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How would I overload the message passing system such that I...

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Question by John
Submitted on 6/28/2004
Related FAQ: Objective-C FAQ
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How would I overload the message passing system such that I could extend the functionality of it to automatically handle swizzling of an object with proper locking for a thread safe environment?  I can handle the locking, just can't figure out how to hack the message passing functions.

It would appear as such:

void new_message_passing_code(id anObject, void *result, ...) {
  va_list *a = va_start(result);
  int lockHeld = 0;
  if (anObject)
    lockHeld = [anObject readLockAccess];
  if (lockHeld) {
    vnew_message_passing_code([anObject replacer], result, a);
  else {
    old_message_passer(anObject, result, a);
  if (anObject)
    [anObject unlockAccess];

Or something.  I don't know how the system works, but it'd look like that (with vnew_... being the same, with a va_list).

The point would be that I could lock an access lock on an object, and have a special member switch the object out for a new one and set the internal pointer for the old one to the new one; then if that switch is detected, it will redirect the message search to the new object, thus creating a thread-safe method of exchanging any object for any other object from a simple plugin interface.

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