How to implement and expose a timer with expvar for performance monitoring in Go?

To implement and expose a timer with expvar for performance monitoring in Go, you can follow these steps:

Step 1: Create a new Go file, for example "timer.go", and import the required packages:

package main

import (
	"expvar"
	"sync"
	"time"
)

Step 2: Define a struct to hold the timer information and methods:

type Timer struct {
	mu      sync.Mutex
	elapsed time.Duration
}

func (t *Timer) Start() {
	t.mu.Lock()
	t.elapsed = 0
	t.mu.Unlock()
}

func (t *Timer) Stop() {
	t.mu.Lock()
	t.elapsed += time.Since(time.Now())
	t.mu.Unlock()
}

In the above code, we use the sync.Mutex to safely update the timer information and the time.Since() function to calculate the elapsed time.

Step 3: Define expvar variables and register them:

var timer Timer

func init() {
	expvar.Publish("timer", expvar.Func(func() interface{} {
		return timer.elapsed
	}))
}

In the above code, we create a variable timer of Timer type and publish it as an expvar variable named "timer". We use the expvar.Func function to define a function that returns the value of timer.elapsed.

Step 4: Start and stop the timer as needed:

func main() {
	timer.Start()

	time.Sleep(2 * time.Second) // Some operation

	timer.Stop()
}

In the above code, we call Start() to reset the timer and Stop() to calculate the elapsed time.

Step 5: Run the application:

go run timer.go

Step 6: Access the exposed timer information:

The timer information can be accessed by visiting the /debug/vars endpoint of your Go application. For example, if you are running the application locally, you can access it at http://localhost:port/debug/vars. Look for the "timer" variable to find the elapsed time in nanoseconds.

That's it! You have successfully implemented and exposed a timer with expvar for performance monitoring in Go.