delayCacheWorkersStart option

Summary: Mirrors a similar option in CacheAllocatorConfig

Reviewed By: therealgymmy

Differential Revision: D47741160

fbshipit-source-id: 21cb9cb1436c28cd65b67af30eecd739da75f40f

Author: Anton Likhtarov

cachelib/experimental/objcache2/ObjectCache-inl.h

@@ -67,6 +67,9 @@ void ObjectCache<AllocatorT>::init() {
               item.getCreationTime(), item.getLastAccessTime()));
         };
       });
+  if (config_.delayCacheWorkersStart) {
+    l1Config.setDelayCacheWorkersStart();
+  }
 
   this->l1Cache_ = std::make_unique<AllocatorT>(l1Config);
   // add a pool per shard
@@ -103,7 +106,17 @@ void ObjectCache<AllocatorT>::init() {
     }
   }
 
-  initWorkers();
+  if (!config_.delayCacheWorkersStart) {
+    initWorkers();
+  }
+}
+
+template <typename AllocatorT>
+void ObjectCache<AllocatorT>::startCacheWorkers() {
+  if (config_.delayCacheWorkersStart) {
+    this->l1Cache_->startCacheWorkers();
+    initWorkers();
+  }
 }
 
 template <typename AllocatorT>

cachelib/experimental/objcache2/ObjectCache.h

@@ -411,6 +411,11 @@ class ObjectCache : public ObjectCacheBase<AllocatorT> {
     return success;
   }
 
+  // No-op for workers that are already running. Typically user uses this in
+  // conjunction with `config.setDelayCacheWorkersStart()` to avoid
+  // initialization ordering issues with user callback for cachelib's workers.
+  void startCacheWorkers();
+
  protected:
   // Serialize cache allocator config for exporting to Scuba
   std::map<std::string, std::string> serializeConfigParams() const override;

cachelib/experimental/objcache2/ObjectCacheConfig.h

@@ -140,6 +140,10 @@ struct ObjectCacheConfig {
 
   ObjectCacheConfig& setEvictionSearchLimit(uint32_t _evictionSearchLimit);
 
+  // We will delay worker start until user explicitly calls
+  // ObjectCache::startCacheWorkers()
+  ObjectCacheConfig& setDelayCacheWorkersStart();
+
   // With size controller disabled, above this many entries, L1 will start
   // evicting.
   // With size controller enabled, this is only a hint used for initialization.
@@ -224,6 +228,10 @@ struct ObjectCacheConfig {
   // 0 means it's infinite
   uint32_t evictionSearchLimit{50};
 
+  // If true, we will delay worker start until user explicitly calls
+  // ObjectCache::startCacheWorkers()
+  bool delayCacheWorkersStart{false};
+
   const ObjectCacheConfig& validate() const;
 };
 
@@ -388,6 +396,12 @@ ObjectCacheConfig<T>& ObjectCacheConfig<T>::setEvictionSearchLimit(
   return *this;
 }
 
+template <typename T>
+ObjectCacheConfig<T>& ObjectCacheConfig<T>::setDelayCacheWorkersStart() {
+  delayCacheWorkersStart = true;
+  return *this;
+}
+
 template <typename T>
 const ObjectCacheConfig<T>& ObjectCacheConfig<T>::validate() const {
   // checking missing params