Add ReadyToCompletePendingAsync for client to check if there is somet… (

#269)

* Add ReadyToCompletePendingAsync for client to check if there is something to complete-pending on.

* Updates

cs/src/core/ClientSession/ClientSession.cs

@@ -310,7 +310,8 @@ public void Refresh()
         }
 
         /// <summary>
-        /// Sync complete outstanding pending operations
+        /// Sync complete all outstanding pending operations
+        /// Async operations (ReadAsync) must be completed individually
         /// </summary>
         /// <param name="spinWait">Spin-wait for all pending operations on session to complete</param>
         /// <param name="spinWaitForCommit">Extend spin-wait until ongoing commit/checkpoint, if any, completes</param>
@@ -365,6 +366,22 @@ public async ValueTask CompletePendingAsync(bool waitForCommit = false, Cancella
                 await WaitForCommitAsync(token);
         }
 
+        /// <summary>
+        /// Check if at least one request is ready for CompletePending to be called on
+        /// Returns completed immediately if there are no outstanding requests
+        /// </summary>
+        /// <param name="token"></param>
+        /// <returns></returns>
+        public async ValueTask ReadyToCompletePendingAsync(CancellationToken token = default)
+        {
+            token.ThrowIfCancellationRequested();
+
+            if (fht.epoch.ThisInstanceProtected())
+                throw new NotSupportedException("Async operations not supported over protected epoch");
+
+            await fht.ReadyToCompletePendingAsync(this, token);
+        }
+
         /// <summary>
         /// Wait for commit of all operations completed until the current point in session.
         /// Does not itself issue checkpoint/commits.

cs/src/core/ClientSession/FASTERAsync.cs

@@ -26,6 +26,30 @@ public partial class FasterKV<Key, Value, Input, Output, Context, Functions> : F
         where Value : new()
         where Functions : IFunctions<Key, Value, Input, Output, Context>
     {
+
+        /// <summary>
+        /// Check if at least one (sync) request is ready for CompletePending to operate on
+        /// </summary>
+        /// <param name="clientSession"></param>
+        /// <param name="token"></param>
+        /// <returns></returns>
+        internal async ValueTask ReadyToCompletePendingAsync(ClientSession<Key, Value, Input, Output, Context, Functions> clientSession, CancellationToken token = default)
+        {
+            #region Previous pending requests
+            if (!RelaxedCPR)
+            {
+                if (clientSession.ctx.phase == Phase.IN_PROGRESS || clientSession.ctx.phase == Phase.WAIT_PENDING)
+                {
+                    if (clientSession.ctx.prevCtx.SyncIoPendingCount != 0)
+                        await clientSession.ctx.prevCtx.readyResponses.WaitForEntryAsync(token);
+                }
+            }
+            #endregion
+
+            if (clientSession.ctx.SyncIoPendingCount != 0)
+                await clientSession.ctx.readyResponses.WaitForEntryAsync(token);
+        }
+
         /// <summary>
         /// Complete outstanding pending operations that were issued synchronously
         /// Async operations (e.g., ReadAsync) need to be completed individually
@@ -46,7 +70,7 @@ internal async ValueTask CompletePendingAsync(ClientSession<Key, Value, Input, O
                     await clientSession.ctx.prevCtx.pendingReads.WaitEmptyAsync();
 
                     await InternalCompletePendingRequestsAsync(clientSession.ctx.prevCtx, clientSession.ctx, clientSession, token);
-                    Debug.Assert(clientSession.ctx.prevCtx.ioPendingRequests.Count == 0);
+                    Debug.Assert(clientSession.ctx.prevCtx.SyncIoPendingCount == 0);
 
                     if (clientSession.ctx.prevCtx.retryRequests.Count > 0)
                     {
@@ -106,7 +130,7 @@ internal ReadAsyncInternal(FasterKV<Key, Value, Input, Output, Context, Function
                         {
                             Debug.Assert(_fasterKV.RelaxedCPR);
 
