Thanks for asking about this; we have a lot of unnecessary unlinking code in our JS,
Let me share how I investigated your question. $ git grep -i addmessagelistener -- '*.cpp' content/base/src/nsFrameMessageManager.cpp:nsFrameMessageManager::AddMessageListener(const nsAString& aMessage, Only one hit; that's easy. Looking at the function, message listeners are stored in nsFrameMessageManager::mListeners. So what's the lifetime of that array? The array is cleared in a few places: 1) nsFrameMessageManager::Disconnect(), 2) MMListenerRemover::~MMListenerRemover 3) nsFrameMessageManager's CC unlink function, It looks like (2) is just a way of delaying Disconnect()'s removal until message handling is complete. So when do we call Disconnect()? http://dxr.mozilla.org/mozilla-central/search?q=%2Bcallers%3AnsFrameMessageManager%3A%3ADisconnect%28_Bool%29 At this point it's clear that we /attempt/ to clear the message listeners when the message manager's window goes away. That's probably as far as you'd get by asking someone. Whether or not we totally succeed in this endeavor is another question entirely. You could instrument your build to count the number of live nsFrameMessageManager objects and report the number of message listeners in each -- one way to do this would be with a patch very similar to this one [1]. [1] https://bug893242.bugzilla.mozilla.org/attachment.cgi?id=774978 On Thu, Jul 25, 2013 at 6:51 PM, Mark Hammond <[email protected]> wrote: > Felipe and I were having a discussion around a patch that uses > nsIMessageManager. Specifically, we create a <browser> element, then call > browser.messageManager.addMessageListener() with the requirement that the > listener live for as long as the browser element itself. > > The question we had was whether it was necessary to explicitly call > removeMessageListener, or whether we can rely on automatic cleanup when the > browser element dies? It seems obvious to us that it *should* be safe to > rely on automatic cleanup, but searching both docs and mxr didn't make it > clear, so I figured it was better to ask rather than to cargo-cult the > addition of explicit cleanup code that wasn't necessary. > > Thanks, > > Mark > _______________________________________________ > dev-platform mailing list > [email protected] > https://lists.mozilla.org/listinfo/dev-platform _______________________________________________ dev-platform mailing list [email protected] https://lists.mozilla.org/listinfo/dev-platform
