Nodejs探秘之深入理解单线程实现高并发原理

目录

• 前言
• 架构一览
• 与操作系统交互
• 单线程
• 事件驱动/事件循环
• Node.js 中的事件循环**的实现：**
• Event Loop的执行顺序
• uv__io_poll阶段
• 总结

async function open(path, flags, mode) {  mode = modeNum(mode, 0o666);  path = getPathFromURL(path);
  validatePath(path);
  validateUint32(mode, 'mode');
  return new FileHandle(
    await binding.openFileHandle(pathModule.toNamespacedPath(path),
             stringToFlags(flags),             mode, kUsePromises));
}

static void Open(const FunctionCallbackInfo& args) {  Environment* env = Environment::GetCurrent(args);  const int argc = args.Length();  if (req_wrap_async != nullptr) {  // open(path, flags, mode, req)    AsyncCall(env, req_wrap_async, args, "open", UTF8, AfterInteger,
              uv_fs_open, *path, flags, mode);
  } else {  // open(path, flags, mode, undefined, ctx)    CHECK_EQ(argc, 5);    FSReqWrapSync req_wrap_sync;    FS_SYNC_TRACE_BEGIN(open);    int result = SyncCall(env, args[4], &req_wrap_sync, "open",
                          uv_fs_open, *path, flags, mode);    FS_SYNC_TRACE_END(open);
    args.GetReturnValue().Set(result);
  }
}

/* Open the destination file. */
  dstfd = uv_fs_open(NULL,                     &fs_req,
                     req->new_path,
                     dst_flags,
                     statsbuf.st_mode,                     NULL);
  uv_fs_req_cleanup(&fs_req);

var http = require('http');function sleep(time) {    var _exit = Date.now() + time * 1000;    while( Date.now() < _exit ) {}    return ;
}var server = http.createServer(function(req, res){
    sleep(10);
    res.end('server sleep 10s');
});
server.listen(8080);

Environment* CreateEnvironment(IsolateData* isolate_data,
                               Local context,                               int argc,                               const char* const* argv,                               int exec_argc,                               const char* const* exec_argv) {
  Isolate* isolate = context->GetIsolate();  HandleScope handle_scope(isolate);
  Context::Scope context_scope(context);  auto env = new Environment(isolate_data, context,
                             v8_platform.GetTracingAgent());
  env->Start(argc, argv, exec_argc, exec_argv, v8_is_profiling);  return env;
}

{
    SealHandleScope seal(isolate);
    bool more;
    env.performance_state()->Mark(
        node::performance::NODE_PERFORMANCE_MILESTONE_LOOP_START);
    do {
      uv_run(env.event_loop(), UV_RUN_DEFAULT);
      v8_platform.DrainVMTasks(isolate);
      more = uv_loop_alive(env.event_loop());      if (more)
        continue;
      RunBeforeExit(&env);      // Emit `beforeExit` if the loop became alive either after emitting
      // event, or after running some callbacks.
      more = uv_loop_alive(env.event_loop());
    } while (more == true);
    env.performance_state()->Mark(
        node::performance::NODE_PERFORMANCE_MILESTONE_LOOP_EXIT);
  }
  env.set_trace_sync_io(false);
  const int exit_code = EmitExit(&env);
  RunAtExit(&env);

int uv_run(uv_loop_t* loop, uv_run_mode mode) {  int timeout;  int r;  int ran_pending;//首先检查我们的loop还是否活着//活着的意思代表loop中是否有异步任务//如果没有直接就结束
  r = uv__loop_alive(loop);  if (!r)
    uv__update_time(loop);//传说中的事件循环，你没看错了啊！就是一个大while
  while (r != 0 && loop->stop_flag == 0) { //更新事件阶段
    uv__update_time(loop); //处理timer回调
    uv__run_timers(loop); //处理异步任务回调 
    ran_pending = uv__run_pending(loop);//没什么用的阶段
    uv__run_idle(loop);
    uv__run_prepare(loop);    //这里值得注意了
    //从这里到后面的uv__io_poll都是非常的不好懂的
    //先记住timeout是一个时间
    //uv_backend_timeout计算完毕后，传递给uv__io_poll
    //如果timeout = 0,则uv__io_poll会直接跳过
    timeout = 0;    if ((mode == UV_RUN_ONCE && !ran_pending) || mode == UV_RUN_DEFAULT)
      timeout = uv_backend_timeout(loop);
    uv__io_poll(loop, timeout);    //就是跑setImmediate
    uv__run_check(loop);    //关闭文件描述符等操作
    uv__run_closing_handles(loop);    if (mode == UV_RUN_ONCE) {      /* UV_RUN_ONCE implies forward progress: at least one callback must have
       * been invoked when it returns. uv__io_poll() can return without doing
       * I/O (meaning: no callbacks) when its timeout expires - which means we
       * have pending timers that satisfy the forward progress constraint.
       *
       * UV_RUN_NOWAIT makes no guarantees about progress so it's omitted from
       * the check.
       */
      uv__update_time(loop);
      uv__run_timers(loop);
    }
    r = uv__loop_alive(loop);    if (mode == UV_RUN_ONCE || mode == UV_RUN_NOWAIT)      break;
  }  /* The if statement lets gcc compile it to a conditional store. Avoids
   * dirtying a cache line.
   */
  if (loop->stop_flag != 0)    loop->stop_flag = 0;  return r;
}

int uv_backend_timeout(const uv_loop_t* loop) {  if (loop->stop_flag != 0)    return 0;  if (!uv__has_active_handles(loop) && !uv__has_active_reqs(loop))    return 0;  if (!QUEUE_EMPTY(&loop->idle_handles))    return 0;  if (!QUEUE_EMPTY(&loop->pending_queue))    return 0;  if (loop->closing_handles)    return 0;  return uv__next_timeout(loop);
}

int uv__next_timeout(const uv_loop_t* loop) {  const struct heap_node* heap_node;  const uv_timer_t* handle;
  uint64_t diff;
  heap_node = heap_min((const struct heap*) &loop->timer_heap);  if (heap_node == NULL)    return -1; /* block indefinitely */
  handle = container_of(heap_node, uv_timer_t, heap_node);  if (handle->timeout time)    return 0;//这句代码给出了关键性的指导
  diff = handle->timeout - loop->time;//不能大于最大的INT_MAX
  if (diff > INT_MAX)
    diff = INT_MAX;  return diff;
}