From 15b7df0982927469acbafec1cfc2a64769d4929b Mon Sep 17 00:00:00 2001
From: ShikiSuen <shikisuen@outlook.com>
Date: Thu, 2 Mar 2023 20:27:59 +0800
Subject: [PATCH] Fix memory leak with Vertex. (#96)

---
 Sources/Megrez/2_Walker.swift | 14 +++++++++++---
 Sources/Megrez/5_Vertex.swift | 12 +++++++++++-
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/Sources/Megrez/2_Walker.swift b/Sources/Megrez/2_Walker.swift
index bc34c60..8553fdd 100644
--- a/Sources/Megrez/2_Walker.swift
+++ b/Sources/Megrez/2_Walker.swift
@@ -32,6 +32,7 @@ public extension Megrez.Compositor {
     }
 
     let terminal = Vertex(node: .init(keyArray: ["_TERMINAL_"]))
+    var root = Vertex(node: .init(keyArray: ["_ROOT_"]))
 
     for (i, vertexSpan) in vertexSpans.enumerated() {
       for vertex in vertexSpan {
@@ -46,11 +47,10 @@ public extension Megrez.Compositor {
       }
     }
 
-    let root = Vertex(node: .init(keyArray: ["_ROOT_"]))
     root.distance = 0
     root.edges.append(contentsOf: vertexSpans[0])
 
-    var ordered: [Vertex] = topologicalSort(root: root)
+    var ordered = topologicalSort(root: &root)
     for (j, neta) in ordered.reversed().enumerated() {
       for (k, _) in neta.edges.enumerated() {
         relax(u: neta, v: &neta.edges[k])
@@ -58,15 +58,23 @@ public extension Megrez.Compositor {
       ordered[j] = neta
     }
 
+    var iterated = terminal
     var walked = [Node]()
     var totalLengthOfKeys = 0
-    var iterated = terminal
+
     while let itPrev = iterated.prev {
       walked.append(itPrev.node)
       iterated = itPrev
       totalLengthOfKeys += iterated.node.spanLength
     }
 
+    // 清理內容，否則會有記憶體洩漏。
+    ordered.removeAll()
+    vertexSpans.removeAll()
+    iterated.destroy()
+    root.destroy()
+    terminal.destroy()
+
     guard totalLengthOfKeys == keys.count else {
       print("!!! ERROR A")
       return (result, false)
diff --git a/Sources/Megrez/5_Vertex.swift b/Sources/Megrez/5_Vertex.swift
index 3a64b31..6072d33 100644
--- a/Sources/Megrez/5_Vertex.swift
+++ b/Sources/Megrez/5_Vertex.swift
@@ -29,6 +29,16 @@ extension Megrez.Compositor {
     public init(node: Node) {
       self.node = node
     }
+
+    /// 讓一個 Vertex 順藤摸瓜地將自己的所有的連帶的 Vertex 都摧毀，再摧毀自己。
+    /// 此過程必須在一套 Vertex 全部使用完畢之後執行一次，可防止記憶體洩漏。
+    public func destroy() {
+      while prev?.prev != nil { prev?.destroy() }
+      prev = nil
+      edges.forEach { $0.destroy() }
+      edges.removeAll()
+      node = .init()
+    }
   }
 
   /// 卸勁函式。
@@ -67,7 +77,7 @@ extension Megrez.Compositor {
   /// 至於其遞迴版本，則類似於 Cormen 在 2001 年的著作「Introduction to Algorithms」當中的樣子。
   /// - Parameter root: 根頂點。
   /// - Returns: 排序結果（頂點陣列）。
-  func topologicalSort(root: Vertex) -> [Vertex] {
+  func topologicalSort(root: inout Vertex) -> [Vertex] {
     class State {
       var iterIndex: Int
       let vertex: Vertex