Can get into a state where flush timer is scheduled with 0 timeInterval

[julsh]

We observed some odd behavior with our freshly set up MixPanel integration where we saw in-app memory grow steadily while the app was sitting idle. Some investigation brought up the following:

// initialize mixpanel with our token
Mixpanel.initialize(token: mixpanelProjectToken, trackAutomaticEvents: true)
// manually control flush
Mixpanel.mainInstance().flushInterval = 0

We want to manually control the flushing and thus set the flushInterval to 0, according to the documentation this is how to do that. However, due to the fact that the scheduling of the flush timer inside Flush.swift is done async on the main thread, the following order of events occurs:

• MixPanel gets initialized with the default flushInterval of 60
• startFlushTimer() gets called, checks if flushInterval > 0 (which is true at this point), schedules the block that initializes the timer on the main thread
• We manually set Mixpanel.mainInstance().flushInterval = 0
• The main thread executes the block, and without an additional check for flushInterval > 0, the timer will now be scheduled with a 0 interval

I've since realized that MixPanel.initialize(...) can (and probably should be!) be called with the custom flushInterval parameter, which would avoid getting into this state. But you'll probably want to tighten up this "loophole" anyway, since it doesn't necessarily seem like an incorrect setup to initialize with default params and then do the custom setup in a next step. I'll open a PR with a fix for this.

[jaredmixpanel]

@julsh your PR is merged and released, closing this for now, feel free to re-open if the issue persists.