srs代码学习（2）- 线程模型

代码阅读到现在。发现srs有两大类线程。一个是主线程的逻辑。

一个是监听线程簇。结构图如下

一定还有第三种线程模型，负责底层的多路分发。今天还没有发现。

2016.08.25--21:00

仔细阅读了state-threads的介绍，特别是setjmp()和longjmp（）函数，发现了一下代码

_st_thread_t *st_thread_create(void *(*start)(void *arg), void *arg,       int joinable, int stk_size){  _st_thread_t *thread;  _st_stack_t *stack;  void **ptds;  char *sp;#ifdef __ia64__  char *bsp;#endif  /* Adjust stack size */  if (stk_size == 0)    stk_size = ST_DEFAULT_STACK_SIZE;  stk_size = ((stk_size + _ST_PAGE_SIZE - 1) / _ST_PAGE_SIZE) * _ST_PAGE_SIZE;  stack = _st_stack_new(stk_size);  if (!stack)    return NULL;  /* Allocate thread object and per-thread data off the stack */#if defined (MD_STACK_GROWS_DOWN)  sp = stack->stk_top;#ifdef __ia64__  /*   * The stack segment is split in the middle. The upper half is used   * as backing store for the register stack which grows upward.   * The lower half is used for the traditional memory stack which   * grows downward. Both stacks start in the middle and grow outward   * from each other.   */  sp -= (stk_size >> 1);  bsp = sp;  /* Make register stack 64-byte aligned */  if ((unsigned long)bsp & 0x3f)    bsp = bsp + (0x40 - ((unsigned long)bsp & 0x3f));  stack->bsp = bsp + _ST_STACK_PAD_SIZE;#endif  sp = sp - (ST_KEYS_MAX * sizeof(void *));  ptds = (void **) sp;  sp = sp - sizeof(_st_thread_t);  thread = (_st_thread_t *) sp;  /* Make stack 64-byte aligned */  if ((unsigned long)sp & 0x3f)    sp = sp - ((unsigned long)sp & 0x3f);  stack->sp = sp - _ST_STACK_PAD_SIZE;#elif defined (MD_STACK_GROWS_UP)  sp = stack->stk_bottom;  thread = (_st_thread_t *) sp;  sp = sp + sizeof(_st_thread_t);  ptds = (void **) sp;  sp = sp + (ST_KEYS_MAX * sizeof(void *));  /* Make stack 64-byte aligned */  if ((unsigned long)sp & 0x3f)    sp = sp + (0x40 - ((unsigned long)sp & 0x3f));  stack->sp = sp + _ST_STACK_PAD_SIZE;#else#error Unknown OS#endif  memset(thread, 0, sizeof(_st_thread_t));  memset(ptds, 0, ST_KEYS_MAX * sizeof(void *));  /* Initialize thread */  thread->private_data = ptds;  thread->stack = stack;  thread->start = start;  thread->arg = arg;#ifndef __ia64__  _ST_INIT_CONTEXT(thread, stack->sp, _st_thread_main);#else  _ST_INIT_CONTEXT(thread, stack->sp, stack->bsp, _st_thread_main);#endif  /* If thread is joinable, allocate a termination condition variable */  if (joinable) {    thread->term = st_cond_new();    if (thread->term == NULL) {      _st_stack_free(thread->stack);      return NULL;    }  }  /* Make thread runnable */  thread->state = _ST_ST_RUNNABLE;  _st_active_count++;  _ST_ADD_RUNQ(thread);#ifdef DEBUG  _ST_ADD_THREADQ(thread);#endif  return thread;}

这个是创建线程的函数。仔细搜索其中的thread变量，会发现其实本身并没有创建一个新的线程，额只是在堆上分配了一个新的stack.代码如下

thread = (_st_thread_t *) sp;

这个thread只是一个结构体。

这么说来，整个程序都是在一个主线程上做调用。而不存在线程的切换。一系列同步锁等问题。这一点还有在以后代码阅读中在做体会。

虽然大概搞明白了，但这里面的理念包括代码，已经超越我的认知了。这怎么可能呢？

2016-08-26 15:00

发现了一个新的线程簇，用了做rtmp协议的收发，结构图如下

分析过好，发现这个类线程簇是在上一类线程的基础上。增加了rtmpser模块接收或者发送数据，由于有了消息的概念所以多了几个新的类，包括SrsCommonMessage类，

这个类的是rtmp消息专用类，虽然在名字中没有体现出来。