Fix the symbol cache and image cache

PortfolioManager/Cache/ImageCache.cs

@@ -57,6 +57,7 @@ namespace PortfolioManager.Cache
     {
       lock (thisLock)
       {
+        DisposeBitmaps();
         imageCache = new Dictionary<ImageType, Bitmap>();
       }
     }
@@ -66,22 +67,30 @@ namespace PortfolioManager.Cache
       lock (thisLock)
       {
         if (null == imageCacheInstance) return;
-        List<Bitmap> bitmaps = imageCache.Values.ToList();
-        foreach (Bitmap bitmap in bitmaps)
-        {
-          bitmap.Dispose();
-        }
+        DisposeBitmaps();
         imageCache = null;
         imageCacheInstance = null;
       }
     }
-
-    public IImage GetImage(ImageCache.ImageType imageType)
+    
+    private void DisposeBitmaps()
     {
-      lock(this)
+      if(null == imageCache)return;
+      List<Bitmap> bitmaps = imageCache.Values.ToList();
+      foreach (Bitmap bitmap in bitmaps)
       {
-        return imageCache[imageType];
+        bitmap.Dispose();
       }
     }
+
+    public IImage GetImage(ImageType imageType)
+    {
+        lock(thisLock)
+        {
+          if (imageCache == null)throw new ObjectDisposedException(nameof(ImageCache));
+          if (!imageCache.TryGetValue(imageType, out var bitmap))throw new KeyNotFoundException($"Image {imageType} not found in cache.");
+          return bitmap;
+        }
+    }    
   }
 }

PortfolioManager/Cache/SymbolCache.cs

@@ -10,7 +10,8 @@ namespace PortfolioManager.Cache
   public class SymbolCache : IDisposable
   {
     private List<String> symbolCache=new List<String>();
-    private Object thisLock=new Object();
+    private readonly Object thisLock=new Object();
+    private readonly Object fetchLock = new Object();
     private Thread cacheMonitorThread=null;
     private volatile bool threadRun=true;
     private int cacheRefreshAfter=60000;        // Invalidate cache after
@@ -60,12 +61,15 @@ namespace PortfolioManager.Cache
       {
         if(symbolCache.Count>0)return new List<string>(symbolCache);
       }
-      List<String> symbols = PricingDA.GetSymbols();
-      lock(thisLock)
+      lock(fetchLock)
       {
-        if(symbolCache.Count>0)return new List<string>(symbolCache);
-        symbolCache=new List<String>(symbols);
-        return new List<string>(symbols);
+        List<String> symbols = PricingDA.GetSymbols();
+        lock(thisLock)
+        {
+          if(symbolCache.Count>0)return new List<string>(symbolCache);
+          symbolCache=new List<String>(symbols);
+          return new List<string>(symbols);
+        }
       }
     }
 
@@ -81,7 +85,7 @@ namespace PortfolioManager.Cache
         if(quantums>cacheRefreshAfter)
         {
           quantums=0;
-          List<String> symbols =  PricingDA.GetSymbols();
+          List<String> symbols = PricingDA.GetSymbols();
           lock(thisLock)
           {
             symbolCache=new List<string>(symbols);
@@ -90,4 +94,4 @@ namespace PortfolioManager.Cache
       }
     }
   }
-}
+}