Xuân Baldauf Reporter
	Description • 9 years ago

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:42.0) Gecko/20100101 Firefox/42.0 SeaMonkey/2.39
Build ID: 2015110400

Steps to reproduce:

Each time a tab is closed (or an empty tab's document is replaced by a different document due to the user navigating), a WindowDestroyedEvent is created.

When handling the WindowDestroyedEvent, method js::NukeCrossCompartmentWrappers() is called (see
http://hg.mozilla.org/releases/mozilla-release/annotate/6fd87bafc499/dom/base/nsGlobalWindow.cpp#l9214 )

This method iterates over all compartments (that effectively means: all tabs), and for each interesting compartments, it iterates over all wrappers in that compartment (see http://hg.mozilla.org/releases/mozilla-release/annotate/6fd87bafc499/js/src/proxy/CrossCompartmentWrapper.cpp#l451 )

So effectively, opening or closing one tab takes Ω(n) time. An action where all tabs are opened (e.g. during session restore) thus takes Ω(n²) time.

Thus, the current firefox does not scale, while it should.


Actual results:

See these stack traces:

When a tab is closed, then this happens:

nsGlobalWindow::NotifyWindowIDDestroyed dom/base/nsGlobalWindow.cpp:9234
nsGlobalWindow::FreeInnerObjects        dom/base/nsGlobalWindow.cpp:1632
nsGlobalWindow::DetachFromDocShell	    dom/base/nsGlobalWindow.cpp:2897
nsDocShell::Destroy                     docshell/base/nsDocShell.cpp:5715
nsFrameLoader::DestroyDocShell          dom/base/nsFrameLoader.cpp:1473
nsFrameLoaderDestroyRunnable::Run       dom/base/nsFrameLoader.cpp:1411

When a tab is opened, then this happens:

nsGlobalWindow::NotifyWindowIDDestroyed dom/base/nsGlobalWindow.cpp:9234
nsGlobalWindow::FreeInnerObjects        dom/base/nsGlobalWindow.cpp:1632
nsGlobalWindow::SetNewDocument          dom/base/nsGlobalWindow.cpp:2558
nsDocumentViewer::InitInternal          layout/base/nsDocumentViewer.cpp:881
nsDocumentViewer::Init                  layout/base/nsDocumentViewer.cpp:621
nsDocShell::SetupNewViewer              docshell/base/nsDocShell.cpp:9167
nsDocShell::Embed                       docshell/base/nsDocShell.cpp:7068
nsDocShell::CreateContentViewer         docshell/base/nsDocShell.cpp:8975
nsDSURIContentListener::DoContent       docshell/base/nsDSURIContentListener.cpp:129
nsDocumentOpenInfo::TryContentListener	uriloader/base/nsURILoader.cpp:725
nsDocumentOpenInfo::DispatchContent     uriloader/base/nsURILoader.cpp:398
nsDocumentOpenInfo::OnStartRequest      uriloader/base/nsURILoader.cpp:259
nsBaseChannel::OnStartRequest           netwerk/base/nsBaseChannel.cpp:784

In both cases, a WindowDestroyedEvent is created (see http://hg.mozilla.org/releases/mozilla-release/annotate/6fd87bafc499/dom/base/nsGlobalWindow.cpp#l9234)


Expected results:

Opening or closing one tab should take O(1) time, not O(n) time.
Maybe this can be achieved by keeping the wrappers even if their destination object does not exist anymore.

At least, restoring a session should take O(n) time, not O(n²) time.

	Simona Badau, Desktop QA
	Comment 1 • 9 years ago

This is very similar to Bug 816784.