Revert "Revert "Fix dlsym(3) to do breadth first search.""

This reverts commit 1b1966d944.

Change-Id: I05d6d3481aaf8f3e260d2e5e950248519a1d347f

linker/linked_list.h

@@ -31,13 +31,45 @@ struct LinkedListEntry {
 template<typename T, typename Allocator>
 class LinkedList {
  public:
-  LinkedList() : head_(nullptr) {}
+  LinkedList() : head_(nullptr), tail_(nullptr) {}
 
   void push_front(T* const element) {
     LinkedListEntry<T>* new_entry = Allocator::alloc();
     new_entry->next = head_;
     new_entry->element = element;
     head_ = new_entry;
+    if (tail_ == nullptr) {
+      tail_ = new_entry;
+    }
+  }
+
+  void push_back(T* const element) {
+    LinkedListEntry<T>* new_entry = Allocator::alloc();
+    new_entry->next = nullptr;
+    new_entry->element = element;
+    if (tail_ == nullptr) {
+      tail_ = head_ = new_entry;
+    } else {
+      tail_->next = new_entry;
+      tail_ = new_entry;
+    }
+  }
+
+  T* pop_front() {
+    if (head_ == nullptr) {
+      return nullptr;
+    }
+
+    LinkedListEntry<T>* entry = head_;
+    T* element = entry->element;
+    head_ = entry->next;
+    Allocator::free(entry);
+
+    if (head_ == nullptr) {
+      tail_ = nullptr;
+    }
+
+    return element;
   }
 
   void clear() {
@@ -46,6 +78,8 @@ class LinkedList {
       head_ = head_->next;
       Allocator::free(p);
     }
+
+    tail_ = nullptr;
   }
 
   template<typename F>
@@ -68,6 +102,7 @@ class LinkedList {
 
  private:
   LinkedListEntry<T>* head_;
+  LinkedListEntry<T>* tail_;
   DISALLOW_COPY_AND_ASSIGN(LinkedList);
 };