fix: remove Go-side array ref tracking, rely on MLX-C refcounting

The Go wrapper was tracking inter-array references via desc.inputs,
creating chains that kept all intermediate arrays alive across requests.
After 3-4 requests, Metal memory grew to 170GB+ and macOS killed the
process.

Fix: remove desc.inputs/numRefs entirely. MLX-C has its own internal
reference counting — when Go GC finalizes an Array wrapper, it calls
mlx_array_free which decrements the C-side refcount. If the C-side
count reaches 0, Metal memory is freed. Go GC + MLX-C refcounting
together handle all lifecycle management correctly.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkg/mlx/array.go

@@ -16,34 +16,20 @@ import (
 	"unsafe"
 )
 
-type tensorDesc struct {
-	name    string
-	inputs  []*Array
-	numRefs int
-}
-
-// Array wraps an mlx_array handle with reference-counted memory management.
+// Array wraps an mlx_array handle.
+// Memory management relies on Go GC finalizers to call mlx_array_free,
+// which decrements MLX-C's internal reference count. MLX-C handles all
+// cross-array references internally — the Go wrapper does not track them.
 type Array struct {
 	ctx  C.mlx_array
-	desc tensorDesc
+	name string // debug label
 }
 
-// New creates a named Array tracking its input dependencies for cleanup.
-// A runtime finalizer is set so Go GC can release the C handle when
-// the Array becomes unreachable — critical because Go GC cannot see
-// Metal/C memory pressure.
+// New creates a named Array and registers a GC finalizer.
+// The inputs parameter is accepted for API compatibility but not stored —
+// MLX-C tracks inter-array references via its own refcounting.
 func New(name string, inputs ...*Array) *Array {
-	t := &Array{
-		desc: tensorDesc{
-			name:   name,
-			inputs: inputs,
-		},
-	}
-	for _, input := range inputs {
-		if input != nil {
-			input.desc.numRefs++
-		}
-	}
+	t := &Array{name: name}
 	runtime.SetFinalizer(t, finalizeArray)
 	return t
 }
@@ -63,7 +49,7 @@ type scalarTypes interface {
 // FromValue creates a scalar Array from a Go value.
 func FromValue[T scalarTypes](t T) *Array {
 	Init()
-	tt := New("") // finalizer set by New
+	tt := New("")
 	switch v := any(t).(type) {
 	case bool:
 		tt.ctx = C.mlx_array_new_bool(C.bool(v))
@@ -152,17 +138,14 @@ func Zeros(shape []int32, dtype DType) *Array {
 	return tt
 }
 
-// Set replaces this array's value with another, updating ref tracking.
+// Set replaces this array's C handle with another's.
 func (t *Array) Set(other *Array) {
-	Free(t.desc.inputs...)
-	other.desc.numRefs++
-	t.desc.inputs = []*Array{other}
 	C.mlx_array_set(&t.ctx, other.ctx)
 }
 
-// Clone creates a copy of this array sharing the same data.
+// Clone creates a new Go wrapper sharing the same C handle (increments C refcount).
 func (t *Array) Clone() *Array {
-	tt := New(t.desc.name, t.desc.inputs...)
+	tt := New(t.name)
 	C.mlx_array_set(&tt.ctx, t.ctx)
 	return tt
 }
@@ -254,33 +237,17 @@ func (t Array) Floats() []float32 {
 	return floats
 }
 
-// Free releases arrays using reference-counted cleanup.
-// Arrays with remaining references are not freed.
+// Free explicitly releases C array handles. Does not cascade — MLX-C's
+// internal refcounting handles dependent arrays automatically.
 func Free(s ...*Array) int {
 	var n int
-	free := make([]*Array, 0, 64)
-
-	fn := func(t *Array) {
+	for _, t := range s {
 		if t != nil && t.Valid() {
-			t.desc.numRefs--
-			if t.desc.numRefs <= 0 {
-				free = append(free, t.desc.inputs...)
 			n += t.NumBytes()
 			C.mlx_array_free(t.ctx)
 			t.ctx.ctx = nil
+			runtime.SetFinalizer(t, nil) // cancel finalizer
 		}
 	}
-	}
-
-	for _, t := range s {
-		fn(t)
-	}
-
-	for len(free) > 0 {
-		tail := free[len(free)-1]
-		free = free[:len(free)-1]
-		fn(tail)
-	}
-
 	return n
 }

pkg/mlx/io.go

@@ -10,6 +10,7 @@ import "C"
 
 import (
 	"iter"
+	"runtime"
 	"unsafe"
 )
 
@@ -43,7 +44,9 @@ func LoadSafetensors(path string) iter.Seq2[string, *Array] {
 			}
 
 			name := C.GoString(key)
-			if !yield(name, &Array{ctx: value, desc: tensorDesc{name: name, numRefs: 1000}}) {
+			arr := &Array{ctx: value, name: name}
+			runtime.SetFinalizer(arr, finalizeArray)
+			if !yield(name, arr) {
 				break
 			}
 		}