Re: [platform-debug-dev] Memory View Infrastructure Review: Part 1

["Mikhail Khodjaiants" <mikhailk@xxxxxxx>]

Hi,

We (QNX) have concerns regarding the UI portion of the proposed model.
The idea of contributed renderings is excellent, but having special views to 
present the standard renderings as ascii, decimal, etc is very unusual. 
Currently the Memory view presents the data using the hardcoded Hex 
rendering and allows only one tab (rendering) per memory block. Is there any 
reason for this? Why the default renderings defined for a particular memory 
block type can't be used to present the data?

I have also minor comments for the core part.
The "IExtendedMemoryBlockRetrieval" interface contains the "getPaddedString" 
method. Why this method is included in the core?
And the methods of the "IMemoryBlockListener" interface begin with uppercase 
letters.

Thanks, Mikhail
----- Original Message ----- 
From: "Darin Wright" <Darin_Wright@xxxxxxxxxx>
To: <platform-debug-dev@xxxxxxxxxxx>
Sent: Wednesday, October 06, 2004 3:36 PM
Subject: [platform-debug-dev] Memory View Infrastructure Review: Part 1


Samantha,

I have read/reviewed the support in org.eclipse.debug.core relating to the
memory view infrastructure: i.e. extension point, classes and interfaces.
I want to be sure that I have a clear understanding of the core
infrastructure before I move on to the UI portion of the infrastructure.
Since there may be other interested parties, I suggest we conduct the
review on this mailing list in an open fashion.

To start, here's my understanding of the "memory view model": Arbitrary
memory blocks can be retrieved from debuggees (this was always part of the
model). A memory block can be rendered in N different ways (N >= 0). A
memory block has a data type associated with it which defines the type of
data contained in the memory block - for example, character data,
numerical data, or image data. The types of memory are open ended and
client defined (however, the platform could provide some renderings for
common types such as ASCII). The monitoring of memory blocks can be
expensive (in terms of size and communication with a debuggee). Thus, a
memory block manager is used to manage actively monitored memory blocks.
Similarly, since the mapping of memory block types to possible renderings
is 1:N, there is a memory block rendering manager that manages the active
renderings of currently monitored memory blocks. A memory block
implementation can be responsible for change notification itself (i.e.
notification of changes in its bytes), or it can let the client (memory
view) manage/compute changes.

Here's a list of design issues that need to be considered (please let me
know your opinion):
* The memory renderings extension point uses the fully qualified name of a
Java class to identify types of memory blocks. This is used to bind memory
blocks to default renderings and available renderings. Using a class name
is fragile and inflexible (i.e. changing an implementation class name
breaks extension points). It is also complex since the current
implementation uses the class/interface hierarchy to determine all
renderings for a memory block. Instead we should define an additional
method IExtendedMemoryBlock.getMemoryBlockType(), which returns a string
uniquely identifying the memory block type (i.e. its content/data type).
Is there a reason that we need complexity of multiple inheritance to
define memory block types?
* There is confusion in the naming scheme for the memory renderings
extension point and implementation interfaces/classes. The extension point
is called "memoryRenderings", however the IMemoryRendering interface is an
actual instance of a rendering, not an extension. I think the "type
pattern" which is used commonly in the debug platform should also be used
here. That is, the extension point should be renamed to
"memoryRenderingTypes" to represent a class of renderings. Then, a memory
rendering type can have a factory to create renderings (instances) of its
type. IMemoryRendering will represent an actual rendering (as it does
now), and IMemoryRenderingInfo will be renamed to IMemoryRenderingType.
* The rendering_property element is a sub-element of a rendering element,
and it is thus redundant to specify a renderingId (it is inherent in the
rendering element it is a child of). The attribute should be removed. The
memory renderings manager treats the property elements as both top-level
elements and children elements when initializing extension point
information - but only one format should be allowed (i.e. only as a child
element of a rendering element).
* Memory blocks have an undocumented lifecycle (which should be
documented). The delete() method is called when the block is removed from
the memory block manager, but there is no corresponding init() when the
block is added (this method should be added, and to be consistent with
other lifecycle methods, delete() should be renamed to dispose()). Also
doc that memory blocks are automatically disposed (removed) from the
manager when their target terminates. Memory renderings have a similar
lifecycle that needs to be documented - i.e. renderings are automatically
removed for terminated targets, and for removed memory blocks. Should
renderings have lifecycle methods too?

Other questions:
* Are rendering properties optional in a rendering extension?
* What does it mean to use a default rendering factory for a rendering
extension? (Answer from reading code: it means that the rendering is
created with the same memory block as the original. I suppose this means
that a factory can change the bytes in the memory block? Is that the sole
purpose of a rendering factory?)
* The factory specified for hex renderings is ill-specified in plug-in XML
? it refers to a non-existant class
(org.eclipse.debug.internal.ui.views.memoryHexRenderingFactory - note the
missing "." between memory and HexRenderingFactory). This means the
default factory is being used. However the rendering that the hex factory
creates (HexRendering) is no different than a default rendering. So why
does it exist?
* Can one provide non-textual renderings? For example, render bytes as an
image? (I didn't get to the UI code yet, but I presume this is possible)
* What types of rendering properties are used/supported? What are dynamic
renderings? So far, I can see only this explicit use of properties, but
it?s not clear to me what a dynamic rendering is.

I did not change any code yet, but I modifed the memoryRenderings schema
to reflect my understanding of things:
* I modified the wording in the memoryRenderings schema to note that the
extension point becomes public in 3.1, and added references to the memory
block type identifier. Deprecated the memoryBlockClass attribute of the
default renderings and rendering binding elements. Removed renderingId
from the renderingProperty element.

Other review notes:
* As a matter of style/consistency with other extension points, the names
of elements in the memoryRenderings extension point should be changed from
"rendering_property" to "renderingProperty", etc.
* An example extension should be included in the schema (in an Example
section), and API information should be provided in the API section - i.e.
describing the API references from the example.
* The "Supplied Implementation" section should describe what the debug
platform provides - i.e. a HEX rendering.
* I have other review notes for the code (i.e. written on printouts), not
included here


Thanks,

Darin
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