refactor constructor of LRUCacheShard

Summary:
Update LRUCacheShard constructor so that adding new params to it don't need to add extra SetXXX() methods.
Closes https://github.com/facebook/rocksdb/pull/3896

Differential Revision: D8128618

Pulled By: yiwu-arbug

fbshipit-source-id: 6afa715de1493a50de413678761a765e3af9b83b

cache/lru_cache.cc

@@ -99,14 +99,20 @@ void LRUHandleTable::Resize() {
   length_ = new_length;
 }
 
-LRUCacheShard::LRUCacheShard()
-    : capacity_(0), high_pri_pool_usage_(0), strict_capacity_limit_(false),
-      high_pri_pool_ratio_(0), high_pri_pool_capacity_(0), usage_(0),
+LRUCacheShard::LRUCacheShard(size_t capacity, bool strict_capacity_limit,
+                             double high_pri_pool_ratio)
+    : capacity_(0),
+      high_pri_pool_usage_(0),
+      strict_capacity_limit_(strict_capacity_limit),
+      high_pri_pool_ratio_(high_pri_pool_ratio),
+      high_pri_pool_capacity_(0),
+      usage_(0),
       lru_usage_(0) {
   // Make empty circular linked list
   lru_.next = &lru_;
   lru_.prev = &lru_;
   lru_low_pri_ = &lru_;
+  SetCapacity(capacity);
 }
 
 LRUCacheShard::~LRUCacheShard() {}
@@ -244,17 +250,13 @@ void* LRUCacheShard::operator new(size_t size) {
   return port::cacheline_aligned_alloc(size);
 }
 
-void* LRUCacheShard::operator new[](size_t size) {
-  return port::cacheline_aligned_alloc(size);
-}
+void* LRUCacheShard::operator new(size_t /*size*/, void* ptr) { return ptr; }
 
 void LRUCacheShard::operator delete(void *memblock) {
   port::cacheline_aligned_free(memblock);
 }
 
-void LRUCacheShard::operator delete[](void* memblock) {
-  port::cacheline_aligned_free(memblock);
-}
+void LRUCacheShard::operator delete(void* /*memblock*/, void* /*ptr*/) {}
 
 void LRUCacheShard::SetCapacity(size_t capacity) {
   autovector<LRUHandle*> last_reference_list;
@@ -473,15 +475,21 @@ LRUCache::LRUCache(size_t capacity, int num_shard_bits,
                    bool strict_capacity_limit, double high_pri_pool_ratio)
     : ShardedCache(capacity, num_shard_bits, strict_capacity_limit) {
   num_shards_ = 1 << num_shard_bits;
-  shards_ = new LRUCacheShard[num_shards_];
-  SetCapacity(capacity);
-  SetStrictCapacityLimit(strict_capacity_limit);
+  shards_ = reinterpret_cast<LRUCacheShard*>(
+      port::cacheline_aligned_alloc(sizeof(LRUCacheShard) * num_shards_));
+  size_t per_shard = (capacity + (num_shards_ - 1)) / num_shards_;
   for (int i = 0; i < num_shards_; i++) {
-    shards_[i].SetHighPriorityPoolRatio(high_pri_pool_ratio);
+    new (&shards_[i])
+        LRUCacheShard(per_shard, strict_capacity_limit, high_pri_pool_ratio);
   }
 }
 
-LRUCache::~LRUCache() { delete[] shards_; }
+LRUCache::~LRUCache() {
+  for (int i = 0; i < num_shards_; i++) {
+    shards_[i].~LRUCacheShard();
+  }
+  port::cacheline_aligned_free(shards_);
+}
 
 CacheShard* LRUCache::GetShard(int shard) {
   return reinterpret_cast<CacheShard*>(&shards_[shard]);

cache/lru_cache.h

@@ -156,7 +156,8 @@ class LRUHandleTable {
 // A single shard of sharded cache.
 class ALIGN_AS(CACHE_LINE_SIZE) LRUCacheShard : public CacheShard {
  public:
-  LRUCacheShard();
+  LRUCacheShard(size_t capacity, bool strict_capacity_limit,
+                double high_pri_pool_ratio);
   virtual ~LRUCacheShard();
 
   // Separate from constructor so caller can easily make an array of LRUCache
@@ -206,13 +207,16 @@ class ALIGN_AS(CACHE_LINE_SIZE) LRUCacheShard : public CacheShard {
   double GetHighPriPoolRatio();
 
   // Overloading to aligned it to cache line size
+  // They are used by tests.
   void* operator new(size_t);
 
-  void* operator new[](size_t);
+  // placement new
+  void* operator new(size_t, void*);
 
   void operator delete(void *);
 
-  void operator delete[](void*);
+  // placement delete, does nothing.
+  void operator delete(void*, void*);
 
  private:
   void LRU_Remove(LRUHandle* e);

cache/lru_cache_test.cc

@@ -7,6 +7,7 @@
 
 #include <string>
 #include <vector>
+#include "port/port.h"
 #include "util/testharness.h"
 
 namespace rocksdb {
@@ -17,19 +18,8 @@ class LRUCacheTest : public testing::Test {
   ~LRUCacheTest() {}
 
   void NewCache(size_t capacity, double high_pri_pool_ratio = 0.0) {
-    cache_.reset(
-#if defined(_MSC_VER)
-#pragma warning(push)
-#pragma warning(disable: 4316) // We've validated the alignment with the new operators
-#endif
-      new LRUCacheShard()
-#if defined(_MSC_VER)
-#pragma warning(pop)
-#endif
-    );
-    cache_->SetCapacity(capacity);
-    cache_->SetStrictCapacityLimit(false);
-    cache_->SetHighPriorityPoolRatio(high_pri_pool_ratio);
+    cache_.reset(new LRUCacheShard(capacity, false /*strict_capcity_limit*/,
+                                   high_pri_pool_ratio));
   }
 
   void Insert(const std::string& key,
@@ -114,7 +104,7 @@ TEST_F(LRUCacheTest, BasicLRU) {
   ValidateLRUList({"e", "z", "d", "u", "v"});
 }
 
-TEST_F(LRUCacheTest, MidPointInsertion) {
+TEST_F(LRUCacheTest, EntriesWithPriority) {
   // Allocate 2 cache entries to high-pri pool.
   NewCache(5, 0.45);