#fixed code
                                public void releaseConnection(ManagedClientConnection conn, long validDuration, TimeUnit timeUnit) {

        if (!(conn instanceof BasicPooledConnAdapter)) {
            throw new IllegalArgumentException
                ("Connection class mismatch, " +
                 "connection not obtained from this manager.");
        }
        BasicPooledConnAdapter hca = (BasicPooledConnAdapter) conn;
        if ((hca.getPoolEntry() != null) && (hca.getManager() != this)) {
            throw new IllegalArgumentException
                ("Connection not obtained from this manager.");
        }
        synchronized (hca) {
            BasicPoolEntry entry = (BasicPoolEntry) hca.getPoolEntry();
            if (entry == null) {
                return;
            }
            try {
                // make sure that the response has been read completely
                if (hca.isOpen() && !hca.isMarkedReusable()) {
                    // In MTHCM, there would be a call to
                    // SimpleHttpConnectionManager.finishLastResponse(conn);
                    // Consuming the response is handled outside in 4.0.

                    // make sure this connection will not be re-used
                    // Shut down rather than close, we might have gotten here
                    // because of a shutdown trigger.
                    // Shutdown of the adapter also clears the tracked route.
                    hca.shutdown();
                }
            } catch (IOException iox) {
                if (log.isDebugEnabled())
                    log.debug("Exception shutting down released connection.",
                              iox);
            } finally {
                boolean reusable = hca.isMarkedReusable();
                if (log.isDebugEnabled()) {
                    if (reusable) {
                        log.debug("Released connection is reusable.");
                    } else {
                        log.debug("Released connection is not reusable.");
                    }
                }
                hca.detach();
                pool.freeEntry(entry, reusable, validDuration, timeUnit);
            }
        }
    }
#vulnerable code 
                                public void releaseConnection(ManagedClientConnection conn, long validDuration, TimeUnit timeUnit) {

        if (!(conn instanceof BasicPooledConnAdapter)) {
            throw new IllegalArgumentException
                ("Connection class mismatch, " +
                 "connection not obtained from this manager.");
        }
        BasicPooledConnAdapter hca = (BasicPooledConnAdapter) conn;
        if ((hca.getPoolEntry() != null) && (hca.getManager() != this)) {
            throw new IllegalArgumentException
                ("Connection not obtained from this manager.");
        }

        try {
            // make sure that the response has been read completely
            if (hca.isOpen() && !hca.isMarkedReusable()) {
                // In MTHCM, there would be a call to
                // SimpleHttpConnectionManager.finishLastResponse(conn);
                // Consuming the response is handled outside in 4.0.

                // make sure this connection will not be re-used
                // Shut down rather than close, we might have gotten here
                // because of a shutdown trigger.
                // Shutdown of the adapter also clears the tracked route.
                hca.shutdown();
            }
        } catch (IOException iox) {
            //@@@ log as warning? let pass?
            if (log.isDebugEnabled())
                log.debug("Exception shutting down released connection.",
                          iox);
        } finally {
            BasicPoolEntry entry = (BasicPoolEntry) hca.getPoolEntry();
            boolean reusable = hca.isMarkedReusable();
            if (log.isDebugEnabled()) {
                if (reusable) {
                    log.debug("Released connection is reusable.");
                } else {
                    log.debug("Released connection is not reusable.");
                }
            }
            hca.detach();
            if (entry != null) {
                pool.freeEntry(entry, reusable, validDuration, timeUnit);
            }
        }
    } 
                            #location 37 
                            #vulnerability type INTERFACE_NOT_THREAD_SAFE