addon: add AtExit() function

Lets native addons register exit hooks that run after the event loop has quit
but before the VM is killed.

Fixes #3147.

src/node.cc

@@ -2770,6 +2770,37 @@ char** Init(int argc, char *argv[]) {
 }
 
 
+struct AtExitCallback {
+  AtExitCallback* next_;
+  void (*cb_)(void* arg);
+  void* arg_;
+};
+
+static AtExitCallback* at_exit_functions_;
+
+
+void RunAtExit() {
+  AtExitCallback* p = at_exit_functions_;
+  at_exit_functions_ = NULL;
+
+  while (p) {
+    AtExitCallback* q = p->next_;
+    p->cb_(p->arg_);
+    delete p;
+    p = q;
+  }
+}
+
+
+void AtExit(void (*cb)(void* arg), void* arg) {
+  AtExitCallback* p = new AtExitCallback;
+  p->cb_ = cb;
+  p->arg_ = arg;
+  p->next_ = at_exit_functions_;
+  at_exit_functions_ = p;
+}
+
+
 void EmitExit(v8::Handle<v8::Object> process_l) {
   // process.emit('exit')
   process_l->Set(String::NewSymbol("_exiting"), True());
@@ -2850,6 +2881,7 @@ int Start(int argc, char *argv[]) {
   uv_run(uv_default_loop());
 
   EmitExit(process_l);
+  RunAtExit();
 
 #ifndef NDEBUG
   // Clean up.

src/node.h

@@ -250,6 +250,11 @@ node_module_struct* get_builtin_module(const char *name);
 #define NODE_MODULE_DECL(modname) \
   extern "C" node::node_module_struct modname ## _module;
 
+/* Called after the event loop exits but before the VM is disposed.
+ * Callbacks are run in reverse order of registration, i.e. newest first.
+ */
+NODE_EXTERN void AtExit(void (*cb)(void* arg), void* arg = 0);
+
 NODE_EXTERN void SetErrno(uv_err_t err);
 NODE_EXTERN v8::Handle<v8::Value>
 MakeCallback(const v8::Handle<v8::Object> object,

test/addons/at-exit/binding.cc

@@ -0,0 +1,43 @@
+#undef NDEBUG
+#include <assert.h>
+#include <stdlib.h>
+#include <node.h>
+#include <v8.h>
+
+using node::AtExit;
+using v8::Handle;
+using v8::HandleScope;
+using v8::Local;
+using v8::Object;
+
+static char cookie[] = "yum yum";
+static int at_exit_cb1_called = 0;
+static int at_exit_cb2_called = 0;
+
+static void at_exit_cb1(void* arg) {
+  HandleScope scope;
+  assert(arg == 0);
+  Local<Object> obj = Object::New();
+  assert(!obj.IsEmpty()); // assert VM is still alive
+  assert(obj->IsObject());
+  at_exit_cb1_called++;
+}
+
+static void at_exit_cb2(void* arg) {
+  assert(arg == static_cast<void*>(cookie));
+  at_exit_cb2_called++;
+}
+
+static void sanity_check(void) {
+  assert(at_exit_cb1_called == 1);
+  assert(at_exit_cb2_called == 2);
+}
+
+void init(Handle<Object> target) {
+  AtExit(at_exit_cb1);
+  AtExit(at_exit_cb2, cookie);
+  AtExit(at_exit_cb2, cookie);
+  atexit(sanity_check);
+}
+
+NODE_MODULE(binding, init);

test/addons/at-exit/binding.gyp

@@ -0,0 +1,8 @@
+{
+  'targets': [
+    {
+      'target_name': 'binding',
+      'sources': [ 'binding.cc' ]
+    }
+  ]
+}

test/addons/at-exit/test.js

@@ -0,0 +1 @@
+var binding = require('./build/Release/binding');