Well you went unsafe by using cast[ptr History] and that's what you get when
you modify one gc backed object from another thread, by adding foreign thread
gc objects to it. This is happening because every thread has its own "heap" and
his own GC. And every GC once finds a ref requires it to be either nil or
originated from its own heap. Example:
type Foo = object
next: ref Foo
proc backgroundThread(f: ptr Foo) =
f.next.new()
proc mainThread() =
var f: ref Foo
f.new()
spawn backgroundThread(cast[ptr Foo](f))
Run
I haven't tested the above code if it compiles, but hopefully the idea is clear.
