Changes between Version 2 and Version 3 of Abandoned documents

Timestamp:

Aug 18, 2018 1:04:57 PM (6 years ago)

Author:

Simon Fraser

Comment:

--

Abandoned documents

@@ -7 +7 @@
 = Why are layout test results showing me a list of abandoned documents? =
 
-Because leaked documents usually entrain a lot of other objects, which can use lots of memory (e.g. via entries in the memory cache). Leaking documents is bad because it will cause ever-increasing memory use as the user browses. See [https://bugs.webkit.org/show_bug.cgi?id=186214]
+Leaked documents usually entrain a lot of other objects, which can use lots of memory (e.g. via entries in the memory cache). Leaking documents is bad because it will cause ever-increasing memory use as the user browses. See [https://bugs.webkit.org/show_bug.cgi?id=186214]
 
 = What should I do if see a new case of document abandonment? =
 
 If you made a code change that is causing a test to newly show that a document is leaked, it probably means you have a coding bug that is triggered a leak or (more likely) a reference cycle. You need to resolve this before committing.
+
+= How do I debug document abandonment? =
+
+Let's take an example [https://bugs.webkit.org/show_bug.cgi?id=188722]. We run tests, checking for abandonment:
+
+{{{
+run-webkit-tests fast/forms/ --check-for-abandoned-documents
+}}}
+
+The results say that {{{fast/forms/textarea-paste-newline.html}}} was abandoned. Now you have to figure out why this Document object is not going away.
+
+A bit of testing in MiniBrowser can be useful, and if you're lucky, the abandonment will reproduce there. To test this, do these steps:
+1. Run MiniBrowser
+2. Load a simple HTML file (not the test!)
+3. Load the test file
+4. Go back to the simple HTML file
+5. Simulate a memory warning (on macOS, you can do this by running {{{notifyutil -p "org.WebKit.lowMemory"}}} in the Terminal).
+6. Now dump the list of live documents: {{{notifyutil -p "com.apple.WebKit.showAllDocuments"}}}. This will show something like:
+{{{
+2 live documents:
+Document 0x630002400 (refCount 5, referencingNodeCount 1) file:///Volumes/Data/webkit/LayoutTests/fast/forms/textarea-paste-newline.html
+Document 0x630024400 (refCount 2, referencingNodeCount 4) file:///Volumes/Data/simple.html
+}}}
+7. That confirms that after a memory warning (which clears caches and does a GC) that the document is still alive. So something is holding a reference to it.