Bug 58399 - Delegates as collection key are ~500x slower than previously
Summary: Delegates as collection key are ~500x slower than previously
Alias: None
Product: Class Libraries
Classification: Mono
Component: mscorlib ()
Version: unspecified
Hardware: PC Windows
: --- normal
Target Milestone: Untriaged
Assignee: Bugzilla
Depends on:
Reported: 2017-07-25 20:18 UTC by Jonathan Chambers
Modified: 2017-08-02 07:03 UTC (History)
4 users (show)

Is this bug a regression?: ---
Last known good build:

Test Case (1.16 KB, text/plain)
2017-07-25 20:18 UTC, Jonathan Chambers

Notice (2018-05-24): bugzilla.xamarin.com is now in read-only mode.

Please join us on Visual Studio Developer Community and in the Xamarin and Mono organizations on GitHub to continue tracking issues. Bugzilla will remain available for reference in read-only mode. We will continue to work on open Bugzilla bugs, copy them to the new locations as needed for follow-up, and add the new items under Related Links.

Our sincere thanks to everyone who has contributed on this bug tracker over the years. Thanks also for your understanding as we make these adjustments and improvements for the future.

Please create a new report on GitHub or Developer Community with your current version information, steps to reproduce, and relevant error messages or log files if you are hitting an issue that looks similar to this resolved bug and you do not yet see a matching new report.

Related Links:

Description Jonathan Chambers 2017-07-25 20:18:47 UTC
Created attachment 23798 [details]
Test Case

Run attached test case:

MS: 800ms
Mono 5.0: 500ms
Mono 2.6: 1ms
Comment 1 Zoltan Varga 2017-07-25 20:33:39 UTC
This happens because delegates have the same hash code as their delegate type:

		public override int GetHashCode ()
			/* same implementation as CoreCLR */
			return GetType ().GetHashCode ();

So all the delegates end up in the same hash bucket. A workaround is to use a custom comparer which can provide its own hashcode.
Comment 2 Zoltan Varga 2017-08-01 14:00:00 UTC
Comment 3 Zoltan Varga 2017-08-02 07:03:29 UTC
Fixed in mono master a48bc439850869e565833d7fe6330c289beffe40.