Suspense #12279

acdlite · 2018-02-24T04:37:20Z

TODO:

~~Cache invalidation~~ Will work more on simple-cache-provider in a follow up
Naming things
Remove dependency on Promise.race
Dan's bug Add a failing test for nested fallbacks acdlite/react#2
Dan's other bug: It appears that suspense in <div hidden> trees is taken into account. I would expect it to be ignored. Preloading and prerendering shouldn’t affect visual indicator, and shouldn’t prevent an already suspended tree from committing when all Promises from non-hidden resolve. [Andrew: I think this is fixed]

Update (April 13)

Rebased on top of update queue changes. Now depends on #12600.

Update (April 23)

#12600 was merged.

TrySound · 2018-02-24T11:14:22Z

Awesome! But are you gonna fit this into 16.3?

gaearon · 2018-02-24T11:36:16Z

We'll see, the release has been slipping for a few weeks because some things turned out harder than we thought. Maybe 16.3 will be a bigger one than we thought.

gaearon · 2018-02-25T15:37:03Z

packages/react-reconciler/src/ReactFiberScheduler.js

+  function waitForTimeout(root, ms, suspendedTime) {
+    setTimeout(() => {
+      retryOnPromiseResolution(root, suspendedTime);
+    }, ms);


I bumped into a funny case where I accidentally clobbered the timeout queue with a bunch of setTimeouts that reschedule themselves, and the fallback never showed up for this reason. Was very tricky to debug.

gaearon · 2018-02-25T16:15:27Z

packages/react-reconciler/src/ReactFiberUnwindWork.js

+      false,
+      'An update was suspended for longer than the timeout, but no fallback ' +
+        'UI was provided.',
+    );


Can we provide a component stack trace here?

gaearon · 2018-02-25T16:20:23Z

packages/react-reconciler/src/ReactFiberScheduler.js

@@ -894,10 +964,20 @@ export default function<T, P, I, TI, HI, PI, C, CC, CX, PL>(
      } else {
        // The root did not complete.
        invariant(
-          false,
+          !nextRenderIsExpired,
          'Expired work should have completed. This error is likely caused ' +


FYI, I got here with 16.4.0-alpha.3174632

Yeah that’s the bug @ryanflorence found. Should be fixed now, haven’t pushed a new canary yet.

sebmarkbage

The more I think of it, the more I’m convinced that having the <Loading /> component wrap both the “from” screen and the “to” screen is not just a convenience but active bad pattern.

Because you start out using it by hoisting it up to a shared parent and it just works. Then you realize that you need two different loading states on the same screen depending on what the target is and you have no way of breaking this up.

It is also really impossible to have a loading state when you’re navigating to a completely different part of the app.

I wonder if we’re modeling the loading state wrong. It seems to me that it is more likely to be close to the setState that triggered the transition.

sebmarkbage · 2018-02-25T19:29:00Z

Can we split out the Timeout into a separate PR that we can land while we figure out the Loading one?

acdlite · 2018-02-27T03:34:20Z

@sebmarkbage Removed the soft expiration stuff. I'll open a separate PR for that. This one is Timeout-only.

ohyeahgotit · 2018-02-27T03:48:11Z

It already makes sense to me !!!

sebmarkbage

Let's see if we can do this without state and update queues on the component level.

I think retrying can happen on the whole root level for the timed out work.

For calling .then we can just do that eagerly and retry for each of them.

sebmarkbage · 2018-02-27T05:08:07Z

packages/react-reconciler/src/ReactFiberBeginWork.js

+      return bailoutOnAlreadyFinishedWork(current, workInProgress);
+    }
+
+    if ((workInProgress.effectTag & DidCapture) !== NoEffect) {


Ignoring legacy context you’re going to check this twice. Use a temp variable here.

sebmarkbage · 2018-02-27T05:51:45Z

packages/react-reconciler/src/ReactFiberUnwindWork.js

+    renderIsExpired,
+    remainingTimeMs,
+    renderStartTime,
+    renderExpirationTime,


These extra args are all unused.

