Fabric: Introducing SimpleThreadSafeCache

Summary: SimpleThreadSafeCache is a simple thread-safe LRU cache; it's a generalized version of ParagraphMeasurementCache.

Reviewed By: mdvacca

Differential Revision: D14296516

fbshipit-source-id: 2b40ac1979ada12551848ece3642b2d99e369672

ReactCommon/utils/BUCK

@@ -26,6 +26,10 @@ rn_xplat_cxx_library(
         "PUBLIC",
     ],
     deps = [
+        "fbsource//xplat/folly:evicting_cache_map",
+        "fbsource//xplat/folly:headers_only",
+        "fbsource//xplat/folly:memory",
+        "fbsource//xplat/folly:molly",
         react_native_xplat_target("better:better"),
     ],
 )

ReactCommon/utils/SimpleThreadSafeCache.h

@@ -0,0 +1,74 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <functional>
+#include <memory>
+#include <mutex>
+
+#include <better/optional.h>
+#include <folly/container/EvictingCacheMap.h>
+
+namespace facebook {
+namespace react {
+
+/*
+ * Simple thread-safe LRU cache.
+ */
+template<typename KeyT, typename ValueT, int maxSize>
+class SimpleThreadSafeCache {
+public:
+  SimpleThreadSafeCache() : map_{maxSize} {}
+
+  /*
+   * Returns a value from the map with a given key.
+   * If the value wasn't found in the cache, constructs the value using given
+   * generator function, stores it inside a cache and returns it.
+   * Can be called from any thread.
+   */
+  ValueT get(const KeyT &key, std::function<ValueT(const KeyT &key)> generator) const {
+    std::lock_guard<std::mutex> lock(mutex_);
+    auto iterator = map_.find(key);
+    if (iterator == map_.end()) {
+      auto value = generator(key);
+      map_.set(key, value);
+      return value;
+    }
+
+    return iterator->second;
+  }
+
+  /*
+   * Returns a value from the map with a given key.
+   * If the value wasn't found in the cache, returns empty optional.
+   * Can be called from any thread.
+   */
+  better::optional<ValueT> get(const KeyT &key) const {
+    std::lock_guard<std::mutex> lock(mutex_);
+    auto iterator = map_.find(key);
+    if (iterator == map_.end()) {
+      return {};
+    }
+
+    return iterator->second;
+  }
+
+  /*
+   * Sets a key-value pair in the LRU cache.
+   * Can be called from any thread.
+   */
+  void set(const KeyT &key, const ValueT &value) const {
+    std::lock_guard<std::mutex> lock(mutex_);
+    map_.set(std::move(key), std::move(value));
+  }
+
+private:
+  mutable folly::EvictingCacheMap<KeyT, ValueT> map_;
+  mutable std::mutex mutex_;
+};
+
+} // namespace react
+} // namespace facebook