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Minimal test - lines (54, 122)

Code

class nsCategoryCache final {
 public:
  explicit nsCategoryCache(const char* aCategory) : mCategoryName(aCategory) {
    MOZ_ASSERT(NS_IsMainThread());
  }
  ~nsCategoryCache() {
    MOZ_ASSERT(NS_IsMainThread());
    if (mObserver) {
      mObserver->ListenerDied();
    }
  }

  void GetEntries(nsCOMArray& aResult) {
    MOZ_ASSERT(NS_IsMainThread());
    LazyInit();

    AddEntries(aResult);
  }

  /**
   * This function returns an nsCOMArray of interface pointers to the cached
   * category enries for the requested category.  This was added in order to be
   * used in call sites where the overhead of excessive allocations can be
   * unacceptable.  See bug 1360971 for an example.
   */
  const nsCOMArray& GetCachedEntries() {
    MOZ_ASSERT(NS_IsMainThread());
    LazyInit();

    if (mCachedEntries.IsEmpty()) {
      AddEntries(mCachedEntries);
    }
    return mCachedEntries;
  }

 private:
  void LazyInit() {
    // Lazy initialization, so that services in this category can't
    // cause reentrant getService (bug 386376)
    if (!mObserver) {
      mObserver = new nsCategoryObserver(mCategoryName);
      mObserver->SetListener(nsCategoryCache::OnCategoryChanged, this);
    }
  }

  void AddEntries(nsCOMArray& aResult) {
    for (auto iter = mObserver->GetHash().Iter(); !iter.Done(); iter.Next()) {
      nsISupports* entry = iter.UserData();
      nsCOMPtr service = do_QueryInterface(entry);
      if (service) {
        aResult.AppendElement(service.forget());
      }
    }
  }

  static void OnCategoryChanged(void* aClosure) {
    MOZ_ASSERT(NS_IsMainThread());
    auto self = static_cast*>(aClosure);
    self->mCachedEntries.Clear();
  }

 private:
  // Not to be implemented
  nsCategoryCache(const nsCategoryCache&);

  nsCString mCategoryName;
  RefPtr mObserver;
  nsCOMArray mCachedEntries;
};

Minimal test - lines (22, 44)

Code

class nsCategoryObserver final : public nsIObserver {
  ~nsCategoryObserver();

 public:
  explicit nsCategoryObserver(const nsACString& aCategory);

  void ListenerDied();
  void SetListener(void(aCallback)(void*), void* aClosure);
  nsInterfaceHashtable& GetHash() {
    return mHash;
  }

  NS_DECL_ISUPPORTS
  NS_DECL_NSIOBSERVER
 private:
  void RemoveObservers();

  nsInterfaceHashtable mHash;
  nsCString mCategory;
  void (*mCallback)(void*);
  void* mClosure;
  bool mObserversRemoved;
};