On 10/29/10 15:18, Jim Deville wrote:
C# 4.0 has WeakMap's too, and one of the goals was to work around the cyclical
reference issue:
http://blogs.msdn.com/b/clrteam/archive/2009/05/18/the-conditional-weak-table-enabling-dynamic-object-properties.aspx
mono implements ConditionalWeakTable with Ephemeron tables registered
with the GC. The registration does nothing with boehm-gc, but there is
special handling for Ephemerons in the experimental sgen-gc, and it
looks to me like it's similar to what's described on the ECMAScript wiki
for WeakMap: repeatedly scan Ephemeron key,value entries for values that
are newly reachable, until no more newly-reachable values are found.
http://github.com/mono/mono/blob/09ae7f243df64f6928ffcd89eb44ac1f688c689e/mono/metadata/sgen-gc.c
it's instrumented to count how many times it repeats the Ephemeron scan,
so it probably wouldn't be too hard to get practical data on how
expensive it is in real usage.
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