#fixed code
                                public void releaseConnection(final ManagedClientConnection conn, long keepalive, TimeUnit tunit) {
        if (!(conn instanceof ManagedClientConnectionImpl)) {
            throw new IllegalArgumentException("Connection class mismatch, " +
                 "connection not obtained from this manager");
        }
        ManagedClientConnectionImpl managedConn = (ManagedClientConnectionImpl) conn;
        synchronized (managedConn) {
            if (this.log.isDebugEnabled()) {
                this.log.debug("Releasing connection " + conn);
            }
            if (managedConn.getPoolEntry() == null) {
                return; // already released
            }
            ClientConnectionManager manager = managedConn.getManager();
            if (manager != null && manager != this) {
                throw new IllegalStateException("Connection not obtained from this manager");
            }
            synchronized (this) {
                if (this.shutdown) {
                    shutdownConnection(managedConn);
                    return;
                }
                try {
                    if (managedConn.isOpen() && !managedConn.isMarkedReusable()) {
                        shutdownConnection(managedConn);
                    }
                    this.poolEntry.updateExpiry(keepalive, tunit != null ? tunit : TimeUnit.MILLISECONDS);
                    if (this.log.isDebugEnabled()) {
                        String s;
                        if (keepalive > 0) {
                            s = "for " + keepalive + " " + tunit;
                        } else {
                            s = "indefinitely";
                        }
                        this.log.debug("Connection can be kept alive " + s);
                    }
                } finally {
                    managedConn.detach();
                    this.conn = null;
                    if (this.poolEntry.isClosed()) {
                        this.poolEntry = null;
                    }
                }
            }
        }
    }
#vulnerable code 
                                public void releaseConnection(final ManagedClientConnection conn, long keepalive, TimeUnit tunit) {
        assertNotShutdown();
        if (!(conn instanceof ManagedClientConnectionImpl)) {
            throw new IllegalArgumentException("Connection class mismatch, " +
                 "connection not obtained from this manager");
        }
        if (this.log.isDebugEnabled()) {
            this.log.debug("Releasing connection " + conn);
        }
        ManagedClientConnectionImpl managedConn = (ManagedClientConnectionImpl) conn;
        synchronized (managedConn) {
            if (managedConn.getPoolEntry() == null) {
                return; // already released
            }
            ClientConnectionManager manager = managedConn.getManager();
            if (manager != null && manager != this) {
                throw new IllegalStateException("Connection not obtained from this manager");
            }
            synchronized (this) {
                try {
                    if (managedConn.isOpen() && !managedConn.isMarkedReusable()) {
                        try {
                            managedConn.shutdown();
                        } catch (IOException iox) {
                            if (this.log.isDebugEnabled()) {
                                this.log.debug("I/O exception shutting down released connection", iox);
                            }
                        }
                    }
                    this.poolEntry.updateExpiry(keepalive, tunit != null ? tunit : TimeUnit.MILLISECONDS);
                    if (this.log.isDebugEnabled()) {
                        String s;
                        if (keepalive > 0) {
                            s = "for " + keepalive + " " + tunit;
                        } else {
                            s = "indefinitely";
                        }
                        this.log.debug("Connection can be kept alive " + s);
                    }
                } finally {
                    managedConn.detach();
                    this.conn = null;
                    if (this.poolEntry.isClosed()) {
                        this.poolEntry = null;
                    }
                }
            }
        }
    } 
                            #location 8 
                            #vulnerability type INTERFACE_NOT_THREAD_SAFE