This patch enables sharing of an nsAttrValue's MiscContainer between nodes for style rules. MiscContainers of type eCSSStyleRule are now refcounted (with some clever struct packing to ensure that the amount of memory allocated for MiscContainer remains unchanged on 32 and 64 bit). This infrastructure can be used to share most MiscContainer types in the future if we find advantages to sharing other types than just eCSSStyleRuley. A cache mapping strings to MiscContainers has been added to nsHTMLCSSStyleSheet. MiscContainers can be shared between nsAttrValues when one nsAttrValue is SetTo another nsAttrValue or when there is a cache hit in this cache. This patch also adds the ability to tell a style rule that it belongs to an nsHTMLCSSStyleSheet, with appropriate accessor functions to separate that from the existing case of belonging to an nsCSSStyleSheet.
The primary use case is to reduce memory use for pages that have lots of inline style attributes with the same value. This can happen easily with large pages that are automatically generated. An (admittedly pathological) testcase in Bug 686975 sees over 250 MB of memory savings with this change. Reusing the same MiscContainer for multiple nodes saves the overhead of maintaining separate copies of the string containing the serialized value of the style attribute and of creating separate style rules for each node. Eliminating duplicate style rules enables further savings in layout through style context sharing. The testcase sees the amount of memory used by style contexts go from over 250 MB to 10 KB.
Because the cache is based on the text value of the style attribute, it will not handle attributes that have different text values but are parsed into identical style rules. We also do not attempt to share MiscContainers when the node's base URI differs from the document URI. The effect of these limitations is expected to be low.
This is the full implementation of the AudioBuffer object. There are
two ways to create these objects from an audio context and this patch
implements only one of them.
The construction of the AudioBuffer object is a two step process: the
object should be created with operator new first, and then
InitializeBuffers should be called on it. InitializeBuffers is
fallible, because it uses the JS API to create the underlying typed
arrays, but that's fine, since the length of the buffers comes from web
content, and we don't want to use infallible allocations for those
anyways.
We hold on to the JS objects from the C++ implementation, and trace
through all of those objects, so that a GC does not kill those object
without us knowing.
The buffer should be possible to manipulate from both C++ and JS, and
the C++ object probably needs to support a set of methods for the C++
callers at some point.
This is the bare minimum that one needs in order to get those interfaces
implemented. The work to make the simplest of Web Audio test cases
actually pass will be done in bug 792649.
This is the bare minimum that one needs in order to get those interfaces
implemented. The work to make the simplest of Web Audio test cases
actually pass will be done in bug 792649.
The valid annotations are [Throws], [GetterThrows], and [SetterThrows], which can all either take no value or
be set to MainThread or Workers if the throwing behavior is only happening on main thread or in workers
