Merge pull request #8695 from mono/nullability

[Core] Enable nullability analysis in MonoDevelop.Utilities

12 files changed, 139 insertions, 105 deletions

diff --git a/main/src/core/MonoDevelop.Core/CoreExtensions.EventHandlers.cs b/main/src/core/MonoDevelop.Core/CoreExtensions.EventHandlers.cs
index 9c526ba604..64a901b9d9 100644
--- a/main/src/core/MonoDevelop.Core/CoreExtensions.EventHandlers.cs
+++ b/main/src/core/MonoDevelop.Core/CoreExtensions.EventHandlers.cs
@@ -23,7 +23,8 @@
 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
-using System;
+#nullable enable
+
 using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
@@ -97,7 +98,7 @@ namespace System
 			}
 		}
 
-		static void TimeInvoke (Action<Delegate, object, EventArgs> call, Delegate[] del, object sender, EventArgs args, object groupId)
+		static void TimeInvoke (Action<Delegate, object, EventArgs> call, Delegate[] del, object sender, EventArgs args, object? groupId)
 		{
 			var sw = new Diagnostics.Stopwatch ();
 			foreach (var ev in del) {
@@ -113,7 +114,7 @@ namespace System
 			}
 		}
 
-		internal static void TimeInvoke<T> (this EventHandler<T> events, object sender, T args, object groupId = null) where T:EventArgs
+		internal static void TimeInvoke<T> (this EventHandler<T> events, object sender, T args, object? groupId = null) where T:EventArgs
 			=> TimeInvoke (
 				(del, s, a) => ((EventHandler<T>)del).Invoke (s, (T)a),
 				events.GetInvocationList (), // This can be a perf issue, do we have a different way to query it?
@@ -122,7 +123,7 @@ namespace System
 				groupId
 			);
 
-		internal static void TimeInvoke (this EventHandler events, object sender, EventArgs args, object groupId = null)
+		internal static void TimeInvoke (this EventHandler events, object sender, EventArgs args, object? groupId = null)
 			=> TimeInvoke (
 				(del, s, a) => ((EventHandler)del).Invoke (s, a),
 				events.GetInvocationList (), // This can be a perf issue, do we have a different way to query it?
diff --git a/main/src/core/MonoDevelop.Core/CoreExtensions.ReaderWriterLockSlim.cs b/main/src/core/MonoDevelop.Core/CoreExtensions.ReaderWriterLockSlim.cs
index b4805ff230..68131fd8e5 100644
--- a/main/src/core/MonoDevelop.Core/CoreExtensions.ReaderWriterLockSlim.cs
+++ b/main/src/core/MonoDevelop.Core/CoreExtensions.ReaderWriterLockSlim.cs
@@ -23,7 +23,7 @@
 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
-using System;
+#nullable enable
 using System.Threading;
 
 namespace System
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/BucketTimings.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/BucketTimings.cs
index 0f5c3f16b9..7182920407 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/BucketTimings.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/BucketTimings.cs
@@ -23,6 +23,9 @@
 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
+
+#nullable enable
+
 using System;
 using System.Collections.Immutable;
 
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/Counter.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/Counter.cs
index bcc3053bef..c383c38dde 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/Counter.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/Counter.cs
@@ -24,6 +24,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.IO;
@@ -38,12 +40,12 @@ namespace MonoDevelop.Core.Instrumentation
 		internal int totalCount;
 		string name;
 		bool logMessages;
-		CounterCategory category;
+		CounterCategory? category;
 		protected List<CounterValue> values = new List<CounterValue> ();
 		TimeSpan resolution = TimeSpan.FromMilliseconds (0);
 		DateTime lastValueTime = DateTime.MinValue;
 		bool disposed;
-		string id;
+		string? id;
 		
 		List<InstrumentationConsumer> handlers = new List<InstrumentationConsumer> ();
 
@@ -63,7 +65,7 @@ namespace MonoDevelop.Core.Instrumentation
 			InstrumentationService.InitializeHandlers ();
 		}
 	
