Class CancelPointPlacement

java.lang.Object
org.ek9lang.compiler.phase9.CancelPointPlacement
All Implemented Interfaces:
Consumer<Collection<IRConstruct>>
public final class CancelPointPlacement extends Object implements Consumer<Collection<IRConstruct>>
THE placement of CANCEL_POINT (EK9_BACKEND_IR_CONTRACTS.md Contract 24): an IR_OPTIMISATION pass over the ownership form, run after SafePointPlacement, which states which operations are callback-reachable. Only those can run on an async task - a task runs a function value's _call, and everything it calls is reached from that - so only they get cancel points, the complement of the safe points:
  • at the end of every loop body (BackEdgePoints): a task looping in EK9 code stops within one iteration;
  • at the entry of an operation that may recur - one in a cycle of the program's calls (CallbackReachableOperations.callEdges(Collection), StronglyConnectedComponents): a task recursing without a loop stops within one call. An operation that neither loops nor recurs finishes in a bounded number of steps, so it needs none. Nor does an operator the runtime calls through a vtable (CallbackReachableOperations.PREFIX_OPERATORS: _eq, _cmp, _isSet, ...): it recurs only through the value it walks - a finite structure, a cyclic one bounded by the cycle guard (Contract 13) - and the call edges join a type's overloads, so its delegation to another overload (_eq(Animal) to _eq(Cat)) would read as recursion and put the check in the hottest code there is. Its loops keep theirs.
Never in a _c_init: a class initialiser the JVM runs lazily on a task must not be left half done. Both positions hold no value in flight - the loop body's own scope has already dropped its values, and nothing is owned yet at an entry - so a cancellation unwinding from one releases only what the open scopes register. A recursion the runtime mediates (a function value handed to a runtime helper that calls it back) is not a cycle of the IR's calls; it is reached through the helper's own bound or the close's bounded join. Stateless: hold one.

  • Constructor Details

    • CancelPointPlacement

      public CancelPointPlacement()

  • Method Details