Question

Hello Erlangers先生：）

另一位Erlang爱好者在这里玩这种语言。我有一个非常简单的YAWS应用程序模块，当单个客户端访问时它可以正常工作。但是，如果我尝试跨多个客户端来模拟轻量级流量，那些客户端就会开始收到错误。知道是什么导致它吗？

产生客户的代码：

-module(concurrent).
-export([measure/0, get/0]).

get() ->
  Result = httpc:request("http://localhost:8080/blah"),
  io:format("Result: ~p.\n", [Result]).

get_spawner(0) -> io:format("Done.\n");
get_spawner(Times) ->
  spawn(concurrent, get, []),
  get_spawner(Times - 1).

measure() ->
  io:fwrite("Starting inets...\n"),
  inets:start(),
  io:fwrite("Done\n"),

  io:fwrite("Creating blah...\n"),
  httpc:request(put, { "http://localhost:8080/blah", [], "", "" }, [], []),
  io:fwrite("Done\n"),

  get_spawner(9),

  io:fwrite("Stopping inets...\n"),
  inets:stop(),
  io:fwrite("Done\n"),

  init:stop().

我观察到它对8个并发客户端一切正常，但当我跨越9个或更多客户端时，它们开始从服务器接收以下消息：

=ERROR REPORT==== 24-Jan-2017::12:30:04 ===
** Generic server httpc_manager terminating
** Last message in was {request,
                           {request,undefined,<0.74.0>,0,http,
                               {"localhost",8080},
                               "/blah",[],get,
                               {http_request_h,undefined,"keep-alive",
                                   undefined,undefined,undefined,undefined,
                                   undefined,undefined,undefined,undefined,
                                   undefined,undefined,undefined,undefined,
                                   undefined,undefined,"localhost:8080",
                                   undefined,undefined,undefined,undefined,
                                   undefined,undefined,undefined,undefined,
                                   undefined,[],undefined,undefined,undefined,
                                   undefined,"0",undefined,undefined,
                                   undefined,undefined,undefined,undefined,[]},
                               {[],[]},
                               {http_options,"HTTP/1.1",infinity,true,
                                   {essl,[]},
                                   undefined,false,infinity,false},
                               "http://localhost:8080/blah",[],none,[],
                               1485261004189,undefined,undefined,false}}
** When Server state == {state,[],httpc_manager__handler_db,
                            {cookie_db,undefined,8209},
                            httpc_manager__session_db,httpc_manager,
                            {options,
                                {undefined,[]},
                                {undefined,[]},
                                0,2,5,120000,2,disabled,false,inet,default,
                                default,[]}}
** Reason for termination ==
** {'EXIT',
       {shutdown,
           {gen_server,call,
               [httpc_handler_sup,
                {start_child,
                    [<0.61.0>,
                     {request,#Ref<0.0.6.64>,<0.74.0>,0,http,
                         {"localhost",8080},
                         "/blah",[],get,
                         {http_request_h,undefined,"keep-alive",undefined,
                             undefined,undefined,undefined,undefined,
                             undefined,undefined,undefined,undefined,
                             undefined,undefined,undefined,undefined,
                             undefined,"localhost:8080",undefined,undefined,
                             undefined,undefined,undefined,undefined,
                             undefined,undefined,undefined,[],undefined,
                             undefined,undefined,undefined,"0",undefined,
                             undefined,undefined,undefined,undefined,
                             undefined,[]},
                         {[],[]},
                         {http_options,"HTTP/1.1",infinity,true,
                             {essl,[]},
                             undefined,false,infinity,false},
                         "http://localhost:8080/blah",[],none,[],
                         1485261004189,undefined,undefined,false},
                     {options,
                         {undefined,[]},
                         {undefined,[]},
                         0,2,5,120000,2,disabled,false,inet,default,default,
                         []},
                     httpc_manager]},
                infinity]}}}

=ERROR REPORT==== 24-Jan-2017::12:30:04 ===
Error in process <0.74.0> with exit value:
{{case_clause,
     {undefined,
         {error,
             {'EXIT',
                 {shutdown,
                     {gen_server,call,
                         [httpc_handler_sup,
                          {start_child,
                              [<0.61.0>,
                               {request,#Ref<0.0.6.64>,<0.74.0>,0,http,
                                   {"localhost",8080},
                                   "/blah",[],get,
                                   {http_request_h,undefined,"keep-alive",
                                       undefined,undefined,undefined,
                                       undefined,undefined,undefined,
                                       undefined,undefined,undefined,
                                       undefined,undefined,undefined,
                                       undefined,undefined,"localhost:8080",
                                       undefined,undefined,undefined,
                                       undefined,undefined,undefined,
                                       undefined,undefined,undefined,[],
                                       undefined,undefined,undefined,
                                       undefined,"0",undefined,undefined,
                                       undefined,undefined,undefined,
                                       undefined,[]},
                                   {[],[]},
                                   {http_options,"HTTP/1.1",infinity,true,
                                       {essl,[]},
                                       undefined,false,infinity,false},
                                   "http://localhost:8080/blah",[],none,[],
                                   1485261004189,undefined,undefined,false},
                               {options,
                                   {undefined,[]},
                                   {undefined,[]},
                                   0,2,5,120000,2,disabled,false,inet,default,
                                   default,[]},
                               httpc_manager]},
                          infinity]}}}}}},
 [{httpc,handle_request,9,[{file,"httpc.erl"},{line,574}]},
  {concurrent,get,0,
      [{file,
           "c:/Users/piotr_justyna/Documents/rets/performance_tests/concurrent.erl"},
       {line,5}]}]}

在服务器端，我得到了这个：

=ERROR REPORT==== 24-Jan-2017::12:28:55 ===
Unhandled reply fr. do_recv() {error,econnaborted}

我确信这是直截了当的，只是无法弄清楚它是什么。它是导致它的并发连接数吗？你能帮助更多地了解这个吗？

此致彼得

Answer 1

您的代码会产生多个httpc:request/1来电，但之后会立即停止inets：

...
get_spawner(9),
io:fwrite("Stopping inets...\n"),
inets:stop(),
...

由于inets已关闭，正在进行的请求会过早关闭，如错误报告中所示：

** Reason for termination ==
** {'EXIT',
       {shutdown,
           {gen_server,call,
               [httpc_handler_sup,

在调用inets:stop/0之前，您需要让所有生成的请求的父级等待这些请求完成。一种方法是将父pid传递给每个生成的子节点，并且httpc:request/1返回后，让子节点向父节点发送消息。父母将产生所有N个孩子，然后坐在循环中等待接收来自孩子的N完成消息，并且只有在收到所有完成消息后才会调用inets:stop/0。

它适用于8个请求而不是9个请求的原因是由于在调用inets:stop/0之前缺少等待的竞争条件。请求处理接受器进程的Yaws池的默认大小恰好为8.当您的代码发送8个请求时，池会快速处理它以超过您的代码对inets:stop/0的调用，但是对于9，当一个接受者处理两个请求时，会有轻微的延迟，并且轻微的时间更改足以让您inets:stop/0调用一个或多个客户端进程。您可以通过acceptor_pool_size配置变量修改Yaws接受器池大小。

如果您对负载测试非常认真，可以考虑使用像tsung这样的工业级解决方案，而不是自己动手。

YAWS在轻负载下响应错误。 “未处理的回复fr.do_recv（）{error，econnaborted}”

1 个答案: