Remove ResourceFetcher's access to a real FetchContext at frame detach time

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index c6e912b0d03c784075c329c1390c3d6b8f960285..f0a44706efccb52dd8a34a0deb45f80ab64baff5 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -481,11 +481,13 @@ Document::Document(const DocumentInit& initializer, DocumentClassFlags documentC
         provideContextFeaturesToDocumentFrom(*this, *m_frame->page());
 
         m_fetcher = m_frame->loader().documentLoader()->fetcher();
-    }
-
-    if (!m_fetcher)
+        FrameFetchContext::provideDocumentToContext(m_fetcher->context(), this);
+    } else if (m_importsController) {
         m_fetcher = FrameFetchContext::createContextAndFetcher(nullptr);
-    static_cast<FrameFetchContext&>(m_fetcher->context()).setDocument(this);
+        FrameFetchContext::provideDocumentToContext(m_fetcher->context(), this);
+    } else {
+        m_fetcher = ResourceFetcher::create(nullptr);
+    }
 
     // We depend on the url getting immediately set in subframes, but we
     // also depend on the url NOT getting immediately set in opened windows.
@@ -527,6 +529,7 @@ Document::~Document()
 {
     ASSERT(!layoutView());
     ASSERT(!parentTreeScope());
+    ASSERT(!m_importsController);

[sof, 2015/04/03 14:24:01]

Could you move this into the !ENABLE(OILPAN) section? We cannot guarantee that
it has been cleared with oilpan.

As to just removing the controller in detach(), let's try -- I don't see a code
path with non-Oilpan where that won't be sufficient.

[Nate Chapin, 2015/04/03 23:01:09]

Doesn't HTMLImportsController::removeFrom() call
Document::setImportsController(nullptr)?

[sof, 2015/04/04 06:42:15]

It does. But as stated previously, we cannot assume that Document::detach() has
run with Oilpan. 

 #if !ENABLE(OILPAN)
     ASSERT(m_ranges.isEmpty());
     ASSERT(!hasGuardRefCount());
@@ -564,9 +567,6 @@ Document::~Document()
     if (m_styleSheetList)
         m_styleSheetList->detachFromDocument();
 
-    if (m_importsController)
-        HTMLImportsController::removeFrom(*this);
-
     m_timeline->detachFromDocument();
 
     // We need to destroy CSSFontSelector before destroying m_fetcher.
@@ -575,13 +575,6 @@ Document::~Document()
     if (m_elemSheet)
         m_elemSheet->clearOwnerNode();
 
-    // It's possible for multiple Documents to end up referencing the same ResourceFetcher (e.g., SVGImages
-    // load the initial empty document and the SVGDocument with the same DocumentLoader).
-    FrameFetchContext& context = static_cast<FrameFetchContext&>(m_fetcher->context());
-    if (context.document() == this)
-        context.setDocument(nullptr);
-    m_fetcher.clear();
-
     // We must call clearRareData() here since a Document class inherits TreeScope
     // as well as Node. See a comment on TreeScope.h for the reason.
     if (hasRareData())
@@ -621,9 +614,6 @@ void Document::dispose()
 
     m_registrationContext.clear();
 
-    if (m_importsController)
-        HTMLImportsController::removeFrom(*this);
-
     // removeDetachedChildren() doesn't always unregister IDs,
     // so tear down scope information upfront to avoid having stale references in the map.
     destroyTreeScopeData();
@@ -837,6 +827,8 @@ void Document::setImportsController(HTMLImportsController* controller)
 {
     ASSERT(!m_importsController || !controller);
     m_importsController = controller;
+    if (!m_importsController)
+        m_fetcher->clearContext();
 }
 
 HTMLImportLoader* Document::importLoader() const
@@ -2136,6 +2128,19 @@ void Document::detach(const AttachContext& context)
 
     frameHost()->eventHandlerRegistry().documentDetached(*this);
 
+    // If this Document is associated with a live DocumentLoader, the
+    // DocumentLoader will take care of clearing the FetchContext. Deferring
+    // to the DocumentLoader when possible also prevents prematurely clearing
+    // the context in the case where multiple Documents end up associated with
+    // a single DocumentLoader (e.g., navigating to a javascript: url).
+    if (!loader())
+        m_fetcher->clearContext();
+    // If this document is the master for an HTMLImportsController, sever that

[Nate Chapin, 2015/04/02 20:22:06]

Comment added to explain the rationale for detaching HTMLImportsController here.

I believe detach() is guaranteed to be called before dispose() or ~Document(),
so I've removed the removeFrom() calls in the #if !ENABLE(OILPAN) blocks in
those functions. This is now the only place removeFrom() is called.

[sof, 2015/04/03 14:24:01]

Good comment, thanks.

This will hasten the demise of HTMLImportLoaders attached via that controller
object, but I notice they don't tidily remove themselves as clients of the
document parser when doing so -- leaving dead references. cf. a fast/dom/custom/
test that's failing on the trybots. Could you tidy up that as well here (or
otherwise address)?

[Nate Chapin, 2015/04/03 23:01:09]

Added removeClient() in HTMLImportLoader::dispose(), that fixed the test
locally.

+    // relationship. This ensures that we don't leave import loads in flight,
+    // thinking they should have access to a valid frame when they don't.
+    if (m_importsController)
+        HTMLImportsController::removeFrom(*this);
+
     // This is required, as our LocalFrame might delete itself as soon as it detaches
     // us. However, this violates Node::detach() semantics, as it's never
     // possible to re-attach. Eventually Document::detach() should be renamed,