[base] Template MatchFun in TemplateHashMapImpl

src/base/hashmap.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // The reason we write our own hash map instead of using unordered_map in STL,
 // is that STL containers use a mutex pool on debug build, which will lead to
 // deadlock when we are using async signal handler.
 
 #ifndef V8_BASE_HASHMAP_H_
 #define V8_BASE_HASHMAP_H_
 
 #include <stdlib.h>
 
 #include "src/base/bits.h"
 #include "src/base/hashmap-entry.h"
 #include "src/base/logging.h"
 
 namespace v8 {
 namespace base {
 
 class DefaultAllocationPolicy {
  public:
   V8_INLINE void* New(size_t size) { return malloc(size); }
   V8_INLINE static void Delete(void* p) { free(p); }
 };
 
-// Metaprogramming helper to allow pointer keys to be passed by value and
-// non-pointer keys by const reference.
-template <typename Key>
-struct MatchFunHelper;
-
-template <typename Key, typename Value, class AllocationPolicy>
+template <typename Key, typename Value, class MatchFun, class AllocationPolicy>
 class TemplateHashMapImpl {
  public:
-  typedef typename MatchFunHelper<Key>::Fun MatchFun;
   typedef TemplateHashMapEntry<Key, Value> Entry;
 
   // The default capacity.  This is used by the call sites which want
   // to pass in a non-default AllocationPolicy but want to use the
   // default value of capacity specified by the implementation.
   static const uint32_t kDefaultHashMapCapacity = 8;
 
   // initial_capacity is the size of the initial hash map;
   // it must be a power of 2 (and thus must not be 0).
-  TemplateHashMapImpl(MatchFun match,
+  TemplateHashMapImpl(MatchFun match = MatchFun(),
                       uint32_t capacity = kDefaultHashMapCapacity,
                       AllocationPolicy allocator = AllocationPolicy());
 
   ~TemplateHashMapImpl();
 
   // If an entry with matching key is found, returns that entry.
   // Otherwise, nullptr is returned.
   Entry* Lookup(const Key& key, uint32_t hash) const;
 
   // If an entry with matching key is found, returns that entry.
@@ skipping 23 matching lines @@
   //
   // for (Entry* p = map.Start(); p != nullptr; p = map.Next(p)) {
   //   ...
   // }
   //
   // If entries are inserted during iteration, the effect of
   // calling Next() is undefined.
   Entry* Start() const;
   Entry* Next(Entry* entry) const;
 
-  // Some match functions defined for convenience.
-  // TODO(leszeks): This isn't really matching pointers, so the name doesn't
-  // really make sense, but we should remove this entirely and template the map
-  // on the matching function.
-  static bool PointersMatch(typename MatchFunHelper<Key>::KeyRef key1,
-                            typename MatchFunHelper<Key>::KeyRef key2) {
-    return key1 == key2;
-  }
-
  private:
-  MatchFun match_;
   Entry* map_;
   uint32_t capacity_;
   uint32_t occupancy_;
+  MatchFun match_;
   AllocationPolicy allocator_;
 
   Entry* map_end() const { return map_ + capacity_; }
   Entry* Probe(const Key& key, uint32_t hash) const;
   Entry* FillEmptyEntry(Entry* entry, const Key& key, const Value& value,
                         uint32_t hash);
   void Initialize(uint32_t capacity);
   void Resize();
 };
 
-template <typename Key>
-struct MatchFunHelper {
-  typedef const Key& KeyRef;
-  typedef bool (*Fun)(KeyRef key1, KeyRef key2);
-};
-
-template <typename Key>
-struct MatchFunHelper<Key*> {
-  typedef Key* KeyRef;
-  typedef bool (*Fun)(KeyRef key1, KeyRef key2);
-};
-
-typedef TemplateHashMapImpl<void*, void*, DefaultAllocationPolicy> HashMap;
-
-template <typename Key, typename Value, class AllocationPolicy>
-TemplateHashMapImpl<Key, Value, AllocationPolicy>::TemplateHashMapImpl(
-    MatchFun match, uint32_t initial_capacity, AllocationPolicy allocator)
-    : allocator_(allocator) {
-  match_ = match;
+template <typename Key, typename Value, typename MatchFun,
+          class AllocationPolicy>
+TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::
+    TemplateHashMapImpl(MatchFun match, uint32_t initial_capacity,
+                        AllocationPolicy allocator)
+    : match_(match), allocator_(allocator) {
   Initialize(initial_capacity);
 }
 
