• I have searched the issues of this repository and believe that this is not a duplicate.
• I have checked the FAQ of this repository and believe that this is not a duplicate.

Environment

• Dubbo version: 2.6.5
• Operating System version: Red Hat 4.8.5-11
• Java version:1.8.0

Steps to reproduce this issue

1. consumer use http protocol
2. submit a POST request

Pls. provide [GitHub address] to reproduce this issue.

Expected Result

response data

Actual Result

report errors

java.util.concurrent.ExecutionException: java.lang.IllegalStateException: Invalid use of BasicClientConnManager: connection still allocated.
Make sure to release the connection before allocating another one.
	at java.util.concurrent.FutureTask.report(FutureTask.java:122) ~[?:1.8.0]
	at java.util.concurrent.FutureTask.get(FutureTask.java:192) ~[?:1.8.0]
	at