diff --git a/runtime/build.go b/runtime/build.go
index 8afce1cc69..0764eadce5 100644
--- a/runtime/build.go
+++ b/runtime/build.go
@@ -61,6 +61,7 @@ var altPkgs = map[string]altPkgSpec{
 	"reflect":                 {mode: altPkgReplace},
 	"runtime":                 {mode: altPkgReplace},
 	"sync/atomic":             {mode: altPkgReplace},
+	"sync":                    {mode: altPkgReplace},
 	"syscall/js":              {mode: altPkgReplace},
 	"syscall":                 {mode: altPkgReplace},
 	"unique":                  {mode: altPkgReplace},
diff --git a/runtime/internal/lib/runtime/sync_runtime_llgo.go b/runtime/internal/lib/runtime/sync_runtime_llgo.go
index cee3441a8d..8cddac6795 100644
--- a/runtime/internal/lib/runtime/sync_runtime_llgo.go
+++ b/runtime/internal/lib/runtime/sync_runtime_llgo.go
@@ -2,7 +2,10 @@
 
 package runtime
 
-import _ "unsafe"
+import (
+	_ "sync/atomic"
+	_ "unsafe"
+)
 
 var poolCleanup func()
 
diff --git a/runtime/internal/lib/runtime/unique_runtime_llgo.go b/runtime/internal/lib/runtime/unique_runtime_llgo.go
index 887db777cf..26edac0047 100644
--- a/runtime/internal/lib/runtime/unique_runtime_llgo.go
+++ b/runtime/internal/lib/runtime/unique_runtime_llgo.go
@@ -3,8 +3,9 @@
 package runtime
 
 import (
-	"sync"
 	_ "unsafe"
+
+	"github.com/goplus/llgo/runtime/internal/clite/pthread/sync"
 )
 
 var (
@@ -13,15 +14,17 @@ var (
 )
 
 //go:linkname unique_runtime_registerUniqueMapCleanup unique.runtime_registerUniqueMapCleanup
-func unique_runtime_registerUniqueMapCleanup(cleanup func()) {
+func unique_runtime_registerUniqueMapCleanup(f func()) {
 	uniqueMapCleanupOnce.Do(func() {
 		uniqueMapCleanup = make(chan struct{}, 1)
-		go func() {
-			for range uniqueMapCleanup {
-				cleanup()
-			}
-		}()
 	})
+	// Start the goroutine in the runtime so it's counted as a system goroutine.
+	go func(cleanup func()) {
+		for {
+			<-uniqueMapCleanup
+			cleanup()
+		}
+	}(f)
 }
 
