Fix a thread pool test

- The test verifies that cooperative blocking in `Task.Wait()` causes threads to be injected quickly enough that it does not time out due to starvation
- Cooperative blocking checks memory usage and limit, and beyond a threshold of memory usage does not inject threads quickly
- Following a build of the runtime repo, there are several `dotnet` processes that remain running, each using several 100s of MBs and one using ~1.3 GB of memory
- If the test runs soon after the build, before those processes exit, it's possible for the reported memory usage to be high enough that the test would fail
- Added a config var to ignore memory usage and used it in the test

Fixes dotnet#66852

src/libraries/System.Private.CoreLib/src/System/Threading/PortableThreadPool.Blocking.cs

@@ -180,7 +180,7 @@ private uint PerformBlockingAdjustment(bool previousDelayElapsed, out bool addWo
 
                 do
                 {
-                    if (newNumThreadsGoal <= counts.NumExistingThreads)
+                    if (newNumThreadsGoal <= counts.NumExistingThreads || BlockingConfig.IgnoreMemoryUsage)
                     {
                         break;
                     }
@@ -260,6 +260,8 @@ private static class BlockingConfig
         {
             public static readonly bool IsCooperativeBlockingEnabled =
                 AppContextConfigHelper.GetBooleanConfig("System.Threading.ThreadPool.Blocking.CooperativeBlocking", true);
+            public static readonly bool IgnoreMemoryUsage =
+                AppContextConfigHelper.GetBooleanConfig("System.Threading.ThreadPool.Blocking.IgnoreMemoryUsage", false);
 
             public static readonly short ThreadsToAddWithoutDelay;
             public static readonly short ThreadsPerDelayStep;

src/libraries/System.Private.CoreLib/src/System/Threading/PortableThreadPool.GateThread.cs

@@ -36,7 +36,7 @@ private static void GateThreadStart()
                 LowLevelLock threadAdjustmentLock = threadPoolInstance._threadAdjustmentLock;
                 DelayHelper delayHelper = default;
 
-                if (BlockingConfig.IsCooperativeBlockingEnabled)
+                if (BlockingConfig.IsCooperativeBlockingEnabled && !BlockingConfig.IgnoreMemoryUsage)
                 {
                     // Initialize memory usage and limits, and register to update them on gen 2 GCs
                     threadPoolInstance.OnGen2GCCallback();

src/libraries/System.Threading.ThreadPool/tests/ThreadPoolTests.cs

@@ -906,7 +906,6 @@ public static void ThreadPoolThreadCreationDoesNotTransferExecutionContext()
         }
 
         [ConditionalFact(nameof(IsThreadingAndRemoteExecutorSupported))]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/66852", TestPlatforms.OSX)]
         public static void CooperativeBlockingCanCreateThreadsFaster()
         {
             // Run in a separate process to test in a clean thread pool environment such that work items queued by the test
@@ -924,6 +923,7 @@ public static void CooperativeBlockingCanCreateThreadsFaster()
                 int workItemCount = processorCount + 120;
                 SetBlockingConfigValue("ThreadsToAddWithoutDelay_ProcCountFactor", 1);
                 SetBlockingConfigValue("MaxDelayMs", 1);
+                SetBlockingConfigValue("IgnoreMemoryUsage", true);
 
                 var allWorkItemsUnblocked = new AutoResetEvent(false);
 
@@ -954,17 +954,19 @@ public static void CooperativeBlockingCanCreateThreadsFaster()
                     Assert.True(allWorkItemsUnblocked.WaitOne(30_000));
                 }
 
-                void SetBlockingConfigValue(string name, int value) =>
+                void SetBlockingConfigValue(string name, object value) =>
                     AppContextSetData("System.Threading.ThreadPool.Blocking." + name, value);
 
                 void AppContextSetData(string name, object value)
                 {
-                    typeof(AppContext).InvokeMember(
-                        "SetData",
-                        BindingFlags.ExactBinding | BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Static,
-                        null,
-                        null,
-                        new object[] { name, value });
+                    if (value is bool boolValue)
+                    {
+                        AppContext.SetSwitch(name, boolValue);
+                    }
+                    else
+                    {
+                        AppContext.SetData(name, value);
+                    }
                 }
             }).Dispose();
         }