Yeah sorry. Soft expiration vestigia.

ohyeahgotit · 2018-02-27T19:30:38Z

Please tell me what suspense and what will all make sense ??

acdlite · 2018-02-28T00:43:13Z

@ohyeahgotit If you're curious, you can watch Dan's talk this Thursday at JSConf Iceland.

nihgwu · 2018-02-28T03:02:37Z

packages/shared/ReactTypeOfWork.js

@@ -37,3 +37,4 @@ export const Fragment = 10;
 export const Mode = 11;
 export const ContextConsumer = 12;
 export const ContextProvider = 13;
+export const TimeoutComponent = 15;


should be 14 here for consistence and also added to TypeOfWork above?

It's probably because @acdlite redacted LoadingComponent to keep us in suspense until @gaearon's talk 🤫

mobilespace · 2018-03-01T11:01:00Z

well played @acdlite 👏

Nimelrian · 2018-03-01T11:02:22Z

Reactiflux's reaction to Dan's talk (IO Demo).

bpartridge · 2018-03-01T17:43:53Z

For anyone just following this on Github, you can see a roundup of links to the talk and implementation comments here: https://news.ycombinator.com/item?id=16492973

And the money image:

goldenice · 2018-03-04T11:26:51Z

I am a very big fan of this API, I think the whole idea behind it is superb, kudo's to everyone involved! 👍

One thing I was wondering about though: it seems that the deferred setState is the only way to use the suspense feature. Am I correct in assuming that? Because that would mean that a update triggered per prop would not work, which would be bad news for Redux-heavy applications. Effectively that would limit the scope of to within presentational components: everything 'above' a connected component in the tree couldn't use this.

gaearon · 2018-03-04T13:39:45Z

it seems that the deferred setState is the only way to use the suspense feature. Am I correct in assuming that?

Not quite. You can use it with regular setState but it will have a very small expiration time. So it’ll be like if you set the Placeholder timeout to a low value, and will switch to loading state very quickly.

Because that would mean that a update triggered per prop would not work, which would be bad news for Redux-heavy applications

We don’t even have a real API for doing deferred updates yet so this is a premature conclusion.

The real problem with Redux is it only has a concept of one current state. But with suspense you have two. React can handle this but Redux currently doesn’t. This is a much bigger problem that needs to be solved.

We have some ideas on how we can make suspense work with Redux but it’ll take some time and likely some API changes. The issue you pointed out is just a small part of the problem.

Nimelrian · 2018-03-04T13:43:40Z

Quick question: if my render calls 3 fetchers, each of which doesn't have the requested value cached, how long would it take at least to render my component when each fetcher takes 500ms to get the data? From what I can tell they are executed in sequence, not parallel, so it would take at least 1500ms (just for the fetching).

gaearon · 2018-03-04T15:33:40Z

Yes, calling multiple fetchers from one component when they don’t strictly depend on one another can be considered a bad practice. You can solve this either by putting them in sibling components (they are parallel) or by using a combinator similar to Promise.all. We might provide one in the final API.

Edit: Nope, I’m wrong #12279 (comment)

sebmarkbage · 2018-03-04T19:36:18Z

@gaearon No that is fine practice. Using a Promise.all might in fact be bad practice since it doesn’t let individual values share the cache.

The solution is to use preload.

preload(a);
preload(b);
return read(a) + read(b);

Where preload should ideally be hoisted even further up if possible.

sebmarkbage · 2018-03-05T01:08:09Z

Another problem with Promise.all is that people tend to think that it’s good to “batch” work. That often leads to a situation where everything is hoisted to a top Promise.all and you can’t do any work until all dependencies are satisfied. That leads to worse parallelization of CPU work.

The preload technique avoids that problem but does require adding code to two places. However, tooling should be able to provide good hints.

acdlite · 2018-05-10T00:13:48Z

Things to address in follow-up PRs:

Immediately...

Switching back from a placeholder to the normal view should also be suspendy, not immediately time out. I had this working properly at one point but must not have tested it properly.
Round the user provided timeouts to the nearest "just noticeable" threshold, taking into account how much time has already elapsed.
Speculatively render the placeholder view immediately upon suspending so it is ready to commit upon timeout. We don't need proper resuming because we can complete the entire root. This should be unified with how root.createBatch works.

After that...

Consider renaming Timeout to Placeholder.
Consider adding hidden support to fragments so we can hide a timed out tree without losing state and without adding superfluous host nodes. Also consider adding this feature to the built-in placeholder primitive.
Improvements to simple-cache-provider
- Per-key invalidation
- Subscriptions
- Garbage collection

At this point I think we'll have an MVP. Then...

