This solved issue #140 for me.

Maybe we should just synchronise the access to the calendar. Looking at the [apple doc](https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Multithreading/ThreadSafetySummary/ThreadSafetySummary.html), seems like NSCalendar is not thread safe. The issue is the logMessage method is executed concurrently if there are more than 1 cores available (which means most of the devices). If we sync that calendar operation
`[calendar components:calendarUnitFlags fromDate:logMessage->timestamp];` we will have logs wait on each other and become serial