-template <typename Key, typename Value, class AllocationPolicy>
-TemplateHashMapImpl<Key, Value, AllocationPolicy>::~TemplateHashMapImpl() {
+template <typename Key, typename Value, typename MatchFun,
+          class AllocationPolicy>
+TemplateHashMapImpl<Key, Value, MatchFun,
+                    AllocationPolicy>::~TemplateHashMapImpl() {
   allocator_.Delete(map_);
 }
 
-template <typename Key, typename Value, class AllocationPolicy>
-typename TemplateHashMapImpl<Key, Value, AllocationPolicy>::Entry*
-TemplateHashMapImpl<Key, Value, AllocationPolicy>::Lookup(const Key& key,
-                                                          uint32_t hash) const {
+template <typename Key, typename Value, typename MatchFun,
+          class AllocationPolicy>
+typename TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::Entry*
+TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::Lookup(
+    const Key& key, uint32_t hash) const {
   Entry* entry = Probe(key, hash);
   return entry->exists() ? entry : nullptr;
 }
 
-template <typename Key, typename Value, class AllocationPolicy>
-typename TemplateHashMapImpl<Key, Value, AllocationPolicy>::Entry*
-TemplateHashMapImpl<Key, Value, AllocationPolicy>::LookupOrInsert(
+template <typename Key, typename Value, typename MatchFun,
+          class AllocationPolicy>
+typename TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::Entry*
+TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::LookupOrInsert(
     const Key& key, uint32_t hash) {
   // Find a matching entry.
   Entry* entry = Probe(key, hash);
   if (entry->exists()) {
     return entry;
   }
 
   return FillEmptyEntry(entry, key, Value(), hash);
 }
 
-template <typename Key, typename Value, class AllocationPolicy>
-typename TemplateHashMapImpl<Key, Value, AllocationPolicy>::Entry*
-TemplateHashMapImpl<Key, Value, AllocationPolicy>::InsertNew(const Key& key,
-                                                             uint32_t hash) {
+template <typename Key, typename Value, typename MatchFun,
+          class AllocationPolicy>
+typename TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::Entry*
+TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::InsertNew(
+    const Key& key, uint32_t hash) {
   Entry* entry = Probe(key, hash);
   return FillEmptyEntry(entry, key, Value(), hash);
 }
 
-template <typename Key, typename Value, class AllocationPolicy>
-Value TemplateHashMapImpl<Key, Value, AllocationPolicy>::Remove(const Key& key,
-                                                                uint32_t hash) {
+template <typename Key, typename Value, typename MatchFun,
+          class AllocationPolicy>
+Value TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::Remove(
+    const Key& key, uint32_t hash) {
   // Lookup the entry for the key to remove.
   Entry* p = Probe(key, hash);
   if (!p->exists()) {
     // Key not found nothing to remove.
     return nullptr;
   }
 
   Value value = p->value;
   // To remove an entry we need to ensure that it does not create an empty
   // entry that will cause the search for another entry to stop too soon. If all
@@ skipping 38 matching lines @@
       p = q;
     }
   }
 
   // Clear the entry which is allowed to en emptied.
   p->clear();
   occupancy_--;
   return value;
 }
 
-template <typename Key, typename Value, class AllocationPolicy>
-void TemplateHashMapImpl<Key, Value, AllocationPolicy>::Clear() {
+template <typename Key, typename Value, typename MatchFun,
+          class AllocationPolicy>
+void TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::Clear() {
   // Mark all entries as empty.
   const Entry* end = map_end();
   for (Entry* entry = map_; entry < end; entry++) {
     entry->clear();
   }
   occupancy_ = 0;
 }
 