Future

Implement "soft" expiration. Probably something like ReactDOM.loadingUpdates(batch, onSuspend, onResume)

sebmarkbage · 2018-05-10T01:28:09Z

packages/react-reconciler/src/ReactFiberExpirationTime.js

-    bucketSizeMs / UNIT_SIZE,
+  return (
+    MAGIC_NUMBER_OFFSET +
+    round(


Why this change? What happens if you move this to a follow up?

When I made the change to infer the start time from the expiration time, all the numbers in the tests were off by 250ms (the bucket size) because we were rounding up. Since in practice it doesn’t really matter if we round up or down when placing updates into buckets, I adjusted it here rather than change all the tests and introduce more noise to the diff.

sebmarkbage · 2018-05-10T03:08:47Z

packages/react-reconciler/src/ReactFiberPendingPriority.js

+
+import {enableSuspense} from 'shared/ReactFeatureFlags';
+
+// TODO: Offscreen updates


What is this? It doesn't seem to be on your follow up list.

sebmarkbage · 2018-05-10T06:35:01Z

packages/react-reconciler/src/ReactFiberRoot.js

@@ -28,6 +28,13 @@ export type FiberRoot = {
  pendingChildren: any,
  // The currently active root fiber. This is the mutable root of the tree.
  current: Fiber,
+


Comments plz. What are these for?

Ok I’ll add comments in the morning

sebmarkbage · 2018-05-10T06:54:16Z

packages/react-reconciler/src/ReactFiberPendingPriority.js

+  }
+}
+
+export function flushPendingPriorityLevel(


Flush means something else in the scheduler context. This is more like update something based on something else flushing. This is not the flush.

Huh this is called after a commit, so “flush” seemed appropriate. Suggestions?

sebmarkbage · 2018-05-10T07:17:03Z

packages/react-reconciler/src/ReactFiberUnwindWork.js

+          if (current !== null && current.memoizedState === true) {
+            // A parent Timeout already committed in a placeholder state. We
+            // need to handle this promise immediately. In other words, we
+            // should never suspend inside a tree that already expired.


So this is the thing you're going to fix in the follow up?

Yeah, this is the first bullet

sebmarkbage · 2018-05-10T07:17:42Z

packages/react-reconciler/src/ReactFiberUnwindWork.js

+        thenable.then(onResolveOrReject, onResolveOrReject);
+        return;
+      } else {
+        // No time remaining. Need to fallback to palceholder.


palceholder -> placeholder

sebmarkbage · 2018-05-10T07:24:51Z

packages/react-reconciler/src/ReactFiberRoot.js

@@ -28,6 +28,13 @@ export type FiberRoot = {
  pendingChildren: any,
  // The currently active root fiber. This is the mutable root of the tree.
  current: Fiber,
+
+  earliestPendingTime: ExpirationTime,
+  latestPendingTime: ExpirationTime,


I don't get why we need to keep track of these two pending times.

Why isn't earliestPendingTime just root.current.expirationTime and latestPendingTime just earliestSuspendedTime - 1? Effectively.

The pending times are levels we haven’t tried yet. If we try them and they suspend, they are cleared. In other words, need to distinguish between “incomplete” and “incomplete and suspended.”

Adds Timeout component. If a promise is thrown from inside a Timeout component, React will suspend the in-progress render from committing. When the promise resolves, React will retry. If the render is suspended for longer than the maximum threshold, the Timeout switches to a placeholder state. The timeout threshold is defined as the minimum of: - The expiration time of the current render - The `ms` prop given to each Timeout component in the ancestor path of the thrown promise.

Co-authored-by: Andrew Clark <acdlite@fb.com>

React should resume rendering regardless of whether it resolves or rejects.

Async is not required for Suspense, but strict mode is.

Some of this was added with "soft expiration" in mind, but now with our revised model for how soft expiration will work, this isn't necessary. It would be nice to remove more of this, but I think the list itself is inherent because we need a way to track the start times, for <Timeout ms={ms} />.

It already worked this way in practice.

Instead of waiting for commit phase.