 func unique_runtime_notifyMapCleanup() {
diff --git a/runtime/internal/lib/sync/pool.go b/runtime/internal/lib/sync/pool.go
new file mode 100644
index 0000000000..08227e713d
--- /dev/null
+++ b/runtime/internal/lib/sync/pool.go
@@ -0,0 +1,184 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sync
+
+import (
+	"sync"
+	"sync/atomic"
+	"unsafe"
+
+	"github.com/goplus/llgo/runtime/internal/clite/tls"
+)
+
+// A Pool is a set of temporary objects that may be individually saved and
+// retrieved.
+//
+// Any item stored in the Pool may be removed automatically at any time without
+// notification. If the Pool holds the only reference when this happens, the
+// item might be deallocated.
+//
+// A Pool is safe for use by multiple goroutines simultaneously.
+//
+// Pool's purpose is to cache allocated but unused items for later reuse,
+// relieving pressure on the garbage collector. That is, it makes it easy to
+// build efficient, thread-safe free lists. However, it is not suitable for all
+// free lists.
+//
+// An appropriate use of a Pool is to manage a group of temporary items
+// silently shared among and potentially reused by concurrent independent
+// clients of a package. Pool provides a way to amortize allocation overhead
+// across many clients.
+//
+// An example of good use of a Pool is in the fmt package, which maintains a
+// dynamically-sized store of temporary output buffers. The store scales under
+// load (when many goroutines are actively printing) and shrinks when
+// quiescent.
+//
+// On the other hand, a free list maintained as part of a short-lived object is
+// not a suitable use for a Pool, since the overhead does not amortize well in
+// that scenario. It is more efficient to have such objects implement their own
+// free list.
+//
+// A Pool must not be copied after first use.
+//
+// In the terminology of [the Go memory model], a call to Put(x) “synchronizes before”
+// a call to [Pool.Get] returning that same value x.
+// Similarly, a call to New returning x “synchronizes before”
+// a call to Get returning that same value x.
+//
+// [the Go memory model]: https://go.dev/ref/mem
+type Pool struct {
+	noCopy noCopy
+
+	local     unsafe.Pointer // local fixed-size per-P pool, actual type is [P]poolLocal
+	localSize uintptr        // size of the local array
+
+	victim     unsafe.Pointer // local from previous cycle
+	victimSize uintptr        // size of victims array
+
+	// New optionally specifies a function to generate
+	// a value when Get would otherwise return nil.
+	// It may not be changed concurrently with calls to Get.
+	New  func() any
+	once sync.Once
+}
+
+// Local per-P Pool appendix.
+type poolLocalInternal struct {
+	private any       // Can be used only by the respective P.
+	shared  poolChain // Local P can pushHead/popHead; any P can popTail.
+}
+
+type poolLocal struct {
+	poolLocalInternal
+
+	// Prevents false sharing on widespread platforms with
+	// 128 mod (cache line size) = 0 .
+	pad [128 - unsafe.Sizeof(poolLocalInternal{})%128]byte
+}
+
+// Put adds x to the pool.
+func (p *Pool) Put(x any) {
+	if x == nil {
+		return
+	}
+	l, _ := p.pin()
+	if l.private == nil {
+		l.private = x
+	} else {
+		l.shared.pushHead(x)
+	}
+}
+
+// Get selects an arbitrary item from the [Pool], removes it from the
+// Pool, and returns it to the caller.
+// Get may choose to ignore the pool and treat it as empty.
+// Callers should not assume any relation between values passed to [Pool.Put] and
+// the values returned by Get.
+//
+// If Get would otherwise return nil and p.New is non-nil, Get returns
+// the result of calling p.New.
+func (p *Pool) Get() any {
+	l, _ := p.pin()
+	x := l.private
+	l.private = nil
+	if x == nil {
+		x, _ = l.shared.popHead()
+		if x == nil {
+			x = p.getSlow(0)
+		}
+	}
+	if x == nil && p.New != nil {
+		x = p.New()
+	}
+	return x
+}
+
+// pin pins the current goroutine to P, disables preemption and
+// returns poolLocal pool for the P and the P's id.
+// Caller must call runtime_procUnpin() when done with the pool.
+func (p *Pool) pin() (*poolLocal, int) {
+	// Check whether p is nil to get a panic.
+	// Otherwise the nil dereference happens while the m is pinned,
+	// causing a fatal error rather than a panic.
+	if p == nil {
+		panic("nil Pool")
+	}
+
+	if ptr := atomic.LoadPointer(&p.local); ptr != nil {
+		handle := (*tls.Handle[*poolLocal])(ptr)
+		l := handle.Get()
+		if l == nil {
+			l = &poolLocal{}
+			handle.Set(l)
+		}
+		return l, 0
+	}
+
+	return p.pinSlow()
+}
+
+func (p *Pool) pinSlow() (*poolLocal, int) {
+	p.once.Do(func() {
+		handle := tls.Alloc[*poolLocal](func(head **poolLocal) {
+			if head != nil {
+				atomic.StorePointer(&p.victim, unsafe.Pointer(*head))
+			}
+		})
+		atomic.StorePointer(&p.local, unsafe.Pointer(&handle))
+	})
+	handle := (*tls.Handle[*poolLocal])(p.local)
