ResponseListener 在 snmp4j 中如何工作

Question

我编写了一个简单的程序来了解 snmp4j 异步请求/响应的工作原理：

TransportMapping transport = new DefaultUdpTransportMapping();
Snmp snmp = new Snmp(transport);
transport.listen();

Address targetAddress = GenericAddress.parse("udp:192.168.1.116/161");
CommunityTarget target = new CommunityTarget();
target.setAddress(targetAddress);
target.setCommunity(new OctetString("nid"));
target.setRetries(0);
target.setTimeout(30000);
target.setVersion(SnmpConstants.version2c);

ResponseListener listener = new ResponseListener() {
    @Override
    public void onResponse(ResponseEvent event) {
        ((Snmp) event.getSource()).cancel(event.getRequest(), this);
        System.out.println("Received response PDU is: " + event.getResponse());
        System.out.println("response listener thread id: " + Thread.currentThread().getId());
        System.out.println("**********************************");
        try {
            Thread.sleep(5000);
        } catch (InterruptedException ex) {
            Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
};

System.out.println("main thread id: " + Thread.currentThread().getId());
for (int i = 0; i < 10; i++) {
    PDU pdu1 = new PDU();
    pdu1.add(new VariableBinding(new OID("1.3.6.1.4.1.22420.2.5.3.1.1.1")));
    pdu1.add(new VariableBinding(new OID("1.3.6.1.4.1.22420.2.5.3.1.1.2")));
    pdu1.setType(PDU.GET);
    snmp.send(pdu1, target, null, listener);
}

Thread.sleep(100000); 

示例输出如下：

main thread id: 1
Received response PDU is: RESPONSE[requestID=205585942, errorStatus=Success(0), errorIndex=0, VBS[1.3.6.1.4.1.22420.2.5.3.1.1.1 = 1; 1.3.6.1.4.1.22420.2.5.3.1.1.2 = 2]]
response listener thread id: 8
**********************************
Received response PDU is: RESPONSE[requestID=205585943, errorStatus=Success(0), errorIndex=0, VBS[1.3.6.1.4.1.22420.2.5.3.1.1.1 = 1; 1.3.6.1.4.1.22420.2.5.3.1.1.2 = 2]]
response listener thread id: 8
**********************************
Received response PDU is: RESPONSE[requestID=205585944, errorStatus=Success(0), errorIndex=0, VBS[1.3.6.1.4.1.22420.2.5.3.1.1.1 = 1; 1.3.6.1.4.1.22420.2.5.3.1.1.2 = 2]]
response listener thread id: 8
**********************************
Received response PDU is: RESPONSE[requestID=205585945, errorStatus=Success(0), errorIndex=0, VBS[1.3.6.1.4.1.22420.2.5.3.1.1.1 = 1; 1.3.6.1.4.1.22420.2.5.3.1.1.2 = 2]]
response listener thread id: 8
**********************************
Received response PDU is: RESPONSE[requestID=205585946, errorStatus=Success(0), errorIndex=0, VBS[1.3.6.1.4.1.22420.2.5.3.1.1.1 = 1; 1.3.6.1.4.1.22420.2.5.3.1.1.2 = 2]]
response listener thread id: 8
**********************************
Received response PDU is: RESPONSE[requestID=205585947, errorStatus=Success(0), errorIndex=0, VBS[1.3.6.1.4.1.22420.2.5.3.1.1.1 = 1; 1.3.6.1.4.1.22420.2.5.3.1.1.2 = 2]]
response listener thread id: 8
**********************************
Received response PDU is: null
response listener thread id: 9
**********************************
Received response PDU is: RESPONSE[requestID=205585948, errorStatus=Success(0), errorIndex=0, VBS[1.3.6.1.4.1.22420.2.5.3.1.1.1 = 1; 1.3.6.1.4.1.22420.2.5.3.1.1.2 = 2]]
response listener thread id: 8
**********************************
Received response PDU is: null
response listener thread id: 9
**********************************
Received response PDU is: RESPONSE[requestID=205585950, errorStatus=Success(0), errorIndex=0, VBS[1.3.6.1.4.1.22420.2.5.3.1.1.1 = 1; 1.3.6.1.4.1.22420.2.5.3.1.1.2 = 2]]
response listener thread id: 8
**********************************

输出显示多个线程 ID。这意味着响应数据包是并行处理的。我对吗？线程 id 9 的两个响应返回null。有什么理由吗？使用同步模型时我不明白。难道这是因为Thread.sleep里面ResponseListener。因此，如果我不能在内部进行阻塞工作ResponseListener并且我想并行处理响应，我需要添加ExecuterService?

Answer 1

SNMP4j 在内部使用线程池来处理消息。sResponseListener是onResponse()从您看到的线程 ID 的那些线程中调用的。与同步模式不同的是，它是在您自己的线程中执行的。

返回null值表示超时完成。是的，我猜这是因为您在 中休眠了 5 秒ResponseListener，这会阻塞消息接收线程之一。

至于ExecutorService，将处理负载从 SNMP4j 消息线程移至您自己的代码中是一个好主意，您可以在其中控制队列等。或者，您可以使用同步List和计数Semaphore来唤醒线程处理收到的消息。