Types

NestedPoll = object of RootEffect
  

Nested poll calls are those where poll (or waitFor) is called from within the call stack of another poll call - this can happen if a call scheduled with callSoon gets called as part of event loop processing, as happens with async continuations.

Such nested calls are undefined behavior since they re-enter the event loop and cause events to be handled out of order with respect to how they are polled from the operating system.

When deeply nested, it can also quickly exhaust available stack space and cause other forms of undefined behavior.

The nested poll effect helps prevent obvious cases of poll being called inside async functions, though not all such calls can be detected at compile time currently.

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