Optimize and simplify delegate layout by MichalPetryka · Pull Request #99200 · dotnet/runtime

MichalPetryka · 2024-03-03T01:50:15Z

First attempt at making delegate GC fields immutable in CoreCLR so that they can be allocated on the NonGC heap.

I've checked it with a simple app and corerun locally with a delegate from an unloadable ALC and it seemed to not crash, assert nor unload the ALC from under the delegate, however I couldn't actually find any runtime tests that would verify delegates from unloadable ALCs work so the CI coverage might be missing.

One small point of concern is that this might make delegate equality checks slower since they rely on checking the methods in the last "slow path" check, which is however always hit for different delegates AFAIR.

Contributes to #85014.

cc @jkotas

MichalPetryka · 2024-03-04T00:01:32Z

I'm not sure what's up with the failures here, tests that are failing on the CI seem to pass on my machine.
EDIT: I was testing with R2R disabled locally since VS kept complaining about being unable to load PDBs for it.

Co-authored-by: Jan Kotas <jkotas@microsoft.com>

AndyAyersMS · 2024-03-05T22:15:03Z

/azp run runtime-coreclr gcstress0x3-gcstress0xc

azure-pipelines · 2024-03-05T22:15:18Z

Azure Pipelines successfully started running 1 pipeline(s).

jkotas · 2024-03-05T22:33:41Z

Could you please collect some perf numbers to give us an idea about the improvements and regressions in the affected areas? We may want to do some optimizations to mitigate the regressions.

jkotas · 2024-03-05T22:48:32Z

One small point of concern is that this might make delegate equality checks slower since they rely on checking the methods in the last "slow path" check, which is however always hit for different delegates AFAIR.

The existing code tries to compare MethodInfos as a cheap fast path. Most delegates do not have cached MethodInfo, so this fast path is hit rarely - but it is very cheap, so it is still worth it.

This cheap fast path is not cheap anymore with this change. It may be best to delete the fast path that is trying to compare the MethodInfos and potentially optimize Delegate_InternalEqualMethodHandles instead.

MichalPetryka · 2024-03-05T22:52:56Z

Could you please collect some perf numbers to give us an idea about the improvements and regressions in the affected areas? We may want to do some optimizations to mitigate the regressions.

I think the thing that'd need benchmarking here are equality checks and maybe the impact of collectible delegates being stored in the CWT on the GC, the rest of things shouldn't be performance sensitive enough to matter I think? I'm not fully sure what'd be the proper way for benchmarking the latter.

This cheap fast path is not cheap anymore with this change. It may be best to delete the fast path that is trying to compare the MethodInfos and potentially optimize Delegate_InternalEqualMethodHandles instead.

I am going to benchmark the impact of the equality change tomorrow, I feel like if the impact won't be big, potential optimizations to it can be done later.

jkotas · 2024-03-05T23:02:52Z

I'm not fully sure what'd be the proper way for benchmarking the latter.

Write a small program that loads an assembly as collectible and calls a method in it. The method in collectible assembly can create delegates in a loop. (If you would like to do it under benchmarknet, it works too - but it is probably more work.)

Co-authored-by: Jan Kotas <jkotas@microsoft.com>

Moved UnmanagedMarker constant declaration to the top of the struct.

Simplified GetMethodDesc by removing unnecessary variable and conditional.

jkotas · 2026-07-11T04:21:54Z

-    static MethodDesc* GetMethodDescForOpenVirtualDelegate(OBJECTREF orDelegate);
-    static BOOL IsTrueMulticastDelegate(OBJECTREF delegate);
+    static MethodDesc* GetMethodDesc(OBJECTREF obj);
+    static MethodDesc* GetCachedMethodDesc(DELEGATEREF delegate);


Suggested change

static MethodDesc* GetCachedMethodDesc(DELEGATEREF delegate);

static MethodDesc* GetMethodDescForOpenVirtualDelegate(DELEGATEREF delegate);

If you apply my other feedback, this can stay with the more specific name

I don't think the old name makes sense anymore since it will return results for non open virtual delegates.

The implementation can assert that it is only used for open virtual delegates.

The implementation can assert that it is only used for open virtual delegates.

I don't think there's an easy way to do that anymore? We'd need to check if the method is virtual and that the delegate is open which need a lot of checks.

Right, we would have to assert that the aux pointer points into VSD heap. I am not sure how hard is it to put the assert together. Asserting is optional to enforce the precondition. We have many methods in the VM that document the preconditions without asserting them.

It is better to name cross-component calls based on their external contract, not based on the implementation details. It makes the code easier to understand, and it makes refactoring easier. For example, GetMethodDescForOpenVirtualDelegate name is likely to survive changes in implementation details. GetCachedMethodDesc name not so much.

