safe-resolve-parameter-ticks.js

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// |jit-test| skip-if: getBuildConfiguration("release_or_beta"); --enable-promise-safe-resolve

//

// resolve(thenable, true) adds exactly one extra microtask tick relative to

// resolve(thenable) — the DeferredResolveJob runs first, enqueues the

// normal PromiseResolveThenableJob, which then fulfills the outer promise.

// Baseline: resolve with a callable-then thenable, no safe-resolve.

// Tick 0 (sync): Get("then"), enqueue ThenableJob.

// Tick 1: ThenableJob runs -> thenable.then(rF, rJ) -> rF("v") -> fulfill.

// Tick 2: reaction fires.

  const thenable = {

    then(onFulfilled) { onFulfilled("baseline"); },

};

  const {promise, resolve} = Promise.withResolvers();

  resolve(thenable);  // no safe-resolve

  let ticksAtFulfill = -1;

  let tick = 0;

  promise.then(() => { ticksAtFulfill = tick; });

  // Advance a bounded number of microtask turns and see when the reaction

  // runs. Build a chain using native Promises (not the synthetic one).

  let pending = Promise.resolve();

  for (let i = 0; i < 5; i++) {

    pending = pending.then(() => { tick++; });

  drainJobQueue();

  assertEq(ticksAtFulfill >= 0, true, "reaction fired at some tick");

  // Record baseline tick count.

  var baselineTick = ticksAtFulfill;

// With safe-resolve: one extra tick.

  const thenable = {

    then(onFulfilled) { onFulfilled("safe"); },

};

  const {promise, resolve} = Promise.withResolvers();

  resolve(thenable, true);

  let ticksAtFulfill = -1;

  let tick = 0;

  promise.then(() => { ticksAtFulfill = tick; });

  let pending = Promise.resolve();

  for (let i = 0; i < 5; i++) {

    pending = pending.then(() => { tick++; });

  drainJobQueue();

  assertEq(ticksAtFulfill >= 0, true, "reaction fired at some tick");

  assertEq(ticksAtFulfill, baselineTick + 1,

           "resolve(thenable, true) takes exactly one extra microtask tick");

// Real Promise-with-Promise via safe-resolve: same +1 tick invariant.

  const inner = Promise.resolve("inner");

  const {promise: outerBase, resolve: rBase} = Promise.withResolvers();

  rBase(inner);  // baseline

  let baseTick = -1, tick = 0;

  outerBase.then(() => { baseTick = tick; });

  let chain = Promise.resolve();

  for (let i = 0; i < 6; i++) chain = chain.then(() => { tick++; });

  drainJobQueue();

  const inner2 = Promise.resolve("inner");

  const {promise: outerSafe, resolve: rSafe} = Promise.withResolvers();

  rSafe(inner2, true);

  let safeTick = -1, tick2 = 0;

  outerSafe.then(() => { safeTick = tick2; });

  let chain2 = Promise.resolve();

  for (let i = 0; i < 6; i++) chain2 = chain2.then(() => { tick2++; });

  drainJobQueue();

  assertEq(safeTick, baseTick + 1,

           "promise-with-promise via safe-resolve is +1 tick");