System.Threading.Tasks.Parallel.Tests fails on Android

[mdh1418]

One test from System.Threading.Tasks.Parallel.Tests fails on Android

• System.Threading.Tasks.Tests.ParallelForEachAsyncTests.Dop_WorkersCreatedRespectingLimitAndTaskScheduler_Sync(dop: -1)

System.Threading.Tasks.Parallel.Tests.dll   Failed: 1

Test collection for System.Threading.Tasks.Parallel.Tests.dll
System.Threading.Tasks.Tests.ParallelForEachAsyncTests.Dop_WorkersCreatedRespectingLimitAndTaskScheduler_Sync(dop: -1)
    Assert.InRange() Failure\r\nRange:  (0 - 1)\r\nActual: 2

Based on CI runs from #50095

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Issue Details

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One test from System.Threading.Tasks.Parallel.Tests fails on Android

• System.Threading.Tasks.Tests.ParallelForEachAsyncTests.Dop_WorkersCreatedRespectingLimitAndTaskScheduler_Sync(dop: -1)

Based on CI runs from #50095

Author:	mdh1418
Assignees:	-
Labels:	area-System.Threading.Tasks, os-android
Milestone:	6.0.0

[mdh1418]

It looks like

If it is -1, there is no limit on the number of concurrently running operations (with the exception of the ForEachAsync method, where -1 means ProcessorCount.

from https://docs.microsoft.com/en-us/dotnet/api/system.threading.tasks.paralleloptions.maxdegreeofparallelism?view=net-6.0#system-threading-tasks-paralleloptions-maxdegreeofparallelism is not being honored, as in the ProcessorCount is 1, but the Parallel.ForEachAsync is using 2 schedulers.

[mdh1418]

Looking through the code path, it seems like the test with MaxDegreeOfParallelism = -1 (unlimited) with MaxSchedulerLimit = 2 passed through Parallel.ForEachAsync will end up having EffectiveMaxConcurrencyLevel = 2

runtime/src/libraries/System.Threading.Tasks.Parallel/src/System/Threading/Tasks/Parallel.cs

Lines 107 to 120 in 63b2656

	internal int EffectiveMaxConcurrencyLevel
	{
	get
	{
	int rval = MaxDegreeOfParallelism;
	int schedulerMax = EffectiveTaskScheduler.MaximumConcurrencyLevel;
	if ((schedulerMax > 0) && (schedulerMax != int.MaxValue))
	{
	rval = (rval == -1) ? schedulerMax : Math.Min(schedulerMax, rval);
	}
	return rval;
	}
	}
	} // class ParallelOptions

and does not hit this code path

runtime/src/libraries/System.Threading.Tasks.Parallel/src/System/Threading/Tasks/Parallel.ForEachAsync.cs

Lines 79 to 82 in 63b2656

	if (dop < 0)
	{
	dop = DefaultDegreeOfParallelism;
	}

which should have set it to the expected Environment.ProcessorCount

runtime/src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Scheduling/Scheduling.cs

Line 35 in 57bfe47

internal static int DefaultDegreeOfParallelism = Math.Min(Environment.ProcessorCount, MAX_SUPPORTED_DOP);

But I'm not sure why this fails only on Android. Is its Environment.ProcessorCount not supposed to be 1?