diff --git a/list.h b/list.h
index 0a1bc5a49..c9be5de7d 100644
--- a/list.h
+++ b/list.h
@@ -45,6 +45,11 @@ static inline void init_list_head(struct list_head *head)
     head->next = head;
 }
 
+static inline int list_empty(const struct list_head *el)
+{
+    return el->next == el;
+}
+
 /* insert 'el' between 'prev' and 'next' */
 static inline void __list_add(struct list_head *el, 
                               struct list_head *prev, struct list_head *next)
@@ -67,6 +72,20 @@ static inline void list_add_tail(struct list_head *el, struct list_head *head)
     __list_add(el, head->prev, head);
 }
 
+static inline void list_splice(const struct list_head *list,
+                               struct list_head *head)
+{
+    if (!list_empty(list)) {
+        struct list_head *a = list->next;
+        struct list_head *b = list->prev;
+        struct list_head *c = head->next;
+        head->next = a;
+        a->prev = head;
+        b->next = c;
+        c->prev = b;
+    }
+}
+
 static inline void list_del(struct list_head *el)
 {
     struct list_head *prev, *next;
@@ -78,11 +97,6 @@ static inline void list_del(struct list_head *el)
     el->next = NULL; /* fail safe */
 }
 
-static inline int list_empty(struct list_head *el)
-{
-    return el->next == el;
-}
-
 #define list_for_each(el, head) \
   for(el = (head)->next; el != (head); el = el->next)
 
diff --git a/quickjs.c b/quickjs.c
index 0e28e7311..db4a8d01f 100644
--- a/quickjs.c
+++ b/quickjs.c
@@ -308,6 +308,13 @@ struct JSRuntime {
     void *user_opaque;
 };
 
+typedef struct JSRuntimeInternalThreadState {
+    uintptr_t stack_top;
+    JSValue current_exception;
+    struct JSStackFrame *current_stack_frame;
+    struct list_head job_list;
+} JSRuntimeInternalThreadState;
+
 struct JSClass {
     uint32_t class_id; /* 0 means free entry */
     JSAtom class_name;
@@ -1769,6 +1776,42 @@ JSRuntime *JS_NewRuntime(void)
     return JS_NewRuntime2(&def_malloc_funcs, NULL);
 }
 
+void JS_Enter(JSRuntime *rt)
+{
+    rt->stack_top = js_get_stack_pointer();
+}
+
+void JS_Suspend(JSRuntime *rt, JSRuntimeThreadState *state)
+{
+    JSRuntimeInternalThreadState *s = (JSRuntimeInternalThreadState *)state;
+
+    s->stack_top = rt->stack_top;
+    s->current_exception = rt->current_exception;
+    s->current_stack_frame = rt->current_stack_frame;
+    memcpy(&s->job_list, &rt->job_list, sizeof(rt->job_list));
+
+    rt->stack_top = 0;
+    rt->current_exception = JS_NULL;
+    rt->current_stack_frame = NULL;
+    init_list_head(&rt->job_list);
+}
+
+void JS_Resume(JSRuntime *rt, const JSRuntimeThreadState *state)
+{
+    const JSRuntimeInternalThreadState *s =
+        (const JSRuntimeInternalThreadState *)state;
+
+    rt->stack_top = s->stack_top;
+    rt->current_exception = s->current_exception;
+    rt->current_stack_frame = s->current_stack_frame;
+    list_splice(&s->job_list, &rt->job_list);
+}
+
+void JS_Leave(JSRuntime *rt)
+{
+    rt->stack_top = 0;
+}
+
 void JS_SetMemoryLimit(JSRuntime *rt, size_t limit)
 {
     rt->malloc_state.malloc_limit = limit;
diff --git a/quickjs.h b/quickjs.h
index d4a5cd311..816f848d5 100644
--- a/quickjs.h
+++ b/quickjs.h
@@ -312,6 +312,10 @@ typedef JSValue JSCFunction(JSContext *ctx, JSValueConst this_val, int argc, JSV
 typedef JSValue JSCFunctionMagic(JSContext *ctx, JSValueConst this_val, int argc, JSValueConst *argv, int magic);
 typedef JSValue JSCFunctionData(JSContext *ctx, JSValueConst this_val, int argc, JSValueConst *argv, int magic, JSValue *func_data);
 
+typedef struct JSRuntimeThreadState {
+    char data[64];
+} JSRuntimeThreadState;
+
 typedef struct JSMallocState {
     size_t malloc_count;
     size_t malloc_size;
@@ -329,6 +333,10 @@ typedef struct JSMallocFunctions {
 typedef struct JSGCObjectHeader JSGCObjectHeader;
 
 JSRuntime *JS_NewRuntime(void);
+void JS_Enter(JSRuntime *rt);
+void JS_Suspend(JSRuntime *rt, JSRuntimeThreadState *state);
+void JS_Resume(JSRuntime *rt, const JSRuntimeThreadState *state);
+void JS_Leave(JSRuntime *rt);
 /* info lifetime must exceed that of rt */
 void JS_SetRuntimeInfo(JSRuntime *rt, const char *info);
 void JS_SetMemoryLimit(JSRuntime *rt, size_t limit);