Co-authored-by: Jan Kotas <jkotas@microsoft.com>

jkotas · 2026-07-11T04:58:12Z

/__w/1/s/src/coreclr/System.Private.CoreLib/src/System/Delegate.CoreCLR.cs(336,25): error CS0128: A local variable or function named 'method' is already defined in this scope [/__w/1/s/src/coreclr/System.Private.CoreLib/System.Private.CoreLib.csproj]
/__w/1/s/src/coreclr/System.Private.CoreLib/src/System/Delegate.CoreCLR.cs(340,20): error CS0266: Cannot implicitly convert type 'System.IRuntimeMethodInfo' to 'System.Reflection.MethodInfo'. An explicit conversion exists (are you missing a cast?) [/__w/1/s/src/coreclr/System.Private.CoreLib/System.Private.CoreLib.csproj]
/__w/1/s/src/coreclr/System.Private.CoreLib/src/System/Delegate.CoreCLR.cs(336,25): error IDE0059: Unnecessary assignment of a value to 'method' (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0059) [/__w/1/s/src/coreclr/System.Private.CoreLib/System.Private.CoreLib.csproj]

Copilot

Pull request overview

Copilot reviewed 22 out of 22 changed files in this pull request and generated 3 comments.

Comments suppressed due to low confidence (1)

src/native/managed/cdac/tests/UnitTests/ObjectTests.cs:450

GetDelegateInfo now has explicit multicast detection via Delegate.HelperObject being an array, but the unit tests no longer exercise that path (the previous "Multicast" test was repurposed to "Unmanaged"). Please add a multicast test that sets HelperObject to an array object and verifies DelegateType.Unknown (and zeroed Target/MethodPtr) for multicast delegates.

    [Theory]
    [ClassData(typeof(MockTarget.StdArch))]
    public void GetDelegateInfo_Unmanaged(MockTarget.Architecture arch)
    {
        const ulong TestMethodTable = 0x00000000_10000200;
        const ulong TestMethodPtr = 0x00000000_aaaa0000;
        const long TestExtraData = -1;
        TargetPointer delegateAddress = default;

        IObject contract = CreateObjectContract(
            arch,
            objectBuilder =>
            {
                delegateAddress = objectBuilder.AddDelegateObject(
                    methodTable: TestMethodTable,
                    target: 0,
                    methodPtr: TestMethodPtr,
                    methodPtrAux: 0,
                    extraData: TestExtraData);
            });

        DelegateInfo info = contract.GetDelegateInfo(delegateAddress);

        Assert.Equal(DelegateType.Unknown, info.DelegateType);
        Assert.Equal(0ul, info.TargetObject.Value);
        Assert.Equal(0ul, info.TargetMethodPtr.Value);
    }

MichalPetryka · 2026-07-11T05:37:25Z

+                // both delegates are open
+                if (_methodPtrAux == other._methodPtrAux)
+                    return true;


@jkotas was this a preexisting bug?

Yes, it looks like it.

I think it is only a problem for FEATURE_CACHED_INTERFACE_DISPATCH that is only used in production on iOS.

We should add a test that hits the issue before fixing it.

        // A null invocationList can be one of the following:
-        //  - Instance closed, Instance open non-virt, Instance open virtual, Static closed, Static opened, Unmanaged FtnPtr
-        //  - Instance open virtual is complex and we need to figure out what to do (TODO).
-        // For the others the logic is the following:
-        // if _methodPtrAux is 0 the target is in _methodPtr, otherwise the taret is _methodPtrAux
+        // - Instance closed
+        // - Instance open non-virt
+        // - Instance open virtual
+        // - Static closed
+        // - Static opened
+        // - Instance open virtual
+        // - Unmanaged FtnPtr
+        // if _methodPtrAux is 0 the target is in _methodPtr, otherwise the target is _methodPtrAux


+Contract Constants:
+| Name | Type | Purpose | Value |
+| --- | --- | --- | --- |
+| `UnmanagedMarker` | nint | Sentinel value for detecting unmanaged pointer delegates. | `-1` |
+


jkotas · 2026-07-11T06:13:58Z

+
+            MethodTable* methodTable = RuntimeHelpers.GetMethodTable(this);
+#if FEATURE_TYPEEQUIVALENCE
+            if (methodTable->HasTypeEquivalence)


I have started PR to add a test that hits this path: #130542 . The test should fail against main now, and it should pass once this PR is merged.

jkotas · 2026-07-12T05:30:32Z

LGTM once the remaining feedback is addressed

MichalPetryka · 2026-07-13T01:00:30Z

LGTM once the remaining feedback is addressed

I'll get to it tomorrow

Make delegates immutable

5b3126e

ghost added the area-VM-coreclr label Mar 3, 2024

MichalPetryka and others added 3 commits March 3, 2024 02:53

Add a comment

64baa1d

Optimize cache checks

a489288

Merge branch 'main' into immutable-delegates

b0b31bd

build-analysis Bot mentioned this pull request Mar 3, 2024

LibraryImportGenerator unit test segfault illegal memory access #89054

Closed

Fix x86

bc132e4

Fix R2R

2dce6a8

runfoapp Bot mentioned this pull request Mar 4, 2024

Methodical_others test JIT/Methodical/Coverage/copy_prop_byref_to_native_int crashing #69832

