{"action":"opened","number":5518,"pull_request":{"url":"https://api.github.com/repos/dotnet/corefx/pulls/5518","id":56493097,"html_url":"https://github.com/dotnet/corefx/pull/5518","diff_url":"https://github.com/dotnet/corefx/pull/5518.diff","patch_url":"https://github.com/dotnet/corefx/pull/5518.patch","issue_url":"https://api.github.com/repos/dotnet/corefx/issues/5518","number":5518,"state":"open","locked":false,"title":"Tweak ConcurrentDictionary perf","user":{"login":"stephentoub","id":2642209,"avatar_url":"https://avatars.githubusercontent.com/u/2642209?v=3","gravatar_id":"","url":"https://api.github.com/users/stephentoub","html_url":"https://github.com/stephentoub","followers_url":"https://api.github.com/users/stephentoub/followers","following_url":"https://api.github.com/users/stephentoub/following{/other_user}","gists_url":"https://api.github.com/users/stephentoub/gists{/gist_id}","starred_url":"https://api.github.com/users/stephentoub/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/stephentoub/subscriptions","organizations_url":"https://api.github.com/users/stephentoub/orgs","repos_url":"https://api.github.com/users/stephentoub/repos","events_url":"https://api.github.com/users/stephentoub/events{/privacy}","received_events_url":"https://api.github.com/users/stephentoub/received_events","type":"User","site_admin":false},"body":"- Decrease memory consumption when using default ctor.  Today by default ConcurrentDictionary assumes a default concurrencyLevel of Environment.ProcessCount * 4.  That multiple results in only marginal throughput improvements even on extremely write-heavy workloads, but it results in significant additional memory consumption for small-to-medium sized dictionaries, due to allocating the various objects used for striped locking.  I've changed the default to lose the multiple and just be Environment.ProcessorCount.  I was unable to find a workload that produced a meaningful regression (in fact some seemed to get a bit faster).  I was able to find regressions if I used a default lower than that, e.g. defaulting 1... developers can always choose to explicitly specify a concurrencyLevel of 1 via the ctor, in which case memory consumption will be lowered and all writes will be serialized on that one lock (reads are always lock-free, regardless of concurrency level).  We can of course consider changing the default down to 1 in the future.\r\n\r\n- Made several read operations more inlineable.  Methods like TryGetValue weren't being inlined due to the JIT's size estimate saying it'd be too big.  By factoring out the throw expressions into non-inlineable methods, the JIT now inlines them.  In various microbenchmarks, this improved TryGetValue, ContainsKey, etc. throughput upwards of ~20%.\r\n\r\n- Made a few types sealed and a few members readonly.\r\n\r\n- Fixed up several style issues.\r\n\r\ncc: @vancem, @AlfredoMS 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