-                            _result = _fasterKV.InternalCompletePendingReadRequestAsync(
+                            _result = _fasterKV.InternalCompletePendingReadRequest(
                                 _clientSession.ctx, _clientSession.ctx, _diskRequest, _pendingContext);
                         }
                         finally
@@ -121,6 +145,7 @@ internal ReadAsyncInternal(FasterKV<Key, Value, Input, Output, Context, Function
                     finally
                     {
                         _clientSession.ctx.ioPendingRequests.Remove(_pendingContext.id);
+                        _clientSession.ctx.asyncPendingCount--;
                     }
                 }
 
@@ -212,6 +237,7 @@ static async ValueTask<ReadAsyncResult> SlowReadAsync(
             {
                 var diskRequest = @this.ScheduleGetFromDisk(clientSession.ctx, ref pendingContext);
                 clientSession.ctx.ioPendingRequests.Add(pendingContext.id, pendingContext);
+                clientSession.ctx.asyncPendingCount++;
                 clientSession.ctx.pendingReads.Add();
 
                 try
@@ -226,6 +252,7 @@ static async ValueTask<ReadAsyncResult> SlowReadAsync(
                 catch
                 {
                     clientSession.ctx.ioPendingRequests.Remove(pendingContext.id);
+                    clientSession.ctx.asyncPendingCount--;
                     throw;
                 }
                 finally 

cs/src/core/Index/Common/Contexts.cs

@@ -103,14 +103,16 @@ internal sealed class FasterExecutionContext : SerializedFasterExecutionContext
             public AsyncCountDown pendingReads;
             public AsyncQueue<AsyncIOContext<Key, Value>> readyResponses;
             public List<long> excludedSerialNos;
+            public int asyncPendingCount;
+
+            public int SyncIoPendingCount => ioPendingRequests.Count - asyncPendingCount;
 
             public bool HasNoPendingRequests
             {
                 [MethodImpl(MethodImplOptions.AggressiveInlining)]
                 get
                 {
-                    return ioPendingRequests.Count == 0
-                        && retryRequests.Count == 0;
+                    return SyncIoPendingCount == 0 && retryRequests.Count == 0;
                 }
             }
 

cs/src/core/Index/FASTER/FASTERThread.cs

@@ -279,7 +279,7 @@ internal void InternalCompletePendingRequests(FasterExecutionContext opCtx, Fast
 
         internal async ValueTask InternalCompletePendingRequestsAsync(FasterExecutionContext opCtx, FasterExecutionContext currentCtx, ClientSession<Key, Value, Input, Output, Context, Functions> clientSession, CancellationToken token = default)
         {
-            while (opCtx.ioPendingRequests.Count > 0)
+            while (opCtx.SyncIoPendingCount > 0)
             {
                 AsyncIOContext<Key, Value> request;
 
@@ -363,7 +363,7 @@ internal void InternalCompletePendingRequest(FasterExecutionContext opCtx, Faste
             }
         }
 
-        internal (Status, Output) InternalCompletePendingReadRequestAsync(FasterExecutionContext opCtx, FasterExecutionContext currentCtx, AsyncIOContext<Key, Value> request, PendingContext pendingContext)
+        internal (Status, Output) InternalCompletePendingReadRequest(FasterExecutionContext opCtx, FasterExecutionContext currentCtx, AsyncIOContext<Key, Value> request, PendingContext pendingContext)
         {
             (Status, Output) s = default;
 

cs/src/core/Utilities/AsyncQueue.cs

@@ -58,6 +58,16 @@ public async Task<T> DequeueAsync(CancellationToken cancellationToken = default)
             }
         }
 
+        /// <summary>
+        /// Wait for queue to have at least one entry
+        /// </summary>
+        /// <param name="token"></param>
+        /// <returns></returns>
+        public async Task WaitForEntryAsync(CancellationToken token = default)
+        {
+            await semaphore.WaitAsync(token);
+        }
+
         /// <summary>
         /// Try dequeue (if item exists)
         /// </summary>