perf: version based tracking and link reuse

Author: brnrdog

packages/rescript-signals/src/signals/Core.res

@@ -6,6 +6,9 @@ let flag_dirty = 1
 let flag_pending = 2
 let flag_running = 4
 
+// Global tracking version counter for O(1) duplicate detection
+let trackingVersion: ref<int> = ref(0)
+
 // Observer kind tag
 type kind = [#Effect | #Computed]
 
@@ -21,6 +24,8 @@ type rec link = {
   // Links in the signal's subscriber chain
   mutable nextSub: option<link>,
   mutable prevSub: option<link>,
+  // Version stamp for O(1) duplicate detection within a compute cycle
+  mutable lastTrackedVersion: int,
 }
 
 // Signal subscriber list (head/tail of linked list)
@@ -36,6 +41,10 @@ and subs = {
   mutable lastDep: option<link>,
   mutable flags: int,
   mutable level: int,
+  // Current tracking version for this compute cycle (for link reuse)
+  mutable currentTrackingVersion: int,
+  // Whether the last recompute changed the value (for equality short-circuit)
+  mutable valueChanged: bool,
 }
 
 // Observer for effects only (computeds use subs directly)
@@ -50,6 +59,8 @@ and observer = {
   name: option<string>,
   // For computed observers: direct reference to backing subs (the combined object)
   mutable backingSubs: option<subs>,
+  // Current tracking version for this run cycle (for link reuse)
+  mutable currentTrackingVersion: int,
 }
 
 // Create empty subscriber list (for plain signals)
@@ -62,6 +73,8 @@ let makeSubs = (): subs => {
   lastDep: None,
   flags: 0,
   level: 0,
+  currentTrackingVersion: 0,
+  valueChanged: true, // Plain signals always "changed"
 }
 
 // Create subs for a computed (with compute function)
@@ -74,6 +87,8 @@ let makeComputedSubs = (compute: unit => unit): subs => {
   lastDep: None,
   flags: flag_dirty, // start dirty
   level: 0,
+  currentTrackingVersion: 0,
+  valueChanged: true, // Start as changed for initial computation
 }
 
 // Create observer
@@ -93,6 +108,7 @@ let makeObserver = (
   level: 0,
   name,
   backingSubs,
+  currentTrackingVersion: 0,
 }
 
 // Flag operations for observer (using Int.Bitwise module)
@@ -126,6 +142,7 @@ let makeLink = (subs: subs, observer: observer): link => {
   prevDep: None,
   nextSub: None,
   prevSub: None,
+  lastTrackedVersion: 0,
 }
 
 // Add link to signal's subscriber list
@@ -179,6 +196,20 @@ let unlinkFromDeps = (observer: observer, link: link): unit => {
   link.nextDep = None
 }
 
+// Remove link from subs's dependency list (for computeds - subs IS the observer)
+let unlinkFromSubsDeps = (s: subs, link: link): unit => {
+  switch link.prevDep {
+  | Some(prev) => prev.nextDep = link.nextDep
+  | None => s.firstDep = link.nextDep
+  }
+  switch link.nextDep {
+  | Some(next) => next.prevDep = link.prevDep
+  | None => s.lastDep = link.prevDep
+  }
+  link.prevDep = None
+  link.nextDep = None
+}
+
 // Clear all dependencies from observer (unlinks from all signals)
 let clearDeps = (observer: observer): unit => {
   let link = ref(observer.firstDep)