HttpUrlConnection - locked <0x2871d648> (a java.io.BufferedInputStream)

请问下各位 我用java自带的 HttpUrlConnection
用jstack导出信息发现有死锁
conn.getHeaderFields().get("Set-Cookie")
getHeader 也会有锁 这是神马情况?
导出的信息里面有很多这样的死锁线程"Thread-421" prio=6 tid=0x08ae4400 nid=0x1540 runnable [0x065cf000]
   java.lang.Thread.State: RUNNABLE
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.read(SocketInputStream.java:129)
at java.io.BufferedInputStream.fill(BufferedInputStream.java:218)
at java.io.BufferedInputStream.read1(BufferedInputStream.java:258)
at java.io.BufferedInputStream.read(BufferedInputStream.java:317)
- locked <0x2871d648> (a java.io.BufferedInputStream)
at sun.net.www.http.HttpClient.parseHTTPHeader(HttpClient.java:698)
at sun.net.www.http.HttpClient.parseHTTP(HttpClient.java:641)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1218)
- locked <0x2871d680> (a sun.net.www.protocol.http.HttpURLConnection)
at sun.net.www.protocol.http.HttpURLConnection.getHeaderFields(HttpURLConnection.java:2362)
at com.horn.util.MsgManage.sendHttpMessage(MsgManage.java:1003)
at com.horn.util.MsgManage.sendHttpMessage(MsgManage.java:954)
at com.horn.util.PollMessageThread.run(PollMessageThread.java:63)   Locked ownable synchronizers:
- NoneHttpUrlConnection