-		internal Counter (string name, CounterCategory category)
+		internal Counter (string name, CounterCategory? category)
 		{
 			this.name = name;
 			this.category = category;
@@ -83,7 +85,7 @@ namespace MonoDevelop.Core.Instrumentation
 			internal set { id = value; }
 		}
 		
-		public CounterCategory Category {
+		public CounterCategory? Category {
 			get { return category; }
 		}
 		
@@ -178,7 +180,7 @@ namespace MonoDevelop.Core.Instrumentation
 			}
 		}
 		
-		internal int StoreValue (string message, ITimeCounter timer, IDictionary<string, object> metadata)
+		internal int StoreValue (string? message, ITimeCounter? timer, IDictionary<string, object>? metadata)
 		{
 			DateTime now = DateTime.Now;
 			if (resolution.Ticks != 0) {
@@ -222,7 +224,7 @@ namespace MonoDevelop.Core.Instrumentation
 			Inc (1, null);
 		}
 		
-		public void Inc (string message)
+		public void Inc (string? message)
 		{
 			Inc (1, message);
 		}
@@ -232,24 +234,24 @@ namespace MonoDevelop.Core.Instrumentation
 			Inc (n, null);
 		}
 
-		public void Inc (int n, string message)
+		public void Inc (int n, string? message)
 		{
-			Inc (n, message, (IDictionary<string, object>)null);
+			Inc (n, message, (IDictionary<string, object>?)null);
 		}
 
 		[Obsolete ("Use Inc (int, string, IDictionary<string, object>) instead")]
-		public void Inc (int n, string message, IDictionary<string, string> metadata)
+		public void Inc (int n, string? message, IDictionary<string, string>? metadata)
 		{
 			var converted = metadata.ToDictionary (k => k.Key, k => (object)k.Value);
 			Inc (n, message, converted);
 		}
 
-		public void Inc (IDictionary<string, object> metadata)
+		public void Inc (IDictionary<string, object>? metadata)
 		{
 			Inc (1, null, metadata);
 		}
 
-		public void Inc (int n, string message, IDictionary<string, object> metadata)
+		public void Inc (int n, string? message, IDictionary<string, object>? metadata)
 		{
 			if (Enabled) {
 				lock (values) {
@@ -277,12 +279,12 @@ namespace MonoDevelop.Core.Instrumentation
 			Dec (n, null);
 		}
 
-		public void Dec (int n, string message)
+		public void Dec (int n, string? message)
 		{
-			Dec (n, message, (IDictionary<string, object>)null); 
+			Dec (n, message, (IDictionary<string, object>?)null); 
 		}
 
-		public void Dec (int n, string message, IDictionary<string, object> metadata)
+		public void Dec (int n, string? message, IDictionary<string, object>? metadata)
 		{
 			if (Enabled) {
 				lock (values) {
@@ -299,12 +301,12 @@ namespace MonoDevelop.Core.Instrumentation
 			SetValue (value, null);
 		}
 
-		public void SetValue (int value, string message)
+		public void SetValue (int value, string? message)
 		{
-			SetValue (value, message, (IDictionary<string, object>)null);
+			SetValue (value, message, null);
 		}
 
-		public void SetValue (int value, string message, IDictionary<string, object> metadata)
+		public void SetValue (int value, string? message, IDictionary<string, object>? metadata)
 		{
 			if (Enabled) {
 				lock (values) {
@@ -339,14 +341,14 @@ namespace MonoDevelop.Core.Instrumentation
 		{
 			if (Enabled) {
 				lock (values) {
-					StoreValue (message, null, (IDictionary<string, object>)null);
+					StoreValue (message, null, null);
 				}
 			}
 			if (logMessages && message != null)
 				InstrumentationService.LogMessage (message);
 		}
 		
-		public override object InitializeLifetimeService ()
+		public override object? InitializeLifetimeService ()
 		{
 			return null;
 		}
@@ -403,15 +405,15 @@ namespace MonoDevelop.Core.Instrumentation
 	[Serializable]
 	public readonly struct CounterValue
 	{
-		readonly TimerTraceList traces;
-		readonly IDictionary<string, object> metadata;
+		readonly TimerTraceList? traces;
+		readonly IDictionary<string, object>? metadata;
 
