Consider adding a way to register explicit on-terminate callbacks from within a coroutine.

[jmalloc]

Because there is no way to force-close a generator, finally blocks can not (necessarily) be relied upon for deterministic execution.

$coroutine = function () {
   yield Recoil::onTerminate(function () { });
};

The callback would be called if the coroutine ticks after terminateOnNextTick() has been called, rather than attaching a handler directly to the strand's terminate event.

Something like this may allow some of the kernel API to be implemented more concisely as coroutines.

[jmalloc]

Could also be implemented as:

$coroutine = function () {
  yield Recoil::finally_(function ($exception) {});
}

Where $exception is set to the exception that is causing the stack unwind, or StrandTerminateException on termination. The exception would be null if the coroutine returned a value normally.