tornado版本及多线程情况梳理

1.  python2.6  tornado-4.2-py26环境

2. import tornado.ioloop
   import tornado.web
   from tornado.web import asynchronous
   from concurrent import futures 
   executor = futures.ThreadPoolExecutor(max_workers=2)
   
   def call(handler):
       handler.write("Hello, World!")
       handler.finish() # 如果不写这行则回挂住
   
   class MainHandler(tornado.web.RequestHandler):
       
       @asynchronous
       def get(self):
           executor.submit(call, self)
   
   def make_app():
       return tornado.web.Application([
           (r"/", MainHandler),
       ])  
   
   if __name__ == "__main__":
       app = make_app()
       app.listen(9090)
       tornado.ioloop.IOLoop.current().start()
   ~                                             

   
   如果get/post返回future/gen（异步, yield的生成器）, 则需申明asynchronous, 不然该future不会加入IOLoop的事件, 直接处理完成, 如果在线程/协程中再有finish调用, 则会出现finish() called twice, 下面会详细说到。反过来说如果申明是asynchronous, 必需返回future 或者 gen 
3. finish() call twice 示例代码：需注意线程抛的异常，主线程是catch不到的

4. import tornado.ioloop
   import tornado.web
   from tornado.web import asynchronous
   from concurrent import futures 
   executor = futures.ThreadPoolExecutor(max_workers=2)
   import time
   import traceback
   
   def call(handler):
       try:
            print id(handler)
            handler.write("Hello, World! id: %s" % id(handler))
            time.sleep(5)
            handler.finish()
            print "over.id[%s]" % id(handler)
       except:
           print traceback.format_exc()
   
   class MainHandler(tornado.web.RequestHandler):
       
       #@asynchronous
       def get(self):
           executor.submit(call, self)
   
   def make_app():
       return tornado.web.Application([
           (r"/", MainHandler),
       ])  
   
   if __name__ == "__main__":
       app = make_app()
       app.listen(9090)
       tornado.ioloop.IOLoop.current().start()

5. 另外注意如果使用tornado.ioloop.IOLoop.instance().add_callback(lambda: handler.finish({"xx": "yy"}))  返回值最好是字符串, 编码如果出现问题，则用户不会调用到finish，源码如下：

6.     def write(self, chunk):
           
           if self._finished:
               raise RuntimeError("Cannot write() after finish()")
           if not isinstance(chunk, (bytes, unicode_type, dict)):
               message = "write() only accepts bytes, unicode, and dict objects"
               if isinstance(chunk, list):
                   message += ". Lists not accepted for security reasons; see http://www.tornadoweb.org/en/stable/web.html#tornado.web.RequestHandler.write"
               raise TypeError(message)
           if isinstance(chunk, dict):
               chunk = escape.json_encode(chunk)  # 这里会报 'utf8' codec can't decode bytes
               self.set_header("Content-Type", "application/json; charset=UTF-8")
           chunk = utf8(chunk)
           self._write_buffer.append(chunk)