-		internal CounterValue (int value, int totalCount, DateTime timestamp, IDictionary<string, object> metadata)
+		internal CounterValue (int value, int totalCount, DateTime timestamp, IDictionary<string, object>? metadata)
 			: this (value, totalCount, timestamp, null, null, metadata)
 		{
 		}
 
-		internal CounterValue (int value, int totalCount, DateTime timestamp, string message, TimerTraceList traces, IDictionary<string, object> metadata)
+		internal CounterValue (int value, int totalCount, DateTime timestamp, string? message, TimerTraceList? traces, IDictionary<string, object>? metadata)
 		{
 			Value = value;
 			TimeStamp = timestamp;
@@ -430,11 +432,11 @@ namespace MonoDevelop.Core.Instrumentation
 
 		public int ThreadId { get; }
 
-		public string Message { get; }
+		public string? Message { get; }
 
 		public bool HasTimerTraces => traces != null;
 
-		public IDictionary<string, object> Metadata {
+		public IDictionary<string, object>? Metadata {
 			get {
 				// If the value is for a timer, metadata will be stored in the traces list.
 				// That's because metadata may be allocated after CounterValue has been
@@ -447,7 +449,7 @@ namespace MonoDevelop.Core.Instrumentation
 		
 		public IEnumerable<TimerTrace> GetTimerTraces ()
 		{
-			TimerTrace trace = traces?.FirstTrace;
+			TimerTrace? trace = traces?.FirstTrace;
 			while (trace != null) {
 				yield return trace;
 				trace = trace.Next;
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/CounterCategory.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/CounterCategory.cs
index d18026491b..fc9a2ebffe 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/CounterCategory.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/CounterCategory.cs
@@ -24,6 +24,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/InstrumentationConsumer.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/InstrumentationConsumer.cs
index 344a786516..6456c35a50 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/InstrumentationConsumer.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/InstrumentationConsumer.cs
@@ -23,6 +23,9 @@
 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
+
+#nullable enable
+
 using System;
 
 namespace MonoDevelop.Core.Instrumentation
@@ -55,7 +58,7 @@ namespace MonoDevelop.Core.Instrumentation
 		/// <returns>An IDisposable object that is disposed when the timing operation ends.</returns>
 		/// <param name="counter">The timer counter</param>
 		/// <param name="value">The value</param>
-		public virtual IDisposable BeginTimer (TimerCounter counter, CounterValue value)
+		public virtual IDisposable? BeginTimer (TimerCounter counter, CounterValue value)
 		{
 			return null;
 		}
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/InstrumentationService.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/InstrumentationService.cs
index dfee0cc691..c034c4abdf 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/InstrumentationService.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/InstrumentationService.cs
@@ -24,6 +24,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
+#nullable enable
+
 using System;
 using System.IO;
 using System.Collections.Generic;
@@ -54,7 +56,7 @@ namespace MonoDevelop.Core.Instrumentation
 		static bool enabled = true;
 		static DateTime startTime = DateTime.Now;
 		static int publicPort = -1;
-		static Thread autoSaveThread;
+		static Thread? autoSaveThread;
 		static bool stopping;
 		static int autoSaveInterval;
 		static bool handlersLoaded;
@@ -206,11 +208,9 @@ namespace MonoDevelop.Core.Instrumentation
 
 		public static IInstrumentationService GetServiceData ()
 		{
-			return new InstrumentationServiceData {
+			return new InstrumentationServiceData (counters, categories) {
 				EndTime = DateTime.Now,
 				StartTime = StartTime,
-				Counters = counters,
-				Categories = categories
 			};
 		}
 		
@@ -244,32 +244,32 @@ namespace MonoDevelop.Core.Instrumentation
 			return CreateCounter (name, null);
 		}
 		
-		public static Counter CreateCounter (string name, string category)
+		public static Counter CreateCounter (string name, string? category)
 		{
 			return CreateCounter (name, category, false);
 		}
 		
-		public static Counter CreateCounter (string name, string category, bool logMessages)
+		public static Counter CreateCounter (string name, string? category, bool logMessages)
 		{
 			return CreateCounter (name, category, logMessages, null, false);
 		}
 		