Open

MichalPetryka added 2 commits March 4, 2024 16:30

Update methodcontext.cpp

00fcd02

Fix contract

7941123

jkotas reviewed Mar 4, 2024

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Comment thread src/coreclr/vm/object.cpp Outdated

jkotas reviewed Mar 4, 2024

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Comment thread src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs Outdated

MichalPetryka and others added 3 commits March 4, 2024 16:40

Update src/coreclr/vm/object.cpp

4de2754

Co-authored-by: Jan Kotas <jkotas@microsoft.com>

Swap fields

b9f7f14

Reorder asserts

90c6085

MichalPetryka mentioned this pull request Mar 4, 2024

When min major R2R version moves forward, consider some cleanups #98871

Closed

MichalPetryka added 2 commits March 4, 2024 19:12

Fix contract again

9509023

GCPROTECT

557bf4d

MichalPetryka marked this pull request as ready for review March 4, 2024 23:28

build-analysis Bot mentioned this pull request Mar 5, 2024

Tracking issue for CI build timeouts #76454

Closed

MichalPetryka added 2 commits March 5, 2024 21:12

Merge branch 'main' into immutable-delegates

1eab602

Merge branch 'main' into immutable-delegates

477a3c5

rcj1 reviewed Jul 11, 2026

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Comment thread src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/Delegate.cs Outdated

MichalPetryka added 2 commits July 11, 2026 05:27

Update Delegate.cs

28de884

Replace Data.Delegate.UnmanagedMarker with constant

9982821

jkotas reviewed Jul 11, 2026

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Comment thread src/coreclr/System.Private.CoreLib/src/System/Delegate.CoreCLR.cs Outdated

jkotas reviewed Jul 11, 2026

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Comment thread src/coreclr/System.Private.CoreLib/src/System/Delegate.CoreCLR.cs

MichalPetryka and others added 2 commits July 11, 2026 05:53

Update src/coreclr/System.Private.CoreLib/src/System/Delegate.CoreCLR.cs

d771cf4

Co-authored-by: Jan Kotas <jkotas@microsoft.com>

Seal Equals and GetHashCode methods in Delegate class

30bdb4c

rcj1 reviewed Jul 11, 2026

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Comment thread ...native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/Object_1.cs Outdated

jkotas reviewed Jul 11, 2026

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Comment thread src/coreclr/vm/comdelegate.cpp Outdated

Refactor UnmanagedMarker declaration position

7994cb8

Moved UnmanagedMarker constant declaration to the top of the struct.

jkotas reviewed Jul 11, 2026

View reviewed changes

Comment thread src/coreclr/System.Private.CoreLib/src/System/Delegate.CoreCLR.cs Outdated

MichalPetryka added 2 commits July 11, 2026 06:15

Rename variable fRet to pMD in Delegate_GetMethodDesc

d2c2fed

Refactor GetMethodDesc for clarity

9448351

Simplified GetMethodDesc by removing unnecessary variable and conditional.

jkotas reviewed Jul 11, 2026

View reviewed changes

Comment thread src/coreclr/vm/comdelegate.cpp Outdated

jkotas reviewed Jul 11, 2026

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Update src/coreclr/vm/comdelegate.cpp

4914734

Co-authored-by: Jan Kotas <jkotas@microsoft.com>

jkotas reviewed Jul 11, 2026

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Comment thread ...native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/Object_1.cs

build-analysis Bot mentioned this pull request Jul 11, 2026

Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. dotnet/dnceng#5922

Open

3 tasks

Rename variable for clarity in Delegate.CoreCLR.cs

8db2814

jkotas requested a review from Copilot July 11, 2026 05:24

Copilot started reviewing on behalf of jkotas July 11, 2026 05:25 View session

Copilot AI reviewed Jul 11, 2026

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jkotas reviewed Jul 11, 2026

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This was referenced Jul 12, 2026

Unable to pull image from mcr.microsoft.com #117164

Open

[ci-scan] Test failure: browser-wasm CoreCLR tests abort at startup with WebAssembly exnref CompileError (invalid value type 'ex [Content truncated due to length] #130571

Open

jkotas mentioned this pull request Jul 13, 2026

Fix Delegate.GetHashCode for type-equivalent delegates #130542

Open

Copilot AI mentioned this pull request Jul 13, 2026

[WIP] Revert last commit to address feedback on Delegate.GetHashCode fix PR #130597

Merged

	static MethodDesc* GetCachedMethodDesc(DELEGATEREF delegate);
	static MethodDesc* GetMethodDescForOpenVirtualDelegate(DELEGATEREF delegate);

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