fix(preloader): highly likely = likely

Author: wmertens

packages/qwik/src/core/preloader/bundle-graph.ts

@@ -31,7 +31,11 @@ export const parseBundleGraph = (serialized: (string | number)[]) => {
       if (idx < 0) {
         probability = -idx / 10;
       } else {
-        deps.push({ $name$: serialized[idx] as string, $probability$: probability, $factor$: 1 });
+        deps.push({
+          $name$: serialized[idx] as string,
+          $importProbability$: probability,
+          $factor$: 1,
+        });
       }
       i++;
     }

packages/qwik/src/core/preloader/preloader.unit.ts

@@ -21,5 +21,5 @@ test('preloader script', () => {
    * dereference objects etc, but that actually results in worse compression
    */
   const compressed = compress(Buffer.from(preLoader), { mode: 1, quality: 11 });
-  expect([compressed.length, preLoader.length]).toEqual([1785, 5285]);
+  expect([compressed.length, preLoader.length]).toEqual([1816, 5423]);
 });

packages/qwik/src/core/preloader/queue.ts

@@ -82,8 +82,8 @@ export const trigger = () => {
         Math.max(1, config.$maxIdlePreloads$ * probability)
       : // While the graph is not available, we limit to 2 preloads
         2;
-    // When we're 100% sure, everything needs to be queued
-    if (probability === 1 || preloadCount < allowedPreloads) {
+    // When we're 99% sure, everything needs to be queued
+    if (probability >= 0.99 || preloadCount < allowedPreloads) {
       queue.shift();
       preloadOne(bundle);
     } else {
@@ -142,17 +142,27 @@ const preloadOne = (bundle: BundleImport) => {
   doc.head.appendChild(link);
 };
 
+/**
+ * Adjust the probability of a bundle based on the probability of its dependent bundles, and queue
+ * it if it's likely enough to be preloaded.
+ *
+ * Note that if the probability is 100%, we treat the dynamic imports as 99% sure, and both will be
+ * preloaded without limit.
+ *
+ * We also limit "organic" probability to 98% so they don't get unlimited preloads.
+ */
 export const adjustProbabilities = (
   bundle: BundleImport,
-  adjustFactor: number,
+  newInverseProbability: number,
   seen?: Set<BundleImport>
 ) => {
   if (seen?.has(bundle)) {
     return;
   }
 
   const previousInverseProbability = bundle.$inverseProbability$;
-  bundle.$inverseProbability$ *= adjustFactor;
+  bundle.$inverseProbability$ = newInverseProbability;
+  // Don't propagate tiny changes
   if (previousInverseProbability - bundle.$inverseProbability$ < 0.01) {
     return;
   }
@@ -178,6 +188,10 @@ export const adjustProbabilities = (
     const probability = 1 - bundle.$inverseProbability$;
     for (const dep of bundle.$deps$) {
       const depBundle = getBundle(dep.$name$)!;
+      if (depBundle.$inverseProbability$ === 0) {
+        // it's already at max probability
+        continue;
+      }
       const prevAdjust = dep.$factor$;
       /**
        * The chance that a dep won't be loaded is 1-(the chance that the dep will be loaded)*(the
@@ -189,14 +203,20 @@ export const adjustProbabilities = (
        * But when we're very likely to load the current bundle, make the dynamic imports very likely
        * too.
        */
-      const newInverseProbability =
-        dep.$probability$ !== 1 && adjustFactor < 0.1 ? 0.01 : 1 - dep.$probability$ * probability;
+      let newInverseProbability: number;
+      if (probability >= 0.99) {
+        // we're loaded at max probability, so elevate dynamic imports to 99% sure
+        newInverseProbability = Math.min(0.01, 1 - dep.$importProbability$);
+      } else {
+        const newInverseImportProbability = 1 - dep.$importProbability$ * probability;
+        const factor = newInverseImportProbability / prevAdjust;
+        // limit organic probability to 98%
+        newInverseProbability = Math.max(0.02, depBundle.$inverseProbability$ * factor);
+        dep.$factor$ = factor;
+      }
 
       /** We need to undo the previous adjustment */
-      const factor = newInverseProbability / prevAdjust;
-      dep.$factor$ = factor;
-
-      adjustProbabilities(depBundle, factor, seen);
+      adjustProbabilities(depBundle, newInverseProbability, seen);
     }
   }
 };

packages/qwik/src/core/preloader/types.ts

@@ -24,7 +24,7 @@ export type ImportProbability = {
   /** Bundle name */
   $name$: string;
   /** Probability */
-  $probability$: number;
+  $importProbability$: number;
   /** Probability adjust factor */
   $factor$: number;
 };