-		public static Counter CreateCounter (string name, string category = null, bool logMessages = false, string id = null)
+		public static Counter CreateCounter (string name, string? category = null, bool logMessages = false, string? id = null)
 		{
 			return CreateCounter (name, category, logMessages, id, false);
 		}
 
-		public static Counter<T> CreateCounter<T> (string name, string category = null, bool logMessages = false, string id = null) where T : CounterMetadata, new()
+		public static Counter<T> CreateCounter<T> (string name, string? category = null, bool logMessages = false, string? id = null) where T : CounterMetadata, new()
 		{
 			return (Counter<T>) CreateCounter<T> (name, category, logMessages, id, false);
 		}
 
-		static Counter CreateCounter (string name, string category, bool logMessages, string id, bool isTimer)
+		static Counter CreateCounter (string name, string? category, bool logMessages, string? id, bool isTimer)
 		{
 			return CreateCounter<CounterMetadata> (name, category, logMessages, id, isTimer);
 		}
 
-		static Counter CreateCounter<T> (string name, string category, bool logMessages, string id, bool isTimer) where T:CounterMetadata, new()
+		static Counter CreateCounter<T> (string name, string? category, bool logMessages, string? id, bool isTimer) where T:CounterMetadata, new()
 		{
 			if (name == null)
 				throw new ArgumentNullException ("name", "Counters must have a Name");
@@ -280,14 +280,14 @@ namespace MonoDevelop.Core.Instrumentation
 				category = "Global";
 				
 			lock (counters) {
-				CounterCategory cat = GetCategory (category);
+				CounterCategory? cat = GetCategory (category);
 				if (cat == null) {
 					cat = new CounterCategory (category);
 					categories.Add (cat);
 				}
 				
 				var c = isTimer ? new TimerCounter<T> (name, cat) : (Counter) new Counter<T> (name, cat);
-				c.Id = id;
+				c.Id = id!;
 				c.LogMessages = logMessages;
 				cat.AddCounter (c);
 				
@@ -296,7 +296,7 @@ namespace MonoDevelop.Core.Instrumentation
 					old.Disposed = true;
 				counters [name] = c;
 				if (!string.IsNullOrEmpty (id)) {
-					countersByID [id] = c;
+					countersByID [id!] = c;
 				}
 
 				foreach (var h in handlers) {
@@ -309,12 +309,12 @@ namespace MonoDevelop.Core.Instrumentation
 			}
 		}
 		
-		public static MemoryProbe CreateMemoryProbe (string name)
+		public static MemoryProbe? CreateMemoryProbe (string name)
 		{
 			return CreateMemoryProbe (name, null);
 		}
 		
-		public static MemoryProbe CreateMemoryProbe (string name, string category)
+		public static MemoryProbe? CreateMemoryProbe (string name, string? category)
 		{
 			if (!enabled)
 				return null;
@@ -332,17 +332,13 @@ namespace MonoDevelop.Core.Instrumentation
 			return CreateTimerCounter (name, null);
 		}
 		
-		public static TimerCounter CreateTimerCounter (string name, string category)
+		public static TimerCounter CreateTimerCounter (string name, string? category)
 		{
 			return CreateTimerCounter (name, category, 0, false);
 		}
 		
-		public static TimerCounter CreateTimerCounter (string name, string category, double minSeconds, bool logMessages)
-		{
-			return CreateTimerCounter (name, category, minSeconds, logMessages, null);
-		}
 
-		public static TimerCounter CreateTimerCounter (string name, string category = null, double minSeconds = 0, bool logMessages = false, string id = null)
+		public static TimerCounter CreateTimerCounter (string name, string? category = null, double minSeconds = 0, bool logMessages = false, string? id = null)
 		{
 			TimerCounter c = (TimerCounter) CreateCounter (name, category, logMessages, id, true);
 			c.LogMessages = logMessages;
@@ -350,7 +346,7 @@ namespace MonoDevelop.Core.Instrumentation
 			return c;
 		}
 		
