[RuntimeAsync] Removing TODO in methodtablebuilder.cpp. More robust insertion of methods. #122377

VSadov · 2025-12-10T03:34:21Z

To make the insertion of methods more robust we:

double the capacity of the MT builder up to the absolute limit required by the implementation of MethodDesc.
check if we still fit in the budget when adding methods.

Note: it may result in some programs that used to run to start throwing TypeLoadException.

These would be extreme cases though. The capacity for simple methods is implementation-specific. In CoreCLR a type cannot contain more than 65524 methods due to internal limitations.
(More complex cases involving inheritance/virtual methods may have additional limits.)

With runtime async, methods that return Task/ValueTask may consume 2 methods instead of 1 from this 65524 budget.
In a worst case where all methods return Task, the limit becomes 32762 methods in a single type, which still seems a very high limit for reasonably real programs that are not generated testcases.

dotnet-policy-service · 2025-12-10T03:35:48Z

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VSadov · 2025-12-10T03:35:55Z

src/coreclr/inc/clrconfigvalues.h


 // Runtime-async
-RETAIL_CONFIG_DWORD_INFO(UNSUPPORTED_RuntimeAsync, W("RuntimeAsync"), 0, "Enables runtime async method support")
+RETAIL_CONFIG_DWORD_INFO(UNSUPPORTED_RuntimeAsync, W("RuntimeAsync"), 1, "Enables runtime async method support")


TODO: undo the commit that enables async

jkotas · 2025-12-10T17:51:17Z

src/coreclr/vm/methodtablebuilder.cpp

-    bmtMethod->m_cMaxDeclaredMethods = (SLOT_INDEX)cMethAndGaps;
-
+    DWORD cMethUpperBound = cMethAndGaps;
    if (g_pConfig->RuntimeAsync())


Should this if-check be deleted?

I guess so. The new behavior does not need to be conditional.

Co-authored-by: VSadov <[email protected]>

@VSadov

Per @VSadov's feedback, replaced runtime type generation with actual source-defined classes containing 40k and 32k+ methods. Co-authored-by: VSadov <[email protected]>

VSadov · 2025-12-11T00:44:06Z

src/coreclr/utilcode/allocmemtracker.cpp

    for (int i = 0; pDebugBlock != &m_FirstBlock; i++)
    {
-        CONSISTENCY_CHECK_MSGF(i < 10000, ("Linked list is much longer than expected, memory corruption likely\n"));
+        CONSISTENCY_CHECK_MSGF(i < 60000, ("Linked list is much longer than expected, memory corruption likely\n"));


The new capacity test was hitting this assert. I think the assert checks for loops in the list.

Copilot

Pull request overview

This PR removes a TODO comment in methodtablebuilder.cpp and makes the insertion of async method variants more robust by implementing proper capacity management and bounds checking. The changes enable RuntimeAsync by default and add comprehensive tests to verify the new method capacity limits.

Implements robust capacity doubling for async methods (up to MAX_SLOT_INDEX - 1 = 65524)
Adds runtime bounds checking before method insertion to prevent array overflow
Enables RuntimeAsync by default for CoreCLR and enables corresponding tests

Reviewed changes

Copilot reviewed 6 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/coreclr/vm/methodtablebuilder.cpp	Replaces conditional capacity doubling with robust upfront capacity calculation clamped to MAX_SLOT_INDEX - 1, and adds bounds check before method insertion to throw TypeLoadException when limit is exceeded
src/coreclr/utilcode/allocmemtracker.cpp	Increases consistency check threshold from 10,000 to 60,000 blocks to accommodate larger classes with up to 65,524 methods
src/coreclr/inc/clrconfigvalues.h	Enables RuntimeAsync feature by default (changes default value from 0 to 1)
src/tests/async/Directory.Build.targets	Removes the DisableProjectBuild condition to enable async tests for CoreCLR (non-nativeaot) builds
src/tests/async/capacity/capacity.csproj	Defines new test project structure including test file and three generated test class files
src/tests/async/capacity/capacity.cs	Adds three test scenarios: 40,000 int-returning methods (should succeed), 32,750 Task-returning methods (should succeed), and 32,763 Task-returning methods (should fail with TypeLoadException)