+	l := &poolLocal{}
+	handle.Set(l)
+	return l, 0
+}
+
+func (p *Pool) getSlow(pid int) any {
+	if ptr := atomic.LoadPointer(&p.victim); ptr != nil {
+		l := (*poolLocal)(ptr)
+		if x := l.private; x != nil {
+			l.private = nil
+			return x
+		}
+		if x, _ := l.shared.popTail(); x != nil {
+			return x
+		}
+		atomic.StorePointer(&p.victim, nil)
+	}
+	return nil
+}
+
+// noCopy may be added to structs which must not be copied
+// after the first use.
+//
+// See https://golang.org/issues/8005#issuecomment-190753527
+// for details.
+//
+// Note that it must not be embedded, due to the Lock and Unlock methods.
+type noCopy struct{}
+
+// Lock is a no-op used by -copylocks checker from `go vet`.
+func (*noCopy) Lock()   {}
+func (*noCopy) Unlock() {}
diff --git a/runtime/internal/lib/sync/poolqueue.go b/runtime/internal/lib/sync/poolqueue.go
new file mode 100644
index 0000000000..e9593f8c44
--- /dev/null
+++ b/runtime/internal/lib/sync/poolqueue.go
@@ -0,0 +1,302 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sync
+
+import (
+	"sync/atomic"
+	"unsafe"
+)
+
+// poolDequeue is a lock-free fixed-size single-producer,
+// multi-consumer queue. The single producer can both push and pop
+// from the head, and consumers can pop from the tail.
+//
+// It has the added feature that it nils out unused slots to avoid
+// unnecessary retention of objects. This is important for sync.Pool,
+// but not typically a property considered in the literature.
+type poolDequeue struct {
+	// headTail packs together a 32-bit head index and a 32-bit
+	// tail index. Both are indexes into vals modulo len(vals)-1.
+	//
+	// tail = index of oldest data in queue
+	// head = index of next slot to fill
+	//
+	// Slots in the range [tail, head) are owned by consumers.
+	// A consumer continues to own a slot outside this range until
+	// it nils the slot, at which point ownership passes to the
+	// producer.
+	//
+	// The head index is stored in the most-significant bits so
+	// that we can atomically add to it and the overflow is
+	// harmless.
+	headTail atomic.Uint64
+
+	// vals is a ring buffer of interface{} values stored in this
+	// dequeue. The size of this must be a power of 2.
+	//
+	// vals[i].typ is nil if the slot is empty and non-nil
+	// otherwise. A slot is still in use until *both* the tail
+	// index has moved beyond it and typ has been set to nil. This
+	// is set to nil atomically by the consumer and read
+	// atomically by the producer.
+	vals []eface
+}
+
+type eface struct {
+	typ, val unsafe.Pointer
+}
+
+const dequeueBits = 32
+
+// dequeueLimit is the maximum size of a poolDequeue.
+//
+// This must be at most (1<<dequeueBits)/2 because detecting fullness
+// depends on wrapping around the ring buffer without wrapping around
+// the index. We divide by 4 so this fits in an int on 32-bit.
+const dequeueLimit = (1 << dequeueBits) / 4
+
+// dequeueNil is used in poolDequeue to represent interface{}(nil).
+// Since we use nil to represent empty slots, we need a sentinel value
+// to represent nil.
+type dequeueNil *struct{}
+
+func (d *poolDequeue) unpack(ptrs uint64) (head, tail uint32) {
+	const mask = 1<<dequeueBits - 1
+	head = uint32((ptrs >> dequeueBits) & mask)
+	tail = uint32(ptrs & mask)
+	return
+}
+
+func (d *poolDequeue) pack(head, tail uint32) uint64 {
+	const mask = 1<<dequeueBits - 1
+	return (uint64(head) << dequeueBits) |
+		uint64(tail&mask)
+}
+
+// pushHead adds val at the head of the queue. It returns false if the
+// queue is full. It must only be called by a single producer.
+func (d *poolDequeue) pushHead(val any) bool {
+	ptrs := d.headTail.Load()
+	head, tail := d.unpack(ptrs)
+	if (tail+uint32(len(d.vals)))&(1<<dequeueBits-1) == head {
+		// Queue is full.
+		return false
+	}
+	slot := &d.vals[head&uint32(len(d.vals)-1)]
+
+	// Check if the head slot has been released by popTail.
+	typ := atomic.LoadPointer(&slot.typ)
+	if typ != nil {
+		// Another goroutine is still cleaning up the tail, so
+		// the queue is actually still full.
+		return false
+	}
+
+	// The head slot is free, so we own it.
+	if val == nil {
+		val = dequeueNil(nil)
+	}
+	*(*any)(unsafe.Pointer(slot)) = val
+
+	// Increment head. This passes ownership of slot to popTail
+	// and acts as a store barrier for writing the slot.
+	d.headTail.Add(1 << dequeueBits)
+	return true
+}
+
+// popHead removes and returns the element at the head of the queue.
+// It returns false if the queue is empty. It must only be called by a
+// single producer.
+func (d *poolDequeue) popHead() (any, bool) {
+	var slot *eface
+	for {
+		ptrs := d.headTail.Load()
+		head, tail := d.unpack(ptrs)
+		if tail == head {
+			// Queue is empty.
+			return nil, false
+		}
+
+		// Confirm tail and decrement head. We do this before
+		// reading the value to take back ownership of this
+		// slot.
