feat(swingset): allow buildRootObject to return a Promise #5249
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New (or upgraded) vats are defined by a user-provided `buildRootObject` function. This function has two responsibilities: * provide a root object * use `defineDurableKind` to bind behavior to any pre-existing durable kinds Previously, `buildRootObject` was given exactly one "turn" to fulfill these responsibilities: it was required to return the root object synchronously. If it returned a Promise, that was rejected as an error. This requirement is at odds with the needs for updated ZCF vats to evaluate their contract code and interact with it (giving the contract a chance to bind their own Kind behavior). The `importBundle` function we use to load contracts is async. However, it is still "prompt": it needs no IO, nor any messages leaving the vat. So it will still complete within the *crank*, just not synchronously within the turn. So this commit changes liveslots to allow `buildRootObject` to return a Promise for the root object. The requirement, however, is that this Promise must resolve by the end of the initial crank (before `waitUntilQuiescent` / `setImmediate` determines that the promise queue is empty). If the Promise is not fulfilled by then, the vat creation/update is considered broken. closes #5246
mhofman
approved these changes
Apr 29, 2022
| return gcTools.waitUntilQuiescent().then(() => { | ||
| afterDispatchActions(); | ||
| return p; | ||
| // eslint-disable-next-line prefer-promise-reject-errors | ||
| return complete ? p : Promise.reject('buildRootObject unresolved'); |
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The not complete rejection is technically not startVat/buildRootObject specific, right? In practice it doesn't happen for other deliveries, but I'm a little concerned about using a specific call out here as it may be confusing to readers.
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Correct.. the only dispatch that pays attention to a userspace-provided Promise is startVat, so the only place that can cause !complete is buildRootObject, so the error message is specialized. I'll add a comment to that effect.
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oops, I deleted the branch when I meant to be updating it |
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GitHub wouldn't let me re-open this PR, so I opened a new one: #5250 |
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New (or upgraded) vats are defined by a user-provided
buildRootObjectfunction. This function has two responsibilities:defineDurableKindto bind behavior to any pre-existing durablekinds
Previously,
buildRootObjectwas given exactly one "turn" to fulfillthese responsibilities: it was required to return the root object
synchronously. If it returned a Promise, that was rejected as an
error.
This requirement is at odds with the needs for updated ZCF vats to
evaluate their contract code and interact with it (giving the contract
a chance to bind their own Kind behavior). The
importBundlefunctionwe use to load contracts is async. However, it is still "prompt": it
needs no IO, nor any messages leaving the vat. So it will still
complete within the crank, just not synchronously within the turn.
So this commit changes liveslots to allow
buildRootObjectto returna Promise for the root object. The requirement, however, is that this
Promise must resolve by the end of the initial crank (before
waitUntilQuiescent/setImmediatedetermines that the promisequeue is empty). If the Promise is not fulfilled by then, the vat
creation/update is considered broken.
closes #5246