Possible goroutine leaks in *Client.SendEvent()

[greenhandatsjtu]

Hi there, recently I found this SDK, and it's awesome! However, when I use *Client.SendEvent in iotservice package, I encountered a weird problem, 50 minutes after calling this function, a log comes out as follows:

2021/03/22 11:41:47 ERROR put token error: amqp: session closed

And I find a issue explaning this: #38 (comment) . As the comment explains, *Client.SendEvent will result in calling *Client.putTokenContinuously:

// putTokenContinuously in v0.7.0
func (c *Client) putTokenContinuously(ctx context.Context, conn *amqp.Client) error {
	const (
		tokenUpdateInterval = time.Hour

		// we need to update tokens before they expire to prevent disconnects
		// from azure, without interrupting the message flow
		tokenUpdateSpan = 10 * time.Minute
	)

	sess, err := conn.NewSession()
	if err != nil {
		return err
	}
	defer sess.Close(context.Background())

	if err := c.putToken(ctx, sess, tokenUpdateInterval); err != nil {
		return err
	}

	go func() {
		ticker := time.NewTimer(tokenUpdateInterval - tokenUpdateSpan)
		defer ticker.Stop()

		for {
			select {
			case <-ticker.C:
				if err := c.putToken(context.Background(), sess, tokenUpdateInterval); err != nil {
					c.logger.Errorf("put token error: %s", err)
					return
				}
				ticker.Reset(tokenUpdateInterval - tokenUpdateSpan)
				c.logger.Debugf("token updated")
			case <-c.done:
				return
			}
		}
	}()
	return nil
}

This function will start a new goroutine to putToken to update session token every 50 minutes (tokenUpdateInterval - tokenUpdateSpan). However, defer sess.Close(context.Background()) means that the session will be closed when putTokenContinuously returns. As a result, putToken called in the goroutine will always fail (which will log: put token error: amqp: session closed). I notice that this problem has been fixed in recent commit (though not released yet), but here's another question:

Each time I call the *Client.SendEvent(), it will start a new session and start a goroutine to putToken every 50 minutes until the Client is closed, which means each time I send an event, a new endless goroutine is created to putToken continuously, but all I need is just sending an event, after that, I don't need to maintain this session anymore (because next time I call *Client.SendEvent(), it will start another new session for me). What's more, as I have to call *Client.SendEvent() frequently, it could lead to a large number of goroutine leak.
My solution to this problem is that the *Client.newSession() called by *Client.SendEvent() don't call putTokenContinuously, it just call putToken and return the new session.

[amenzhinsky]

Hi,

Can you try the latest master, this should fix the error

[greenhandatsjtu]

That's it. Thank you!