-		public static TimerCounter<T> CreateTimerCounter<T> (string name, string category = null, double minSeconds = 0, bool logMessages = false, string id = null) where T:CounterMetadata, new()
+		public static TimerCounter<T> CreateTimerCounter<T> (string name, string? category = null, double minSeconds = 0, bool logMessages = false, string? id = null) where T:CounterMetadata, new()
 		{
 			var c = (TimerCounter<T>) CreateCounter<T> (name, category, logMessages, id, true);
 			c.LogMessages = logMessages;
@@ -381,7 +377,7 @@ namespace MonoDevelop.Core.Instrumentation
 			}
 		}
 
-		public static CounterCategory GetCategory (string name)
+		public static CounterCategory? GetCategory (string name)
 		{
 			lock (counters) {
 				foreach (CounterCategory cat in categories)
@@ -437,7 +433,7 @@ namespace MonoDevelop.Core.Instrumentation
 	class IntrumentationMonitor: ProgressMonitor
 	{
 		TimerCounter counter;
-		Stack<ITimeTracker> timers = new Stack<ITimeTracker> ();
+		Stack<ITimeTracker?> timers = new Stack<ITimeTracker?> ();
 
 		public IntrumentationMonitor (TimerCounter counter)
 		{
@@ -447,7 +443,7 @@ namespace MonoDevelop.Core.Instrumentation
 		protected override void OnWriteLog (string message)
 		{
 			if (timers.Count > 0)
-				timers.Peek ().Trace (message);
+				timers.Peek ()?.Trace (message);
 		}
 
 		protected override void OnBeginTask (string name, int totalWork, int stepWork)
@@ -464,7 +460,7 @@ namespace MonoDevelop.Core.Instrumentation
 		protected override void OnEndTask (string name, int totalWork, int stepWork)
 		{
 			if (timers.Count > 0) {
-				ITimeTracker c = timers.Pop ();
+				ITimeTracker? c = timers.Pop ();
 				if (c != null)
 					c.End ();
 			}
@@ -477,7 +473,7 @@ namespace MonoDevelop.Core.Instrumentation
 		DateTime EndTime { get; }
 		IEnumerable<Counter> GetCounters ();
 		Counter GetCounter (string name);
-		CounterCategory GetCategory (string name);
+		CounterCategory? GetCategory (string name);
 		IEnumerable<CounterCategory> GetCategories ();
 	}
 	
@@ -505,7 +501,7 @@ namespace MonoDevelop.Core.Instrumentation
 			return InstrumentationService.GetCounter (name);
 		}
 		
-		public CounterCategory GetCategory (string name)
+		public CounterCategory? GetCategory (string name)
 		{
 			return InstrumentationService.GetCategory (name);
 		}
@@ -515,7 +511,7 @@ namespace MonoDevelop.Core.Instrumentation
 			return InstrumentationService.GetCategories ();
 		}
 		
-		public override object InitializeLifetimeService ()
+		public override object? InitializeLifetimeService ()
 		{
 			return null;
 		}
@@ -526,8 +522,14 @@ namespace MonoDevelop.Core.Instrumentation
 	{
 		public DateTime StartTime { get; set; }
 		public DateTime EndTime { get; set; }
-		public Dictionary <string, Counter> Counters { get; set; }
-		public List<CounterCategory> Categories { get; set; }
+		public Dictionary <string, Counter> Counters { get; }
+		public List<CounterCategory> Categories { get; }
+
+		public InstrumentationServiceData (Dictionary<string, Counter> counters, List<CounterCategory> categories)
+		{
+			Counters = counters;
+			Categories = categories;
+		}
 		
 		public IEnumerable<Counter> GetCounters ()
 		{
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/MemoryProbe.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/MemoryProbe.cs
index a0f7c58d03..784aaed430 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/MemoryProbe.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/MemoryProbe.cs
@@ -24,13 +24,15 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
+#nullable enable
+
 using System;
 
 namespace MonoDevelop.Core.Instrumentation
 {
 	public class MemoryProbe
 	{
-		Counter c;
+		readonly Counter c;
 		
 		public MemoryProbe (Counter c)
 		{
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/TimeCounter.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/TimeCounter.cs
index 833cc45079..130f28ac79 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/TimeCounter.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/TimeCounter.cs
@@ -24,6 +24,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -41,18 +43,18 @@ namespace MonoDevelop.Core.Instrumentation
 	
