java为什么这个文件上传线程（ServletFileUpload.parseRequest）被阻止？

Question

我们正在WildFly 12和Java 8上运行一个web应用程序。以下线程被锁定，导致应用程序无响应 org.apache.commons.fileupload.servlet.ServletFileUpload.parseRequest

netstat输出显示许多线程处于CLOSE-WAIT状态

以下是堆栈跟踪：

 threadId:0x000000002526d000 - nativeId:0x1770 - nativeId (decimal):6000 - state:RUNNABLE
stackTrace:
java.lang.Thread.State: RUNNABLE
at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method)
at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(WindowsSelectorImpl.java:296)
at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(WindowsSelectorImpl.java:278)
at sun.nio.ch.WindowsSelectorImpl.doSelect(WindowsSelectorImpl.java:159)
at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
- locked <0x00000006eae8c4e0> (a sun.nio.ch.Util$3)
- locked <0x00000006eae8c4d0> (a java.util.Collections$UnmodifiableSet)
- locked <0x00000006eae8c270> (a sun.nio.ch.WindowsSelectorImpl)
at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:101)
at org.xnio.nio.SelectorUtils.await(SelectorUtils.java:51)
at org.xnio.nio.NioSocketConduit.awaitReadable(NioSocketConduit.java:358)
at org.xnio.conduits.AbstractSourceConduit.awaitReadable(AbstractSourceConduit.java:66)
at io.undertow.conduits.ReadDataStreamSourceConduit.awaitReadable(ReadDataStreamSourceConduit.java:101)
at io.undertow.conduits.FixedLengthStreamSourceConduit.awaitReadable(FixedLengthStreamSourceConduit.java:285)
at org.xnio.conduits.ConduitStreamSourceChannel.awaitReadable(ConduitStreamSourceChannel.java:151)
at io.undertow.channels.DetachableStreamSourceChannel.awaitReadable(DetachableStreamSourceChannel.java:77)
at io.undertow.server.HttpServerExchange$ReadDispatchChannel.awaitReadable(HttpServerExchange.java:2197)
at org.xnio.channels.Channels.readBlocking(Channels.java:295)
at io.undertow.servlet.spec.ServletInputStreamImpl.readIntoBuffer(ServletInputStreamImpl.java:192)
at io.undertow.servlet.spec.ServletInputStreamImpl.read(ServletInputStreamImpl.java:168)
at org.apache.commons.fileupload.MultipartStream$ItemInputStream.makeAvailable(MultipartStream.java:999)
at org.apache.commons.fileupload.MultipartStream$ItemInputStream.read(MultipartStream.java:903)
at java.io.InputStream.read(InputStream.java:101)
at org.apache.commons.fileupload.util.Streams.copy(Streams.java:100)
at org.apache.commons.fileupload.util.Streams.copy(Streams.java:70)
at org.apache.commons.fileupload.FileUploadBase.parseRequest(FileUploadBase.java:347)
at org.apache.commons.fileupload.servlet.ServletFileUpload.parseRequest(ServletFileUpload.java:115)
at com.servicedesk.UploadFile.doPost(UploadFile.java:151)


threadId:0x000000002757d800 - nativeId:0x1934 - nativeId (decimal):6452 - state:BLOCKED
stackTrace:
java.lang.Thread.State: BLOCKED (on object monitor)
at com.servicedesk.UploadFile.doPost(UploadFile.java:45)
- waiting to lock <0x00000006ec077030> (a com.servicedesk.UploadFile)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:707)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:74)
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:129)
at urlfilter.SQLInjectionFilter.doFilter(SQLInjectionFilter.java:147)
at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:317)

用于上载文件的Java代码：

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

public class UploadFile extends HttpServlet {
    synchronized protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            File f=new File(fileDestination);
            boolean exits=f.exists();
            if(!exits)
            {
             new File(fileDestination).mkdir();
            }
            DiskFileItemFactory  fileItemFactory = new DiskFileItemFactory ();       
            ServletFileUpload uploadHandler = new ServletFileUpload(fileItemFactory);
            List items = uploadHandler.parseRequest(request);          
            Iterator iterator = items.iterator();
            while(iterator.hasNext()) {
                FileItem item = (FileItem) iterator.next();                
                // Some business logic               
            }
    }
}