Fix OS-level thread priority degradation in InProcess executors

Author: cloudsealed

src/BenchmarkDotNet/Toolchains/InProcess/Emit/InProcessEmitExecutor.cs

@@ -70,10 +70,12 @@ private async ValueTask<int> ExecuteCore(IHost host, ExecuteParameters parameter
             var oldThreadPriority = thread.Priority;
 
             var affinity = parameters.BenchmarkCase.Job.ResolveValueAsNullable(EnvironmentMode.AffinityCharacteristic);
+            bool processPrioritySet = false;
+            bool threadPrioritySet = false;
             try
             {
-                process.TrySetPriority(ProcessPriorityClass.High, parameters.Logger);
-                thread.TrySetPriority(ThreadPriority.Highest, parameters.Logger);
+                processPrioritySet = process.TrySetPriority(ProcessPriorityClass.High, parameters.Logger);
+                threadPrioritySet = thread.TrySetPriority(ThreadPriority.Highest, parameters.Logger);
 
                 if (affinity != null)
                 {
@@ -88,8 +90,10 @@ private async ValueTask<int> ExecuteCore(IHost host, ExecuteParameters parameter
             }
             finally
             {
-                process.TrySetPriority(oldPriority, parameters.Logger);
-                thread.TrySetPriority(oldThreadPriority, parameters.Logger);
+                if (processPrioritySet)
+                    process.TrySetPriority(oldPriority, parameters.Logger);
+                if (threadPrioritySet)
+                    thread.TrySetPriority(oldThreadPriority, parameters.Logger);
 
                 if (affinity != null && oldAffinity != null)
                 {

src/BenchmarkDotNet/Toolchains/InProcess/NoEmit/InProcessNoEmitExecutor.cs

@@ -71,10 +71,12 @@ private async ValueTask<int> ExecuteCore(IHost host, ExecuteParameters parameter
             var oldThreadPriority = thread.Priority;
 
             var affinity = parameters.BenchmarkCase.Job.ResolveValueAsNullable(EnvironmentMode.AffinityCharacteristic);
+            bool processPrioritySet = false;
+            bool threadPrioritySet = false;
             try
             {
-                process.TrySetPriority(ProcessPriorityClass.High, parameters.Logger);
-                thread.TrySetPriority(ThreadPriority.Highest, parameters.Logger);
+                processPrioritySet = process.TrySetPriority(ProcessPriorityClass.High, parameters.Logger);
+                threadPrioritySet = thread.TrySetPriority(ThreadPriority.Highest, parameters.Logger);
 
                 if (affinity != null)
                 {
@@ -89,8 +91,10 @@ private async ValueTask<int> ExecuteCore(IHost host, ExecuteParameters parameter
             }
             finally
             {
-                process.TrySetPriority(oldPriority, parameters.Logger);
-                thread.TrySetPriority(oldThreadPriority, parameters.Logger);
+                if (processPrioritySet)
+                    process.TrySetPriority(oldPriority, parameters.Logger);
+                if (threadPrioritySet)
+                    thread.TrySetPriority(oldThreadPriority, parameters.Logger);
 
                 if (affinity != null && oldAffinity != null)
                 {