (detachstate == PTHREAD_CREATE_JOINABLE)\n printf(\"thread join\\n\"); \n else\n printf(\"thread un known\\n\");\n /* 设置线程分离属性 */\n pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED); \n while (1) {\n /* 在堆上申请内存，指定线程栈的起始地址和大小 */ \n stackaddr = malloc(SIZE);\n if (stackaddr == NULL) {\n perror(\"malloc\");\n exit(1); \n }\n stacksize = SIZE;\n pthread_attr_setstack(&attr, stackaddr, stacksize);\n err = pthread_create(&tid, &attr, th_fun, NULL); \n if (err != 0) {\n printf(\"%s\\n\", strerror(err));\n exit(1); \n }\n printf(\"%d\\n\", i++); \n }\n pthread_attr_destroy(&attr);\n return 0;\n}\n","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"6. 线程其他注意事项","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"6.1 NPTL","attrs":{}}]},{"type":"numberedlist","attrs":{"start":1,"normalizeStart":1},"content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"察看当前pthread库版本","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"getconf GNU_LIBPTHREAD_VERSION","attrs":{}}],"attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"NPTL实现机制(POSIX),Native POSIX Thread Library","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"使用线程库时gcc指定 -lpthread","attrs":{}}]}]}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"6.2 线程终止方式","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果需要只终止某个线程而不终止整个进程，可以有三种方法:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"numberedlist","attrs":{"start":1,"normalizeStart":1},"content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"从线程主函数return。这种方法对主控线程不适用，从main函数return相当于调用 exit；","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"一个线程可以调用pthread_cancel终止同一进程中的另一个线程；","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"线程可以调用pthread_exit终止自己。","attrs":{}}]}]}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"6.3 细节注意","attrs":{}}]},{"type":"numberedlist","attrs":{"start":1,"normalizeStart":1},"content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"主线程退出其他线程不退出，主线程应调用ptrhed_exit ；","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"避免僵线程：","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":1,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"join","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":1,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"pthread_deatch","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":1,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"pthread_create指定分离属性","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":1,"number":4,"align":null,"origin":null},"content":[{"type":"text","text":"被join线程可能在join函数返回前就释放完自己的所有内存资源，所以不应当返回被回收线程栈中的值;","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"malloc和mmap申请的内存可以被其他线程释放；","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":4,"align":null,"origin":null},"content":[{"type":"text","text":"如果线程终止时没有释放加锁的互斥量，则该互斥量不能再被使用；","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":5,"align":null,"origin":null},"content":[{"type":"text","text":"应避免在多线程模型中调用fork除非，马上exec，子进程中只有调用fork的线程存在，其他线程在子进程中均pthread_exit；","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":6,"align":null,"origin":null},"content":[{"type":"text","text":"信号的复杂语义很难和多线程共存，应避免在多线程引入信号机制","attrs":{}}]}]}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"7. 总结","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本文介绍了线程属性：线程属性初始化、线程的分离状态、线程的栈地址、线程的栈大小；还介绍了线程的NPTL、线程终止方式、注意细节等注意事项。","attrs":{}}]}]}