+		head--
+		ptrs2 := d.pack(head, tail)
+		if d.headTail.CompareAndSwap(ptrs, ptrs2) {
+			// We successfully took back slot.
+			slot = &d.vals[head&uint32(len(d.vals)-1)]
+			break
+		}
+	}
+
+	val := *(*any)(unsafe.Pointer(slot))
+	if val == dequeueNil(nil) {
+		val = nil
+	}
+	// Zero the slot. Unlike popTail, this isn't racing with
+	// pushHead, so we don't need to be careful here.
+	*slot = eface{}
+	return val, true
+}
+
+// popTail removes and returns the element at the tail of the queue.
+// It returns false if the queue is empty. It may be called by any
+// number of consumers.
+func (d *poolDequeue) popTail() (any, bool) {
+	var slot *eface
+	for {
+		ptrs := d.headTail.Load()
+		head, tail := d.unpack(ptrs)
+		if tail == head {
+			// Queue is empty.
+			return nil, false
+		}
+
+		// Confirm head and tail (for our speculative check
+		// above) and increment tail. If this succeeds, then
+		// we own the slot at tail.
+		ptrs2 := d.pack(head, tail+1)
+		if d.headTail.CompareAndSwap(ptrs, ptrs2) {
+			// Success.
+			slot = &d.vals[tail&uint32(len(d.vals)-1)]
+			break
+		}
+	}
+
+	// We now own slot.
+	val := *(*any)(unsafe.Pointer(slot))
+	if val == dequeueNil(nil) {
+		val = nil
+	}
+
+	// Tell pushHead that we're done with this slot. Zeroing the
+	// slot is also important so we don't leave behind references
+	// that could keep this object live longer than necessary.
+	//
+	// We write to val first and then publish that we're done with
+	// this slot by atomically writing to typ.
+	slot.val = nil
+	atomic.StorePointer(&slot.typ, nil)
+	// At this point pushHead owns the slot.
+
+	return val, true
+}
+
+// poolChain is a dynamically-sized version of poolDequeue.
+//
+// This is implemented as a doubly-linked list queue of poolDequeues
+// where each dequeue is double the size of the previous one. Once a
+// dequeue fills up, this allocates a new one and only ever pushes to
+// the latest dequeue. Pops happen from the other end of the list and
+// once a dequeue is exhausted, it gets removed from the list.
+type poolChain struct {
+	// head is the poolDequeue to push to. This is only accessed
+	// by the producer, so doesn't need to be synchronized.
+	head *poolChainElt
+
+	// tail is the poolDequeue to popTail from. This is accessed
+	// by consumers, so reads and writes must be atomic.
+	tail atomic.Pointer[poolChainElt]
+}
+
+type poolChainElt struct {
+	poolDequeue
+
+	// next and prev link to the adjacent poolChainElts in this
+	// poolChain.
+	//
+	// next is written atomically by the producer and read
+	// atomically by the consumer. It only transitions from nil to
+	// non-nil.
+	//
+	// prev is written atomically by the consumer and read
+	// atomically by the producer. It only transitions from
+	// non-nil to nil.
+	next, prev atomic.Pointer[poolChainElt]
+}
+
+func (c *poolChain) pushHead(val any) {
+	d := c.head
+	if d == nil {
+		// Initialize the chain.
+		const initSize = 8 // Must be a power of 2
+		d = new(poolChainElt)
+		d.vals = make([]eface, initSize)
+		c.head = d
+		c.tail.Store(d)
+	}
+
+	if d.pushHead(val) {
+		return
+	}
+
+	// The current dequeue is full. Allocate a new one of twice
+	// the size.
+	newSize := len(d.vals) * 2
+	if newSize >= dequeueLimit {
+		// Can't make it any bigger.
+		newSize = dequeueLimit
+	}
+
+	d2 := &poolChainElt{}
+	d2.prev.Store(d)
+	d2.vals = make([]eface, newSize)
+	c.head = d2
+	d.next.Store(d2)
+	d2.pushHead(val)
+}
+
+func (c *poolChain) popHead() (any, bool) {
+	d := c.head
+	for d != nil {
+		if val, ok := d.popHead(); ok {
+			return val, ok
+		}
+		// There may still be unconsumed elements in the
+		// previous dequeue, so try backing up.
+		d = d.prev.Load()
+	}
+	return nil, false
+}
+
+func (c *poolChain) popTail() (any, bool) {
+	d := c.tail.Load()
+	if d == nil {
+		return nil, false
+	}
+
+	for {
+		// It's important that we load the next pointer
+		// *before* popping the tail. In general, d may be
+		// transiently empty, but if next is non-nil before
+		// the pop and the pop fails, then d is permanently
+		// empty, which is the only condition under which it's
+		// safe to drop d from the chain.
+		d2 := d.next.Load()
+
+		if val, ok := d.popTail(); ok {
+			return val, ok
+		}
+
+		if d2 == nil {
+			// This is the only dequeue. It's empty right
+			// now, but could be pushed to in the future.
+			return nil, false
+		}
+
+		// The tail of the chain has been drained, so move on
+		// to the next dequeue. Try to drop it from the chain
+		// so the next pop doesn't have to look at the empty
+		// dequeue again.
+		if c.tail.CompareAndSwap(d, d2) {
+			// We won the race. Clear the prev pointer so
+			// the garbage collector can collect the empty
+			// dequeue and so popHead doesn't back up
+			// further than necessary.
+			d2.prev.Store(nil)
+		}
+		d = d2
+	}
+}