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Don't allow calling the root fiber.

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The VM used to not detect this case. It meant you could get into a
situation where another fiber's caller had completed. Then, when it
tried to resume that fiber, the VM would crash because there was nothing
to resume to.

This is part of thinking through all the cases around re-entrancy. Added
some notes for that too.
This commit is contained in:
Bob Nystrom
2018-07-21 10:02:29 -07:00
parent 5f29a72d65
commit f23c82071a
11 changed files with 240 additions and 12 deletions
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12
src/vm/wren_core.c
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@ -88,8 +88,14 @@ static bool runFiber(WrenVM* vm, ObjFiber* fiber, Value* args, bool isCall,
if (isCall)
{
// You can't call a called fiber, but you can transfer directly to it,
// which is why this check is gated on `isCall`. This way, after resuming a
// suspended fiber, it will run and then return to the fiber that called it
// and so on.
if (fiber->caller != NULL) RETURN_ERROR("Fiber has already been called.");
if (fiber->state == FIBER_ROOT) RETURN_ERROR("Cannot call root fiber.");
// Remember who ran it.
fiber->caller = vm->fiber;
}
@ -181,7 +187,7 @@ DEF_PRIMITIVE(fiber_try)
runFiber(vm, AS_FIBER(args[0]), args, true, false, "try");
// If we're switching to a valid fiber to try, remember that we're trying it.
if (IS_NULL(vm->fiber->error)) vm->fiber->callerIsTrying = true;
if (IS_NULL(vm->fiber->error)) vm->fiber->state = FIBER_TRY;
return false;
}
@ -192,7 +198,7 @@ DEF_PRIMITIVE(fiber_yield)
// Unhook this fiber from the one that called it.
current->caller = NULL;
current->callerIsTrying = false;
current->state = FIBER_OTHER;
if (vm->fiber != NULL)
{
@ -210,7 +216,7 @@ DEF_PRIMITIVE(fiber_yield1)
// Unhook this fiber from the one that called it.
current->caller = NULL;
current->callerIsTrying = false;
current->state = FIBER_OTHER;
if (vm->fiber != NULL)
{