We can replicate almost all the functionality by tracking just five separate levels: the highest/lowest priority pending levels, the highest/lowest priority suspended levels, and the lowest pinged level. We lose a bit of granularity, in that if there are multiple levels of pending updates, only the first and last ones are known. But in practice this likely isn't a big deal. These heuristics are almost entirely isolated to a single module and can be adjusted later, without API changes, if necessary. Non-IO-bound work is not affected at all.

Idk why I thought this was neccessary

This means you have to account for the start time approximation heuristic when writing Suspense tests, but that's going to be true regardless. When updating the tests, I also made a fix related to offscreen priority. We should never timeout inside a hidden tree.

gaearon · 2018-05-23T11:41:46Z

I don't think <div hidden> is an actual API for this feature. It's currently disabled and we might have a proper API as you suggested later. That said hidden is an actual HTML attribute that denotes something is hidden.

acdlite requested a review from sebmarkbage February 24, 2018 04:37

facebook-github-bot added the CLA Signed label Feb 24, 2018

acdlite force-pushed the suspense branch from 546e617 to e50e950 Compare February 25, 2018 08:07

gaearon reviewed Feb 25, 2018

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sebmarkbage reviewed Feb 25, 2018

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acdlite force-pushed the suspense branch 2 times, most recently from f215727 to 7166ce6 Compare February 27, 2018 03:32

sebmarkbage requested changes Feb 27, 2018

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nihgwu reviewed Feb 28, 2018

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acdlite changed the title ~~[WIP] This will all make sense, soon~~ [WIP] Suspense Mar 1, 2018

thysultan mentioned this pull request Mar 2, 2018

[intent to implement] Timeout, Suspense dyo/dyo#51

Closed

lmatteis mentioned this pull request Mar 5, 2018

React suspense reduxjs/redux#2867

Closed

acdlite force-pushed the suspense branch from d19fd0a to 0717641 Compare May 9, 2018 23:58

sebmarkbage reviewed May 10, 2018

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acdlite and others added 18 commits May 10, 2018 15:55

Add a test for nested fallbacks

46902d6

Co-authored-by: Andrew Clark <acdlite@fb.com>

Resume on promise rejection

680f88d

React should resume rendering regardless of whether it resolves or rejects.

Wrap Suspense code in feature flag

db763cc

Children of a Timeout must be strict mode compatible

64cb6a4

Async is not required for Suspense, but strict mode is.

Only use the Timeout update queue to store promises, not for state

fd224f1

It already worked this way in practice.

Wrap more Suspense-only paths in the feature flag

c3a36af

Attach promise listener immediately on suspend

86ccbea

Instead of waiting for commit phase.

Infer approximate start time using expiration time

c562440

ReactFiberPendingWork -> ReactFiberPendingPriority

4453b5f

Renaming method names from "pending work" to "pending priority"

e86acde

Get rid of SuspenseThenable module

89aa15c

Idk why I thought this was neccessary

Nits based on Sebastian's feedback

ed8aaf0

More naming nits + comments

abc5c05

Add test for hiding a suspended tree to unblock

73c1643

acdlite force-pushed the suspense branch from 86a49da to c9bb461 Compare May 10, 2018 23:05

palceholder -> placeholder

b624acb

acdlite force-pushed the suspense branch from e16c7db to b624acb Compare May 10, 2018 23:14

sebmarkbage approved these changes May 11, 2018

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acdlite merged commit 6565795 into facebook:master May 11, 2018

gaearon mentioned this pull request May 14, 2018

Support for asynchronous values (like Promises and Observables) #6481

Closed

priley86 mentioned this pull request May 24, 2018

feat(simple redux): implement simple redux helpers to register and remove reducers patternfly/patternfly-react#358

Closed

swyxio mentioned this pull request Jan 18, 2022

React Suspense Q&A swyxio/swyxdotio#268

Closed


		import {enableSuspense} from 'shared/ReactFeatureFlags';

		// TODO: Offscreen updates

Suspense #12279

Suspense #12279

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acdlite commented Feb 24, 2018 • edited Loading

Update (April 13)

Update (April 23)

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sebmarkbage commented Mar 5, 2018

acdlite commented May 10, 2018 • edited Loading

Immediately...

After that...

Future

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gaearon commented May 23, 2018

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