java.net.SocketException: Socket Closed 即使输入和输出流在读、写后关闭

Question

我正在运行多线程 Java 应用程序，其中以下方法将由许多线程（大约 300 个）并行执行。我只在线程数更多而不是线程数小于 50 时才看到此异常。 我在 stackoverflow 中阅读了几篇文章，并且代码看起来对所描述的帖子的抱怨。任何帮助，将不胜感激。提前致谢。

这是我的方法：

public static String invokeWebService(String request, String fwfmId, BatchVO batchVO){
    String responseString = "";
    //log the request string
    Logger_trace.info("Service request for input "+ fwfmId +":: "+CommonUtil.removeCrLf(request));
    try {
            URL url = new URL(batchVO.getWebServiceUrl());
            HttpURLConnection  urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("POST");
            urlConnection.setRequestProperty("Content-type", "text/xml; charset=utf-8");

            urlConnection.setDoOutput(true);
            urlConnection.setDoInput(true);
            urlConnection.setConnectTimeout(Integer.parseInt(batchVO.getConnectionTimeOut()));
            urlConnection.setReadTimeout(Integer.parseInt(batchVO.getReadTimeOut()));
            OutputStream outputStream = urlConnection.getOutputStream();
            outputStream.write(request.getBytes());
            outputStream.flush();

            //get response form input stream and convert into string
            InputStreamReader inputStreamReader = new InputStreamReader(urlConnection.getInputStream());
            BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
            String inputLine;
            StringBuffer response = new StringBuffer();

            while ((inputLine = bufferedReader.readLine()) != null) {
                response.append(inputLine);
            }

            responseString = response.toString();

            //close resources
            bufferedReader.close();
            inputStreamReader.close();
            outputStream.close(); 

            //log the response string
            logger_trace.info("Service response for input "+ fwfmId +":: "+ CommonUtil.removeCrLf(responseString));

            //Update Database columns
            updateRecordInTable(request, responseString, fwfmId, batchVO.getDataSource(), batchVO.getBatchId());    

        } catch (SocketConnectException e) {
            logger_trace.error("WebserviceHandler.invokeWebService : SocketConnectException block : "+fwfmId +" ", e);
            updateRecordInTableWithTimeout(fwfmId, batchVO.getDataSource(), batchVO.getBatchId());
        } catch (SocketTimeoutException e) {
            logger_trace.error("WebserviceHandler.invokeWebService : SocketTimeoutException block : "+ fwfmId+" ", e);
            updateRecordInTableWithTimeout(fwfmId, batchVO.getDataSource(), batchVO.getBatchId());
        } catch (MalformedURLException e) {
            logger_trace.error("WebserviceHandler.invokeWebService : MalformedURLException block : ", e);
        } catch (IOException e) {
            logger_trace.error("WebserviceHandler.invokeWebService : IOException block : ", e);
        } catch(Exception e){
            logger_trace.error("WebserviceHandler.invokeWebService : General Exception block : ", e);
        }
        return responseString;
    }

例外：

 [ERROR] 2017-10-31 03:18:54,435 [main] TRACE -
 WebserviceHandler.invokeWebService : IOException block : 
 java.net.SocketException: Socket Closed
         at java.net.AbstractPlainSocketImpl.setOption(AbstractPlainSocketImpl.java:212)
 ~[?:1.8.0_131]
         at java.net.Socket.setTcpNoDelay(Socket.java:980) ~[?:1.8.0_131]
         at weblogic.net.http.HttpClient.openServer(HttpClient.java:411)
 ~[wlfullclient.jar:12.2.2.0.0]
         at weblogic.net.http.HttpClient.openServer(HttpClient.java:511)
 ~[wlfullclient.jar:12.2.2.0.0]
         at weblogic.net.http.HttpClient.New(HttpClient.java:313) ~[wlfullclient.jar:12.2.2.0.0]
         at weblogic.net.http.HttpURLConnection.getHttpClient(HttpURLConnection.java:314)
 ~[wlfullclient.jar:12.2.2.0.0]
         at weblogic.net.http.HttpURLConnection.getInputStream(HttpURLConnection.java:760)
 ~[wlfullclient.jar:12.2.2.0.0]
         at weblogic.net.http.SOAPHttpURLConnection.getInputStream(SOAPHttpURLConnection.java:41)
 ~[wlfullclient.jar:12.2.2.0.0]
         at ca.bell.webservice.WebServiceHandler.invokeWebService(WebServiceHandler.java:56)
 [MigrationTool.jar:?]
         at ca.bell.webservice.ExecuteMigrationWork.performRun(ExecuteMigrationWork.java:40)
 [MigrationTool.jar:?]
         at ca.bell.workmanagement.work.Work.call(Work.java:155) [MigrationTool.jar:?]
         at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_131]
         at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
 [?:1.8.0_131]
         at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
 [?:1.8.0_131]
         at java.lang.Thread.run(Thread.java:748) [?:1.8.0_131]

Answer 1

有趣。让我们从最近的异常源开始分析您的堆栈跟踪。从AbstractPlainSocketImpl 的source code 开始，强制执行的第一个前提条件是：

public void setOption(int opt, Object val) throws SocketException {
  if (isClosedOrPending()) {
    throw new SocketException("Socket Closed");
  }
...

由于您的HttpURLConnection 的范围仅限于方法invokeWebService，我们可以排除套接字上的并发操作的假设，并且由于看起来不错的方法并且没有关闭套接字，我相信isClosedOrPending 返回 true 因为套接字的文件描述符是 null:

public boolean isClosedOrPending() {
    /*
     * Lock on fdLock to ensure that we wait if a
     * close is in progress.
     */
    synchronized (fdLock) {
        if (closePending || (fd == null)) {
            return true;
        } else {
            return false;
        }
    }
}

这个分析中有问题的是为什么fd 文件描述符是null。然而，这在现阶段并不重要。如果我们相信我们的假设，我们可以得出的一个结论是，您正在为您的系统创建过多的连接来处理。

我们如何解决这个问题？这里我们需要退后一步，看看是否可以重构代码来限制并发连接数。我需要有关您的具体实现的更多详细信息，以缩小原本无限的设计候选范围。例如，连接池是否合适？我们应该实施背压并限制客户端吗？我们应该水平扩展并分配负载吗？