jkotas · 2025-12-11T04:17:31Z

src/coreclr/vm/methodtablebuilder.cpp

+    // The method count is typically a modest number though.
+    // We will reserve twice the size for the builder, up to the max, just in case.
+    DWORD cMethUpperBound = cMethAndGaps * 2;
+    if (cMethUpperBound >= (DWORD)MAX_SLOT_INDEX)


Suggested change

if (cMethUpperBound >= (DWORD)MAX_SLOT_INDEX)

if ((DWORD)MAX_SLOT_INDEX <= cMethUpperBound)

So that it is same style as if ((DWORD)MAX_SLOT_INDEX <= cMethAndGaps) a few lines above

jkotas · 2025-12-11T04:19:57Z

src/tests/async/capacity/capacity.cs

+    }
+
+    [Fact]
+    public static void TestLargeClassWithTaskMethods_Exception()


This test is testing CoreCLR specific implementation limitation. Is it going to pass on Native AOT? If not, it should be disabled there.

And if it is testing CoreCLR specific implementation limitation, we may consider using Reflection.Emit to generate the test types on the fly to avoid these very large source files being checked in.

jkotas

LGTM otherwise. Thanks!

VSadov added the runtime-async label Dec 10, 2025

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VSadov added area-VM-coreclr and removed needs-area-label An area label is needed to ensure this gets routed to the appropriate area owners labels Dec 10, 2025

VSadov added this to the 11.0.0 milestone Dec 10, 2025

VSadov commented Dec 10, 2025

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jkotas reviewed Dec 10, 2025

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VSadov and others added 8 commits December 10, 2025 15:21

Enable async feature/tests

6975252

Check method table builder capacity before adding declared methods.

273a919

Use larger builder capacity unconditionally.

85c9cd6

Initial plan

dd00370

Add capacity test for type system limits with large number of methods

637d3eb

Co-authored-by: VSadov <[email protected]>

Fix null-check warnings in capacity test

a1e5c14

Co-authored-by: VSadov <[email protected]>

Use real classes instead of Reflection.Emit for capacity tests

25b3e54

Per @VSadov's feedback, replaced runtime type generation with actual source-defined classes containing 40k and 32k+ methods. Co-authored-by: VSadov <[email protected]>

Adjust capacity testcases.

65709eb

VSadov force-pushed the TODOmt branch from 0b2a488 to 65709eb Compare December 10, 2025 23:21

VSadov mentioned this pull request Dec 10, 2025

Add capacity test for type system limits with large method counts #122412

Closed

relax an assert in alloc tracker

79eb1fd

VSadov marked this pull request as ready for review December 11, 2025 00:42

VSadov requested review from Copilot and jkotas December 11, 2025 00:42

Copilot started reviewing on behalf of VSadov December 11, 2025 00:43 View session

VSadov commented Dec 11, 2025

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Copilot AI reviewed Dec 11, 2025

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jkotas reviewed Dec 11, 2025

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jkotas approved these changes Dec 11, 2025

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build-analysis bot mentioned this pull request Dec 11, 2025

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[RuntimeAsync] Removing TODO in methodtablebuilder.cpp. More robust insertion of methods. #122377

[RuntimeAsync] Removing TODO in methodtablebuilder.cpp. More robust insertion of methods. #122377

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	if (cMethUpperBound >= (DWORD)MAX_SLOT_INDEX)
	if ((DWORD)MAX_SLOT_INDEX <= cMethUpperBound)

[RuntimeAsync] Removing TODO in methodtablebuilder.cpp. More robust insertion of methods. #122377

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[RuntimeAsync] Removing TODO in methodtablebuilder.cpp. More robust insertion of methods. #122377

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VSadov commented Dec 10, 2025 •

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