I am currently testing rabbitmq with golang (github.com/streadway/amqp), and I have three programs, two of them sending messages to the queue with different priorities and one reading from the queue.
And the problem I am having is that after sending a few messages with the two programs I then proceed to launch the program that will read from the queue and when it starts to read from the queue it output the result like a FIFO.
I expected to output the high priority first followed by the lower priority message.
Did I misunderstand how rabbitmq works or am I doing something wrong?
Sending to queues package main
import (
"log"
"github.com/streadway/amqp"
)
func failOnError(err error, msg string) {
if err != nil {
log.Fatalf("%s: %s", msg, err)
}
}
func main() {
args := make(amqp.Table)
args["x-max-priority"] = int64(9)
conn, err := amqp.Dial("amqp://guest:guest@localhost:5672/")
failOnError(err, "Failed to connect to RabbitMQ")
defer conn.Close()
ch, err := conn.Channel()
failOnError(err, "Failed to open a channel")
defer ch.Close()
q, err := ch.QueueDeclare(
"test", // name
false, // durable
false, // delete when unused
false, // exclusive
false, // no-wait
args, // arguments
)
failOnError(err, "Failed to declare a queue")
body := "low"
err = ch.Publish(
"", // exchange
q.Name, // routing key
false, // mandatory
false, // immediate
amqp.Publishing{
Headers: amqp.Table{},
ContentType: "text/plain",
ContentEncoding: "",
Body: []byte(body),
DeliveryMode: amqp.Transient, // 1=non-persistent, 2=persistent
Priority: 0,
})
log.Printf(" [x] Sent %s", body)
failOnError(err, "Failed to publish a message")
body = "low"
err = ch.Publish(
"", // exchange
q.Name, // routing key
false, // mandatory
false, // immediate
amqp.Publishing{
Headers: amqp.Table{},
ContentType: "text/plain",
ContentEncoding: "",
Body: []byte(body),
DeliveryMode: amqp.Transient, // 1=non-persistent, 2=persistent
Priority: 0,
})
log.Printf(" [x] Sent %s", body)
failOnError(err, "Failed to publish a message")
body = "low"
err = ch.Publish(
"", // exchange
q.Name, // routing key
false, // mandatory
false, // immediate
amqp.Publishing{
Headers: amqp.Table{},
ContentType: "text/plain",
ContentEncoding: "",
Body: []byte(body),
DeliveryMode: amqp.Transient, // 1=non-persistent, 2=persistent
Priority: 0,
})
log.Printf(" [x] Sent %s", body)
failOnError(err, "Failed to publish a message")
body = "high"
err = ch.Publish(
"", // exchange
q.Name, // routing key
false, // mandatory
false, // immediate
amqp.Publishing{
Headers: amqp.Table{},
ContentType: "text/plain",
ContentEncoding: "",
Body: []byte(body),
DeliveryMode: amqp.Transient, // 1=non-persistent, 2=persistent
Priority: 9,
})
log.Printf(" [x] Sent %s", body)
failOnError(err, "Failed to publish a message")
body = "low"
err = ch.Publish(
"", // exchange
q.Name, // routing key
false, // mandatory
false, // immediate
amqp.Publishing{
Headers: amqp.Table{},
ContentType: "text/plain",
ContentEncoding: "",
Body: []byte(body),
DeliveryMode: amqp.Transient, // 1=non-persistent, 2=persistent
Priority: 0,
})
log.Printf(" [x] Sent %s", body)
failOnError(err, "Failed to publish a message")
body = "low"
err = ch.Publish(
"", // exchange
q.Name, // routing key
false, // mandatory
false, // immediate
amqp.Publishing{
Headers: amqp.Table{},
ContentType: "text/plain",
ContentEncoding: "",
Body: []byte(body),
DeliveryMode: amqp.Transient, // 1=non-persistent, 2=persistent
Priority: 0,
})
log.Printf(" [x] Sent %s", body)
failOnError(err, "Failed to publish a message")
body = "low"
err = ch.Publish(
"", // exchange
q.Name, // routing key
false, // mandatory
false, // immediate
amqp.Publishing{
Headers: amqp.Table{},
ContentType: "text/plain",
ContentEncoding: "",
Body: []byte(body),
DeliveryMode: amqp.Transient, // 1=non-persistent, 2=persistent
Priority: 0,
})
log.Printf(" [x] Sent %s", body)
failOnError(err, "Failed to publish a message")
}
Reading queue:
package main
import (
"log"
"github.com/streadway/amqp"
)
func failOnError(err error, msg string) {
if err != nil {
log.Fatalf("%s: %s", msg, err)
}
}
func main() {
args := make(amqp.Table)
args["x-max-priority"] = int64(9)
conn, err := amqp.Dial("amqp://guest:guest@localhost:5672/")
failOnError(err, "Failed to connect to RabbitMQ")
ch, err := conn.Channel()
failOnError(err, "Failed to open a channel")
q, err := ch.QueueDeclare(
"test", // name
false, // durable
false, // delete when unused
false, // exclusive
false, // no-wait
args, // arguments
)
failOnError(err, "Failed to declare a queue")
msgs, err := ch.Consume(
q.Name, // queue
"", // consumer
true, // auto-ack
false, // exclusive
false, // no-local
false, // no-wait
args, // args
)
failOnError(err, "Failed to register a consumer")
defer ch.Close()
defer conn.Close()
forever := make(chan bool)
go func() {
for d := range msgs {
log.Printf("Received a message: %s", d.Body)
}
}()
log.Printf(" [*] Waiting for messages. To exit press CTRL+C")
<-forever
}
First I launch the code sending the messages to the queue the following values:
- low
- low
- low
- high
- low
- low
- low
With the low messages having a priority of 0 and the high a priority of 9.
Then I launch the program that will receive the queue.
Expected output:
- high
- low
- low
- low
- low
- low
- low
Actual output:
- low
- low
- low
- high
- low
- low
- low
Thank you
