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

srs代码学习(2)- 线程模型_第1张图片


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


srs代码学习(2)- 线程模型_第2张图片


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,

srs代码学习(2)- 线程模型_第3张图片


这个类的是rtmp消息专用类,虽然在名字中没有体现出来。


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