 	public interface ITimeTracker<T>: IDisposable, ITimeTracker where T : CounterMetadata
 	{
-		T Metadata { get; }
+		T? Metadata { get; }
 	}
 
 	interface ITimeCounter: ITimeTracker
 	{
 		void AddHandlerTracker (IDisposable t);
-		TimerTraceList TraceList { get; }
+		TimerTraceList? TraceList { get; }
 	}
 	
 	class DummyTimerCounter<T>: ITimeTracker<T> where T : CounterMetadata
 	{
-		public DummyTimerCounter (T metadata)
+		public DummyTimerCounter (T? metadata)
 		{
 			Metadata = metadata;
 		}
@@ -69,23 +71,23 @@ namespace MonoDevelop.Core.Instrumentation
 		{
 		}
 
-		public T Metadata { get; }
+		public T? Metadata { get; }
 
 		public TimeSpan Duration { get; }
 	}
 	
 	class TimeCounter<T>: ITimeTracker<T>, ITimeCounter where T:CounterMetadata, new()
 	{
-		Stopwatch stopWatch = new Stopwatch ();
-		TimerTraceList traceList;
-		TimerTrace lastTrace;
-		TimerCounter counter;
-		object linkedTrackers;
+		readonly Stopwatch stopWatch = new Stopwatch ();
+		TimerTraceList? traceList;
+		TimerTrace? lastTrace;
+		TimerCounter? counter;
+		object? linkedTrackers;
 		long lastTraceTime;
-		T metadata;
+		T? metadata;
 		CancellationToken cancellationToken;
 
-		internal TimeCounter (TimerCounter counter, T metadata, CancellationToken cancellationToken)
+		internal TimeCounter (TimerCounter counter, T? metadata, CancellationToken cancellationToken)
 		{
 			this.counter = counter;
 			this.metadata = metadata;
@@ -123,7 +125,7 @@ namespace MonoDevelop.Core.Instrumentation
 				((List<IDisposable>)linkedTrackers).Add (t);
 		}
 		
-		TimerTraceList ITimeCounter.TraceList {
+		TimerTraceList? ITimeCounter.TraceList {
 			get { return this.traceList; }
 		}
 		
@@ -139,7 +141,7 @@ namespace MonoDevelop.Core.Instrumentation
 					lastTrace.Next = t;
 					lastTrace = t;
 				}
-				traceList.TotalTime = t.Timestamp - traceList.FirstTrace.Timestamp;
+				traceList.TotalTime = t.Timestamp - traceList.FirstTrace!.Timestamp;
 			}
 			if (counter?.LogMessages == true) {
 				var time = stopWatch.ElapsedMilliseconds;
@@ -166,7 +168,7 @@ namespace MonoDevelop.Core.Instrumentation
 			if (metadata != null && cancellationToken.IsCancellationRequested)
 				metadata.SetUserCancel ();
 
-			if (counter.LogMessages) {
+			if (counter!.LogMessages) {
 				var time = stopWatch.ElapsedMilliseconds;
 				InstrumentationService.LogMessage (string.Format ("[{0} (+{1})] END: {2}", time, (time - lastTraceTime), counter.Name));
 			}
@@ -201,19 +203,19 @@ namespace MonoDevelop.Core.Instrumentation
 	[DebuggerDisplay ("{DebuggingText}")]
 	class TimerTraceList
 	{
-		public TimerTrace FirstTrace;
+		public TimerTrace? FirstTrace;
 		public TimeSpan TotalTime;
 		public int ValueIndex;
 
