Writeables revised

Read-ahead for DataStream Processing

Src/Myc.Trade.DataStream.pas

@@ -101,7 +101,8 @@ type
         // Used by cache to actually load an uncached file.
         function DoLoad(const FileName: string): TFuture<TArray<TDataPoint<T>>>;
 
-        function LoadFile(DataFile: TAuraDataFile; Terminated: TState; Proc: TDataProc<T>): TState;
+        function ProcessFile(FileInfo: TAuraDataFile; const DataFile: TFuture<TArray<TDataPoint<T>>>; Terminated: TState; Proc: TDataProc<T>):
+            TState;
 
     strict private
         class var
@@ -392,27 +393,35 @@ begin
 
     Result :=
         FindFirstFile(Symbol)
-            .Chain(function(const FirstFile: TAuraDataFile): TState begin Result := LoadFile(FirstFile, terminated, capProc); end);
+            .Chain(
+            function(const FirstFileInfo: TAuraDataFile): TState
+            begin
+                Result := ProcessFile(FirstFileInfo, LoadDataFile(FirstFileInfo), terminated, capProc);
+            end);
 end;
 
 function TAuraDataServer<T>.LoadDataFile(const DataFile: TAuraDataFile): TFuture<TArray<TDataPoint<T>>>;
 begin
-    Result := FCachedFiles.GetOrAdd(DataFile.GetFullFileName);
+    if DataFile.IsValid then
+        Result := FCachedFiles.GetOrAdd(DataFile.GetFullFileName);
 end;
 
-function TAuraDataServer<T>.LoadFile(DataFile: TAuraDataFile; Terminated: TState; Proc: TDataProc<T>): TState;
+function TAuraDataServer<T>.ProcessFile(FileInfo: TAuraDataFile; const DataFile: TFuture<TArray<TDataPoint<T>>>; Terminated: TState; Proc:
+    TDataProc<T>): TState;
 begin
-    if not DataFile.IsValid or Terminated.IsSet then
+    if not FileInfo.IsValid or Terminated.IsSet then
         exit(TState.Null);
 
-    var data := FCachedFiles.GetOrAdd(DataFile.GetFullFileName);
+    // Read ahead the next file, while processing the current one
+    var nextFileInfo := FileInfo.GetNextFile;
+    var nextFile := LoadDataFile( nextFileInfo );
 
     Result :=
-        data.Chain(
+        DataFile.Chain(
             function(const Data: TArray<TDataPoint<T>>): TState
             begin
                 Proc(Data, Terminated);
-                Result := LoadFile(DataFile.GetNextFile, Terminated, Proc);
+                Result := ProcessFile(nextFileInfo, nextFile, Terminated, Proc);
             end
         );
 end;