address PR feedback

src/DurableTask.Netherite/OrchestrationService/Partition.cs

@@ -55,7 +55,10 @@ namespace DurableTask.Netherite
         // A little helper property that allows us to conventiently check the condition for low-level event tracing
         public EventTraceHelper EventDetailTracer => this.EventTraceHelper.IsTracingAtMostDetailedLevel ? this.EventTraceHelper : null;
 
-        static readonly SemaphoreSlim MaxConcurrentStarts = new SemaphoreSlim(5);
+        // We use this semaphore to limit how many partitions can be starting up at the same time on the same host
+        // because starting up a partition may temporarily consume a lot of CPU, I/O, and memory
+        const int ConcurrentStartsLimit = 5;
+        static readonly SemaphoreSlim MaxConcurrentStarts = new SemaphoreSlim(ConcurrentStartsLimit);
 
         public Partition(
             NetheriteOrchestrationService host,
@@ -108,7 +111,7 @@ namespace DurableTask.Netherite
 
             // before we start the partition, we have to acquire the MaxConcurrentStarts semaphore
             // (to prevent a host from being overwhelmed by the simultaneous start of too many partitions)
-            this.TraceHelper.TracePartitionProgress("Waiting", ref this.LastTransition, this.CurrentTimeMs, "");
+            this.TraceHelper.TracePartitionProgress("Waiting", ref this.LastTransition, this.CurrentTimeMs, $"max={ConcurrentStartsLimit} available={MaxConcurrentStarts.CurrentCount}");
             await MaxConcurrentStarts.WaitAsync();
 
             try
@@ -117,9 +120,8 @@ namespace DurableTask.Netherite
 
                 (long, int) inputQueuePosition;
 
-                using (new PartitionTimeout(errorHandler, "partition startup", TimeSpan.FromMinutes(this.Settings.PartitionStartupTimeoutMinutes)))
+                await using (new PartitionTimeout(errorHandler, "partition startup", TimeSpan.FromMinutes(this.Settings.PartitionStartupTimeoutMinutes)))
                 {
-
                     // create or restore partition state from last snapshot
                     // create the state
                     this.State = ((TransportAbstraction.IHost)this.host).StorageLayer.CreatePartitionState(parameters);

src/DurableTask.Netherite/Util/PartitionTimeout.cs

@@ -11,9 +11,9 @@ namespace DurableTask.Netherite
 
     /// <summary>
     /// A utility class for terminating the partition if some task takes too long.
-    /// Implemented as a disposable, with <see cref="IDisposable.Dispose"> used to cancel the timeout.
+    /// Implemented as a disposable, with <see cref="IAsyncDisposable.DisposeAsync"> used to cancel the timeout.
     /// </summary>
-    class PartitionTimeout : IDisposable
+    class PartitionTimeout : IAsyncDisposable
     {
         readonly CancellationTokenSource tokenSource;
         readonly Task timeoutTask;
@@ -21,26 +21,39 @@ namespace DurableTask.Netherite
         public PartitionTimeout(IPartitionErrorHandler errorHandler, string task, TimeSpan timeout)
         {
             this.tokenSource = new CancellationTokenSource();
-            this.timeoutTask = Task.Delay(timeout, this.tokenSource.Token);
+            this.timeoutTask = Task.Run(async () =>
+            {
+                try
+                {
+                    await Task.Delay(timeout, this.tokenSource.Token).ConfigureAwait(false);
+                }
+                catch (OperationCanceledException)
+                {
+                    // we did not time out
+                    return;
+                }
 
-            // if the timeout tasks runs to completion without being cancelled, terminate the partition
-            this.timeoutTask.ContinueWith(
-                 _ => errorHandler.HandleError(
-                     $"{nameof(PartitionTimeout)}",
-                     $"{task} timed out after {timeout}",
-                     e: null,
-                     terminatePartition: true,
-                     reportAsWarning: false),
-                 TaskContinuationOptions.OnlyOnRanToCompletion);
+                errorHandler.HandleError(
+                    $"{nameof(PartitionTimeout)}",
+                    $"{task} timed out after {timeout}",
+                    e: null,
+                    terminatePartition: true,
+                    reportAsWarning: false);
+            });
         }
 
-        public void Dispose()
+        public async ValueTask DisposeAsync()
         {      
             // cancel the timeout task (if it has not already completed)
             this.tokenSource.Cancel();
 
-            // dispose the token source after the timeout task has completed
-            this.timeoutTask.ContinueWith(_ => this.tokenSource.Dispose());
+            // wait for the timeouttask to complete here, so we can be sure that the
+            // decision about the timeout firing or not firing has been made
+            // before we leave this method
+            await this.timeoutTask.ConfigureAwait(false);
+
+            // we can dispose the token source now since the timeoutTask is completed
+            this.tokenSource.Dispose();
         }
     }
 }