From 344d458fd2aaff4af791e89fce19f22101790741 Mon Sep 17 00:00:00 2001
From: David Maskasky <dmaskasky@gmail.com>
Date: Fri, 5 Dec 2025 00:14:34 -0800
Subject: [PATCH 1/3] only mounted dependents can be added to mounted.t

---
 src/vanilla/internals.ts | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/vanilla/internals.ts b/src/vanilla/internals.ts
index 44a3de4590..3cf1053ced 100644
--- a/src/vanilla/internals.ts
+++ b/src/vanilla/internals.ts
@@ -303,9 +303,7 @@ function getMountedOrPendingDependents(
 ): Set<AnyAtom> {
   const dependents = new Set<AnyAtom>()
   for (const a of mountedMap.get(atom)?.t || []) {
-    if (mountedMap.has(a)) {
-      dependents.add(a)
-    }
+    dependents.add(a)
   }
   for (const atomWithPendingPromise of atomState.p) {
     dependents.add(atomWithPendingPromise)
@@ -598,7 +596,9 @@ const readAtomState: ReadAtomState = (store, atom) => {
       if (isPendingPromise(atomState.v)) {
         addPendingPromiseToDependency(atom, atomState.v, aState)
       }
-      mountedMap.get(a)?.t.add(atom)
+      if (mountedMap.has(atom)) {
+        mountedMap.get(a)?.t.add(atom)
+      }
       if (!isSync) {
         mountDependenciesIfAsync()
       }

From fbb23df0c72f08af043805aa0642d1877d385dec Mon Sep 17 00:00:00 2001
From: David Maskasky <dmaskasky@gmail.com>
Date: Fri, 5 Dec 2025 00:34:05 -0800
Subject: [PATCH 2/3] improve perf

---
 src/vanilla/internals.ts | 34 ++++++++++++++++++++--------------
 1 file changed, 20 insertions(+), 14 deletions(-)

diff --git a/src/vanilla/internals.ts b/src/vanilla/internals.ts
index 3cf1053ced..e693f96a84 100644
--- a/src/vanilla/internals.ts
+++ b/src/vanilla/internals.ts
@@ -553,14 +553,14 @@ const readAtomState: ReadAtomState = (store, atom) => {
     }
     // Otherwise, check if the dependencies have changed.
     // If all dependencies haven't changed, we can use the cache.
-    if (
-      Array.from(atomState.d).every(
-        ([a, n]) =>
-          // Recursively, read the atom state of the dependency, and
-          // check if the atom epoch number is unchanged
-          readAtomState(store, a).n === n,
-      )
-    ) {
+    let hasChangedDeps = false
+    for (const [a, n] of atomState.d) {
+      if (readAtomState(store, a).n !== n) {
+        hasChangedDeps = true
+        break
+      }
+    }
+    if (!hasChangedDeps) {
       return atomState
     }
   }
@@ -771,7 +771,7 @@ const mountDependencies: MountDependencies = (store, atom) => {
         }
       }
     }
-    for (const a of mounted.d || []) {
+    for (const a of mounted.d) {
       if (!atomState.d.has(a)) {
         mounted.d.delete(a)
         const aMounted = unmountAtom(store, a)
@@ -854,11 +854,17 @@ const unmountAtom: UnmountAtom = (store, atom) => {
   const unmountAtom = buildingBlocks[19]
   const atomState = ensureAtomState(store, atom)
   let mounted = mountedMap.get(atom)
-  if (
-    mounted &&
-    !mounted.l.size &&
-    !Array.from(mounted.t).some((a) => mountedMap.get(a)?.d.has(atom))
-  ) {
+  if (!mounted || mounted.l.size) {
+    return mounted
+  }
+  let isDependent = false
+  for (const a of mounted.t) {
+    if (mountedMap.get(a)?.d.has(atom)) {
+      isDependent = true
+      break
+    }
+  }
+  if (isDependent) {
     // unmount self
     if (mounted.u) {
       unmountCallbacks.add(mounted.u)

From e89dd4053cf5639ae3ae6f1f11c9e3e04b8c380f Mon Sep 17 00:00:00 2001
From: David Maskasky <dmaskasky@gmail.com>
Date: Fri, 5 Dec 2025 10:27:17 -0800
Subject: [PATCH 3/3] fix failing test by inverting isDependent condition

---
 src/vanilla/internals.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/vanilla/internals.ts b/src/vanilla/internals.ts
index e693f96a84..1926a51338 100644
--- a/src/vanilla/internals.ts
+++ b/src/vanilla/internals.ts
@@ -864,7 +864,7 @@ const unmountAtom: UnmountAtom = (store, atom) => {
       break
     }
   }
-  if (isDependent) {
+  if (!isDependent) {
     // unmount self
     if (mounted.u) {
       unmountCallbacks.add(mounted.u)