override intellisense is extremely slow

[cwensley]

Issue Description

When getting intellisense for methods/properties to override in a class, it can be extremely slow for large projects, and really kills productivity.

Intellisense when typing base. is extremely fast, so it makes me think it can go a lot faster in this case.

Steps to Reproduce

1. In a class, type "override " and start typing a method or property to override

Expected Behavior

It should come up quickly.

Actual Behavior

It takes forever for my project in a large solution. Even pressing ctrl+space to force it to show intellisense takes a long time:

Logs

OmniSharp log

Received response for /v2/blockstructure but could not find request. Received response for /v2/blockstructure but could not find request. Received response for /v2/getcodeactions but could not find request. Received response for /completion but could not find request.

C# log

(it's blank)

Environment information

VSCode version: 1.56.2
C# Extension: 1.23.11

Mono Information

OmniSharp using global mono :6.12.0

Dotnet Information

.NET SDK (reflecting any global.json): Version: 6.0.100-preview.3.21202.5 Commit: aee38a6dd4

Runtime Environment:
OS Name: Mac OS X
OS Version: 11.0
OS Platform: Darwin
RID: osx.11.0-x64
Base Path: /usr/local/share/dotnet/sdk/6.0.100-preview.3.21202.5/

Host (useful for support):
Version: 6.0.0-preview.3.21201.4
Commit: 236cb21e3c

.NET SDKs installed:
2.1.500 [/usr/local/share/dotnet/sdk]
2.1.811 [/usr/local/share/dotnet/sdk]
3.1.100 [/usr/local/share/dotnet/sdk]
3.1.101 [/usr/local/share/dotnet/sdk]
3.1.102 [/usr/local/share/dotnet/sdk]
3.1.200 [/usr/local/share/dotnet/sdk]
3.1.300 [/usr/local/share/dotnet/sdk]
3.1.301 [/usr/local/share/dotnet/sdk]
3.1.302 [/usr/local/share/dotnet/sdk]
3.1.402 [/usr/local/share/dotnet/sdk]
3.1.403 [/usr/local/share/dotnet/sdk]
3.1.404 [/usr/local/share/dotnet/sdk]
3.1.406 [/usr/local/share/dotnet/sdk]
3.1.407 [/usr/local/share/dotnet/sdk]
3.1.409 [/usr/local/share/dotnet/sdk]
5.0.100 [/usr/local/share/dotnet/sdk]
5.0.102 [/usr/local/share/dotnet/sdk]
5.0.103 [/usr/local/share/dotnet/sdk]
5.0.201 [/usr/local/share/dotnet/sdk]
5.0.203 [/usr/local/share/dotnet/sdk]
6.0.100-alpha.1.21057.10 [/usr/local/share/dotnet/sdk]
6.0.100-alpha.1.21062.4 [/usr/local/share/dotnet/sdk]
6.0.100-preview.1.21103.13 [/usr/local/share/dotnet/sdk]
6.0.100-preview.2.21155.3 [/usr/local/share/dotnet/sdk]
6.0.100-preview.3.21202.5 [/usr/local/share/dotnet/sdk]

.NET runtimes installed:
Microsoft.AspNetCore.All 2.1.6 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.22 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.23 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.6 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.23 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.1 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.2 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.4 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.5 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.6 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.8 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.9 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.10 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.12 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.13 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.15 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.2 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.3 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.4 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.6 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.0-alpha.1.21057.7 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.0-alpha.1.21061.6 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.0-preview.1.21103.6 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.0-preview.2.21154.6 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.0-preview.3.21201.13 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.6 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.23 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.1 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.2 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.4 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.6 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.8 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.9 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.10 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.12 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.13 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.15 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.2 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.3 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.4 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.6 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.0-alpha.1.21057.2 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.0-alpha.1.21061.20 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.0-preview.3.21201.4 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET runtimes or SDKs:
https://aka.ms/dotnet-download

Visual Studio Code Extensions

Extension	Author	Version
cpptools	ms-vscode	1.3.1
csharp	ms-dotnettools	1.23.11
csharpextensions	jchannon	1.3.1
docomment	k--kato	0.1.20
dotenv	mikestead	1.0.1
dotnet	leo-labs	1.3.0
dotnet-test-explorer	formulahendry	0.7.5
EditorConfig	EditorConfig	0.16.4
ilspy-vscode	icsharpcode	0.10.0
luna-paint	Tyriar	0.5.1
lunatic-file-picker	DmitriyMuraviov	0.1.2
macros	geddski	1.2.1
mono-debug	ms-vscode	0.16.2
msbuild-project-tools	tintoy	0.3.15
rhino-debug	mcneel	0.4.0
rtf	alefragnani	2.2.0
shader	slevesque	1.1.5
syntax-project-pbxproj	mariomatheu	0.1.3
uuid-generator	netcorext	0.0.4
vscode-clangd	llvm-vs-code-extensions	0.1.11
vscode-eslint	dbaeumer	2.1.20
vscode-nuget-package-manager	jmrog	1.1.6
vscode-open-in-github	fabiospampinato	1.3.0
vscode-pull-request-github	GitHub	0.26.0
vscode-pylance	ms-python	2021.5.2
vscode-solution-explorer	fernandoescolar	0.4.3
vscode-yaml	redhat	0.19.0
xml	DotJoshJohnson	2.5.1

[333fred]

See the discussion in #4116. The next version of OmniSharp will have an experimental async mode, but keep in mind that the completion we're doing there is a race condition waiting to happen and you may experience unexpected results. Until we get a proper async completion api, there's not much we can do.