 		// Timer metadata is stored here, since it may change while the timer is alive.
 		// CounterValue will take the metadata from here.
-		public IDictionary<string, object> Metadata;
+		public IDictionary<string, object>? Metadata;
 
 		string DebuggingText {
 			get {
 				var stringBuilder = new StringBuilder ();
 				var current = FirstTrace;
-				TimerTrace previous = null;
+				TimerTrace? previous = null;
 				while (current != null) {
 					stringBuilder.Append (previous == null ? "N/A" : (current.Timestamp - previous.Timestamp).ToString (@"ss\.fff"));
 					stringBuilder.Append (" : ");
@@ -229,8 +231,8 @@ namespace MonoDevelop.Core.Instrumentation
 	[Serializable]
 	public class TimerTrace
 	{
-		internal TimerTrace Next;
+		internal TimerTrace? Next;
 		public DateTime Timestamp { get; set; }
-		public string Message { get; set; }
+		public string? Message { get; set; }
 	}
 }
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/TimerCounter.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/TimerCounter.cs
index c5ed3fd66a..a3414ac9e7 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/TimerCounter.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.Instrumentation/TimerCounter.cs
@@ -24,6 +24,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
+#nullable enable
+
 using System;
 using System.Collections.Generic;
 using System.Threading;
@@ -93,27 +95,27 @@ namespace MonoDevelop.Core.Instrumentation
 
 		public ITimeTracker BeginTiming ()
 		{
-			return BeginTiming (null, (IDictionary<string, object>)null);
+			return BeginTiming (null, null);
 		}
 
 		public ITimeTracker BeginTiming (string message)
 		{
-			return BeginTiming (message, (IDictionary<string, object>)null);
+			return BeginTiming (message, null);
 		}
 
 		[Obsolete ("Use BeginTiming (string, IDictionary<string,object>) instead")]
-		public ITimeTracker BeginTiming (IDictionary<string, string> metadata)
+		public ITimeTracker BeginTiming (IDictionary<string, string>? metadata)
 		{
 			var converted = metadata.ToDictionary (k => k.Key, k => (object)(k.Value));
 			return BeginTiming (null, converted);
 		}
 
-		public ITimeTracker BeginTiming (string message, IDictionary<string, object> metadata)
+		public ITimeTracker BeginTiming (string? message, IDictionary<string, object>? metadata)
 		{
 			return BeginTiming (message, metadata != null ? new CounterMetadata (metadata) : null, CancellationToken.None);
 		}
 
-		internal ITimeTracker<T> BeginTiming<T> (string message, T metadata, CancellationToken cancellationToken) where T : CounterMetadata, new()
+		internal ITimeTracker<T> BeginTiming<T> (string? message, T? metadata, CancellationToken cancellationToken) where T : CounterMetadata, new()
 		{
 			if (!Enabled && !LogMessages) {
 				return new DummyTimerCounter<T> (metadata);
@@ -126,7 +128,10 @@ namespace MonoDevelop.Core.Instrumentation
 					count++;
 					totalCount++;
 					int i = StoreValue (message, c, metadata?.Properties);
-					((ITimeCounter)c).TraceList.ValueIndex = i;
+
+					var traceList = ((ITimeCounter)c).TraceList;
+					if (traceList != null)
+						traceList.ValueIndex = i;
 				}
 			} else {
 				if (message != null)
@@ -231,11 +236,20 @@ namespace MonoDevelop.Core.Instrumentation
 		public void SetSuccess () => Result = CounterResult.Success;
 		public void SetUserCancel () => Result = CounterResult.UserCancel;
 
-		protected void SetProperty (object value, [CallerMemberName]string name = null)
-			=> Properties[name] = value;
+		protected void SetProperty (object value, [CallerMemberName]string? name = null)
+		{
+			if (name == null)
+				throw new ArgumentNullException (nameof (name));
 
-		protected T GetProperty<T> ([CallerMemberName]string name = null)
+			Properties [name] = value;
+		}
+
+		// [return: MaybeNull]
+		protected T GetProperty<T> ([CallerMemberName]string? name = null)
 		{
+			if (name == null)
+				throw new ArgumentNullException (nameof (name));
+
 			if (Properties.TryGetValue (name, out var result)) {
 				return (T)Convert.ChangeType (result, typeof (T), CultureInfo.InvariantCulture);
 			}
@@ -243,8 +257,11 @@ namespace MonoDevelop.Core.Instrumentation
 			return default (T);
 		}
 