-template <typename Key, typename Value, class AllocationPolicy>
-typename TemplateHashMapImpl<Key, Value, AllocationPolicy>::Entry*
-TemplateHashMapImpl<Key, Value, AllocationPolicy>::Start() const {
+template <typename Key, typename Value, typename MatchFun,
+          class AllocationPolicy>
+typename TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::Entry*
+TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::Start() const {
   return Next(map_ - 1);
 }
 
-template <typename Key, typename Value, class AllocationPolicy>
-typename TemplateHashMapImpl<Key, Value, AllocationPolicy>::Entry*
-TemplateHashMapImpl<Key, Value, AllocationPolicy>::Next(Entry* entry) const {
+template <typename Key, typename Value, typename MatchFun,
+          class AllocationPolicy>
+typename TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::Entry*
+TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::Next(
+    Entry* entry) const {
   const Entry* end = map_end();
   DCHECK(map_ - 1 <= entry && entry < end);
   for (entry++; entry < end; entry++) {
     if (entry->exists()) {
       return entry;
     }
   }
   return nullptr;
 }
 
-template <typename Key, typename Value, class AllocationPolicy>
-typename TemplateHashMapImpl<Key, Value, AllocationPolicy>::Entry*
-TemplateHashMapImpl<Key, Value, AllocationPolicy>::Probe(const Key& key,
-                                                         uint32_t hash) const {
+template <typename Key, typename Value, typename MatchFun,
+          class AllocationPolicy>
+typename TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::Entry*
+TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::Probe(
+    const Key& key, uint32_t hash) const {
   DCHECK(base::bits::IsPowerOfTwo32(capacity_));
   Entry* entry = map_ + (hash & (capacity_ - 1));
   const Entry* end = map_end();
   DCHECK(map_ <= entry && entry < end);
 
   DCHECK(occupancy_ < capacity_);  // Guarantees loop termination.
   while (entry->exists() && (hash != entry->hash || !match_(key, entry->key))) {
     entry++;
     if (entry >= end) {
       entry = map_;
     }
   }
 
   return entry;
 }
 
-template <typename Key, typename Value, class AllocationPolicy>
-typename TemplateHashMapImpl<Key, Value, AllocationPolicy>::Entry*
-TemplateHashMapImpl<Key, Value, AllocationPolicy>::FillEmptyEntry(
+template <typename Key, typename Value, typename MatchFun,
+          class AllocationPolicy>
+typename TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::Entry*
+TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::FillEmptyEntry(
     Entry* entry, const Key& key, const Value& value, uint32_t hash) {
   DCHECK(!entry->exists());
 
   new (entry) Entry(key, value, hash);
   occupancy_++;
 
   // Grow the map if we reached >= 80% occupancy.
   if (occupancy_ + occupancy_ / 4 >= capacity_) {
     Resize();
     entry = Probe(key, hash);
   }
 
   return entry;
 }
 
-template <typename Key, typename Value, class AllocationPolicy>
-void TemplateHashMapImpl<Key, Value, AllocationPolicy>::Initialize(
+template <typename Key, typename Value, typename MatchFun,
+          class AllocationPolicy>
+void TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::Initialize(
     uint32_t capacity) {
   DCHECK(base::bits::IsPowerOfTwo32(capacity));
   map_ = reinterpret_cast<Entry*>(allocator_.New(capacity * sizeof(Entry)));
   if (map_ == nullptr) {
     FATAL("Out of memory: HashMap::Initialize");
     return;
   }
   capacity_ = capacity;
   Clear();
 }
 
-template <typename Key, typename Value, class AllocationPolicy>
-void TemplateHashMapImpl<Key, Value, AllocationPolicy>::Resize() {
+template <typename Key, typename Value, typename MatchFun,
+          class AllocationPolicy>
+void TemplateHashMapImpl<Key, Value, MatchFun, AllocationPolicy>::Resize() {
   Entry* map = map_;
   uint32_t n = occupancy_;
 
   // Allocate larger map.
   Initialize(capacity_ * 2);
 
   // Rehash all current entries.
   for (Entry* entry = map; n > 0; entry++) {
     if (entry->exists()) {
       Entry* new_entry = Probe(entry->key, entry->hash);
       new_entry =
           FillEmptyEntry(new_entry, entry->key, entry->value, entry->hash);
       n--;
     }
   }
 
