finished ch15.6 and ch15

.obsidian/workspace.json

@@ -35,6 +35,34 @@
               "title": "Smart Pointers"
             }
           },
+          {
+            "id": "feca3744741d15fc",
+            "type": "leaf",
+            "state": {
+              "type": "markdown",
+              "state": {
+                "file": "Concurrency.md",
+                "mode": "source",
+                "source": false
+              },
+              "icon": "lucide-file",
+              "title": "Concurrency"
+            }
+          },
+          {
+            "id": "b104e4647c0ac328",
+            "type": "leaf",
+            "state": {
+              "type": "markdown",
+              "state": {
+                "file": "Leaky Reference Cycles.md",
+                "mode": "source",
+                "source": false
+              },
+              "icon": "lucide-file",
+              "title": "Leaky Reference Cycles"
+            }
+          },
           {
             "id": "74da570aae42b3e7",
             "type": "leaf",
@@ -74,7 +102,7 @@
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           }
         ],
-        "currentTab": 4
+        "currentTab": 2
       }
     ],
     "direction": "vertical"
@@ -217,11 +245,13 @@
       "command-palette:Open command palette": false
     }
   },
-  "active": "6ed9f182aa3d5f3e",
+  "active": "feca3744741d15fc",
   "lastOpenFiles": [
-    "Ref Cell Mutability.md",
     "Smart Pointers.md",
+    "Concurrency.md",
+    "Leaky Reference Cycles.md",
     "Test Controls.md",
+    "Ref Cell Mutability.md",
     "Reference Counter Smart Pointer.md",
     "The Performance Closures and Iterators.md",
     "Improving The IO Project.md",
@@ -244,8 +274,6 @@
     "Constants.md",
     "Crates.md",
     "Data Types.md",
-    "Enums.md",
-    "Error Handling.md",
     "does_not_compile.svg",
     "Untitled.canvas",
     "Good and Bad Code/Commenting Pratices",