-		protected bool ContainsProperty ([CallerMemberName]string propName = null)
+		protected bool ContainsProperty ([CallerMemberName]string? propName = null)
 		{
+			if (propName == null)
+				throw new ArgumentNullException (nameof (propName));
+
 			return Properties.ContainsKey (propName);
 		}
 	}
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Utilities/RaceChecker.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Utilities/RaceChecker.cs
index 0c4e11d1ca..28880efdcc 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Utilities/RaceChecker.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Utilities/RaceChecker.cs
@@ -23,6 +23,8 @@
 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
+#nullable enable
+
 using System;
 using System.Threading;
 using MonoDevelop.Core;
@@ -31,7 +33,7 @@ namespace MonoDevelop.Utilities
 {
 	abstract class RaceChecker
 	{
-		string lockHolderStacktrace;
+		string? lockHolderStacktrace;
 		readonly object lockObject;
 		readonly Disposer lockRelease;
 
@@ -48,7 +50,7 @@ namespace MonoDevelop.Utilities
 			} else {
 				Monitor.Enter (lockObject);
 				var thisTrace = Environment.StackTrace;
-				OnRace (lockHolderStacktrace, thisTrace);
+				OnRace (lockHolderStacktrace!, thisTrace);
 				lockHolderStacktrace = thisTrace;
 			}
 
@@ -57,7 +59,7 @@ namespace MonoDevelop.Utilities
 
 		protected abstract void OnRace (string trace1, string trace2);
 
-		class Disposer : IDisposable
+		sealed class Disposer : IDisposable
 		{
 			readonly object lockObject;
 
@@ -74,7 +76,7 @@ namespace MonoDevelop.Utilities
 		}
 	}
 
-	class LoggingRaceChecker : RaceChecker
+	sealed class LoggingRaceChecker : RaceChecker
 	{
 		protected override void OnRace (string trace1, string trace2)
 		{
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Utilities/SampleProfiler.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Utilities/SampleProfiler.cs
index 2a8f1cfa93..cfe52cf559 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Utilities/SampleProfiler.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Utilities/SampleProfiler.cs
@@ -23,11 +23,10 @@
 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
+#nullable enable
+
 using System;
-using System.Net.Sockets;
-using System.Net;
 using System.Diagnostics;
-using System.Threading;
 using MonoDevelop.Core;
 using System.IO;
 using System.Runtime.InteropServices;
@@ -35,7 +34,6 @@ using System.Text.RegularExpressions;
 using System.Globalization;
 using System.Collections.Generic;
 using System.Text;
-using System.Threading.Tasks;
 
 namespace MonoDevelop.Utilities
 {
@@ -111,7 +109,7 @@ namespace MonoDevelop.Utilities
 
 		[DllImport ("__Internal")]
 		extern static string mono_pmip (long offset);
-		readonly static Dictionary<long, string> methodsCache = new Dictionary<long, string> ();
+		readonly static Dictionary<long, string?> methodsCache = new Dictionary<long, string?> ();
 
 		public static void ConvertJITAddressesToMethodNames (string outputPath, string fileName, string profilingType)
 		{
@@ -167,9 +165,9 @@ namespace MonoDevelop.Utilities
 				}
 			}
 
-			static string GetSymbolicatedLine (long offset)
+			static string? GetSymbolicatedLine (long offset)
 			{
-				if (!methodsCache.TryGetValue (offset, out var pmipMethodName)) {
+				if (!methodsCache.TryGetValue (offset, out string? pmipMethodName)) {
 					pmipMethodName = mono_pmip (offset)?.TrimStart ();
 					if (pmipMethodName != null)
 						pmipMethodName = PmipParser.ToSample (pmipMethodName, offset);
@@ -194,7 +192,6 @@ namespace MonoDevelop.Utilities
 				try {
 					var input = initialInput.AsSpan ();
 					var sb = new StringBuilder ();
-					string filename = null;
 
 					// Cut off wrapper part.
 					if (input.StartsWith ("(wrapper".AsSpan ())) {
@@ -249,6 +246,7 @@ namespace MonoDevelop.Utilities
 					// Skip the rest of the block(s) after the method signature until we get a path.
 					input = input.Slice (input.IndexOf ('[') + 1).TrimStart ();
 
+					string? filename = null;
 					if (input[0] == '/') {
 						// We have a filename
 						var end = input.IndexOf (']');