Update addons.markdown

[ghost]

Updates addons.markdown to mention AtExit() function. Addresses issue #8324.

[chrisdickinson]

This might be best phrased as "Registers exit hooks that run after the event loop has ended, but before the VM is killed." Also, it would be good to include the arguments, argument types, and a quick code example of how you might
use the function.

[sam-github]

AtExit functions only run in vm, not when main node is exiting?

[chrisdickinson]

@sam-github the documentation is pulled from the text of the commit that introduces the function -- I think it runs right before the process ends.

[ghost]

How about:

Registers exit hooks that run after the event loop has ended, but before the VM is killed.
Callbacks are run in reverse order of registration, i.e. newest first. AtExit takes callback
and its arguments as arguments. See implementation below:

 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;
 }

The file binding.cc implements AtExit below:

 #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 in JavaScript by running:

 var binding = require('./build/Release/binding');

[chrisdickinson]

@sjsharp great work! The only other thing I'd add is a list of the arguments after the function definition -- something like we do for javascript:

### void AtExit(callback, args)

* `callback`: `void (*)(void*)` - A pointer to the function to call at exit.
* `args`: `void*` - A pointer to pass to the callback at exit.

[ghost]

Like this?

void AtExit(callback, args)

• callback: void (*)(void*) - A pointer to the function to call at exit.
• args: void* - A pointer to pass to the callback at exit.

Registers exit hooks that run after the event loop has ended, but before the VM is killed.

Callbacks are run in reverse order of registration, i.e. newest first. AtExit takes callback
and its arguments as arguments. See implementation below:

  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;
  }

The file binding.cc implements AtExit below:

  #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 in JavaScript by running:

  var binding = require('./build/Release/binding');

[indutny]

Yep, looking good.

[ghost]

Pushed changes to patch-1 branch on sjsharp/node.

[trevnorris]

Run make test-addon and ensure all tests pass please.

[trevnorris]

Future note to whoever merges this: Add the following in the commit message:

Fixes: https://github.com/joyent/node/issues/8324

[JCMais]

What is the status here? Why it was not merged?

This function is very handy for addons to cleanup resources, and it's still undocumented.

[trevnorris]

IIRC it was because it make test-addon failed with this patch, but no one from core closed this issue. We were simply waiting for the patch to be fixed.