   // Delete old map.
   allocator_.Delete(map);
 }
 
+template <typename AllocationPolicy>
+class PointerTemplateHashMapImpl
+    : public TemplateHashMapImpl<void*, void*, bool (*)(void*, void*),
+                                 AllocationPolicy> {
+  typedef TemplateHashMapImpl<void*, void*, bool (*)(void*, void*),
+                              AllocationPolicy>
+      Base;

[rmcilroy, 2016/09/20 16:06:03]

weird formating here - I guess this was git cl format. Any way you can wrangle
it into submission? (no worries if not).

[Leszek Swirski, 2016/09/26 16:54:52]

Not really, I could define the MatchFun typedef higher to do it but I don't want
Base to be public, so there'd be some weird interleaving of visibility modifiers
in that case.

+
+ public:
+  typedef bool (*MatchFun)(void*, void*);
+
+  PointerTemplateHashMapImpl(MatchFun match = PointersMatch,
+                             uint32_t capacity = Base::kDefaultHashMapCapacity,
+                             AllocationPolicy allocator = AllocationPolicy())
+      : Base(match, capacity, allocator) {}
+
+  static bool PointersMatch(void* key1, void* key2) { return key1 == key2; }
+};
+
+typedef PointerTemplateHashMapImpl<DefaultAllocationPolicy> HashMap;
+
 // A hash map for pointer keys and values with an STL-like interface.
 template <class Key, class Value, class AllocationPolicy>
-class TemplateHashMap
-    : private TemplateHashMapImpl<void*, void*, AllocationPolicy> {
+class TemplateHashMap : private PointerTemplateHashMapImpl<AllocationPolicy> {
+  typedef PointerTemplateHashMapImpl<AllocationPolicy> Base;
+
  public:
+  typedef bool (*MatchFun)(void*, void*);
+
   STATIC_ASSERT(sizeof(Key*) == sizeof(void*));    // NOLINT
   STATIC_ASSERT(sizeof(Value*) == sizeof(void*));  // NOLINT
   struct value_type {
     Key* first;
     Value* second;
   };
 
   class Iterator {
    public:
     Iterator& operator++() {
       entry_ = map_->Next(entry_);
       return *this;
     }
 
     value_type* operator->() { return reinterpret_cast<value_type*>(entry_); }
     bool operator!=(const Iterator& other) { return entry_ != other.entry_; }
 
    private:
-    Iterator(const TemplateHashMapImpl<void*, void*, AllocationPolicy>* map,
-             typename TemplateHashMapImpl<void*, void*,
-                                          AllocationPolicy>::Entry* entry)
+    Iterator(const Base* map, typename Base::Entry* entry)
         : map_(map), entry_(entry) {}
 
-    const TemplateHashMapImpl<void*, void*, AllocationPolicy>* map_;
-    typename TemplateHashMapImpl<void*, void*, AllocationPolicy>::Entry* entry_;
+    const Base* map_;
+    typename Base::Entry* entry_;
 
     friend class TemplateHashMap;
   };
 
-  TemplateHashMap(typename TemplateHashMapImpl<
-                      void*, void*, AllocationPolicy>::MatchFun match,
+  TemplateHashMap(MatchFun match,
                   AllocationPolicy allocator = AllocationPolicy())
-      : TemplateHashMapImpl<void*, void*, AllocationPolicy>(
-            match,
-            TemplateHashMapImpl<void*, void*,
-                                AllocationPolicy>::kDefaultHashMapCapacity,
-            allocator) {}
+      : Base(match, Base::kDefaultHashMapCapacity, allocator) {}
 
   Iterator begin() const { return Iterator(this, this->Start()); }
   Iterator end() const { return Iterator(this, nullptr); }
   Iterator find(Key* key, bool insert = false) {
     if (insert) {
       return Iterator(this, this->LookupOrInsert(key, key->Hash()));
     }
     return Iterator(this, this->Lookup(key, key->Hash()));
   }
 };
 
 }  // namespace base
 }  // namespace v8
 
 #endif  // V8_BASE_HASHMAP_H_