I've got an application that needs to draw a graph, so I'm using Cairo
to render it. This works really well. But I didn't realize until
recently that code like this was problematic:
(html image)
document: ws contents
mimeType: 'image/png'
.. since it created WADocumentHandler instances that are never
collected. I don't want these graphs to live forever in the image --
they don't even need to be cached on the server, and they ought to be
specific to a particular session. It's a similar situation to when I'm
generating a CSV export of a client's data: the document is a one-time
throw-away.
It seems like a callback is the right way to solve this (it's what I
used in the CSV case too), so I hacked it together like so:
renderGraphOn: html
(html image)
class: 'graph';
url: (html context actionUrl copy addParameter:
(html callbacks registerCallback:
[self session respond:
[:url |
| ws |
ws := ByteArray new writeStream.
self writePngOn: ws.
Seaside.WAResponse document: ws contents mimeType: 'image/
png']]))
This has the desired effect of linking the graph to the current
session, and so far is appears to be free of the memory leak I was
creating earlier using WADocumentHandler. Is this the right approach,
or is there a better way? And if it's the right approach, can we add
something like a #documentCallback: method to WAImageTag to make it
easier to code things like this?
renderGraphOn: html
(html image)
class: 'graph';
documentCallback:
[| ws |
ws := ByteArray new writeStream.
self writePngOn: ws.
Seaside.WAResponse document: ws contents mimeType: 'image/png']
--
Ken Treis
Miriam Technologies, Inc.
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