Linux下学习用C语言实现MQTT(三）（异步函数）
客户端库支持两种操作模式，称为同步模式和异步模式。如果你的应用程序调用了MQTTClient_setCallbacks()，则客户端将会进入异步模式，否则会以同步模式运行。
同步模式下，客户端应用程序运行在单个线程上。信息的发布使用MQTTClient_publish()和MQTTClient_publishMessage()函数。为了确定Qos1和Qos2（详见Quality of service）的信息已经成功传递，应用程序必须调用MQTTClient_waitForCompletion()这个函数。一个展示同步发布的例子可查看Synchronous publication example。同步模式下接收信息使用 MQTTClient_receive()函数，客户端应用程序必须相对频繁地调用 MQTTClient_receive()或MQTTClient_yield()，以便允许（执行）确认和保持与服务器的网络连接的 MQTT "ping"这些操作。
异步模式下，客户端应用程序运行在若干个线程上。如同同步模式，（异步模式中）主程序调用客户端库中的函数来发布和订阅，而在在后台进行握手和维持网络连接这些操作。客户端应用程序通过调用 MQTTClient_setCallbacks()( (详情请见MQTTClient_messageArrived(), MQTTClient_connectionLost()和 MQTTClient_deliveryComplete()))来使用库进行回调注册而获得状态通知和消息接收。然而, 这个 API 不是线程安全的-不可能从多个线程调用它而不进行同步。你可以使用MQTTAsync API来完成此操作。
接下使用MQTTAsync系列函数来实现publish和subscribe:
publish端：
#include subscribe端：
#include to quit\n\n" , TOPIC, CLIENTID, QOS);
opts.onSuccess = onSubscribe;
opts.onFailure = onSubscribeFailure;
opts.context = client;
deliveredtoken = 0;
if ((rc = MQTTAsync_subscribe(client, TOPIC, QOS, &opts)) != MQTTASYNC_SUCCESS)
{
printf("Failed to start subscribe, return code %d\n", rc);
exit(EXIT_FAILURE);
}
}
int main(int argc, char* argv[])
{
MQTTAsync client;
MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
MQTTAsync_disconnectOptions disc_opts = MQTTAsync_disconnectOptions_initializer;
int rc;
int ch;
MQTTAsync_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);
MQTTAsync_setCallbacks(client, client, connlost, msgarrvd, NULL);
conn_opts.keepAliveInterval = 20;
conn_opts.cleansession = 1;
conn_opts.onSuccess = onConnect;
conn_opts.onFailure = onConnectFailure;
conn_opts.context = client;
if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS)
{
printf("Failed to start connect, return code %d\n", rc);
exit(EXIT_FAILURE);
}
while (!subscribed)
#if defined(WIN32)
Sleep(100);
#else
usleep(10000L);
#endif
if (finished)
goto exit;
do
{
ch = getchar();
} while (ch!='Q' && ch != 'q');
disc_opts.onSuccess = onDisconnect;
if ((rc = MQTTAsync_disconnect(client, &disc_opts)) != MQTTASYNC_SUCCESS)
{
printf("Failed to start disconnect, return code %d\n", rc);
exit(EXIT_FAILURE);
}
while (!disc_finished)
#if defined(WIN32)
Sleep(100);
#else
usleep(10000L);
#endif
exit:
MQTTAsync_destroy(&client);
return rc;
}
编译同样要加上头文件，动态库，运行时可能也需要导入环境变量。
zhanghang@Ubuntu-14:~/MQTT/paho.mqtt.c/build/output/samples$ ./MQTTAsync_publish
Waiting for publication of Hello World!
on topic MQTT Examples for client with ClientID: ExampleClientPub
Successful connection
Message with token value 1 delivery confirmed
Successful disconnection
zhanghang@Ubuntu-14:~/MQTT/paho.mqtt.c/build/output/samples$ ./MQTTAsync_subscribe
Successful connection
Subscribing to topic MQTT Examples
for client ExampleClientSub using QoS1
Press Q to quit
Subscribe succeeded
Message arrived
topic: MQTT Examples
message: Hello World!
客户端成功推送话题和订阅话题。
使用mosquitto分别测试publish和subscribe成功
zhanghang@Ubuntu-14:~/MQTT/paho.mqtt.c/build/output/samples$ ./MQTTAsync_publish
Waiting for publication of Hello World!
on topic MQTT Examples for client with ClientID: ExampleClientPub
Successful connection
Message with token value 1 delivery confirmed
Successful disconnection
zhanghang@Ubuntu-14:~/MQTT/paho.mqtt.c/build/output/samples$ mosquitto_sub -h 127.0.0.1 -p 1883 -v -t "MQTT Examples"
MQTT Examples Hello World!
zhanghang@Ubuntu-14:~/MQTT/paho.mqtt.c/build/output/samples$ mosquitto_pub -h 127.0.0.1 -p 1883 -t "MQTT Examples" -m "Hello World"
zhanghang@Ubuntu-14:~/MQTT/paho.mqtt.c/build/output/samples$ ./MQTTAsync_subscribe
Successful connection
Subscribing to topic MQTT Examples
for client ExampleClientSub using QoS1
Press Q to quit
Subscribe succeeded
Message arrived
topic: MQTT Examples
message: Hello World
使用mqtt.fx应用程序测试软件成功
使用mqtt.fx订阅话题：
zhanghang@Ubuntu-14:~/MQTT/paho.mqtt.c/build/output/samples$ ./MQTTAsync_publish
Waiting for publication of Hello World!
on topic MQTT Examples for client with ClientID: ExampleClientPub
Successful connection
Message with token value 1 delivery confirmed
Successful disconnection
使用mqtt.fx推送话题：
zhanghang@Ubuntu-14:~/MQTT/paho.mqtt.c/build/output/samples$ ./MQTTAsync_subscribe
Successful connection
Subscribing to topic MQTT Examples
for client ExampleClientSub using QoS1
Press Q to quit
Subscribe succeeded
Message arrived
topic: MQTT Examples
message: hello