feat: Batching

ios/MmkvHostObject.mm

@@ -295,6 +295,38 @@
       return jsi::Value::undefined();
     });
   }
+
+  if (propName == "applyBatchedWrites") {
+    // MMKV.applyBatchedWrites(Map<K, V>, DELETE_SYMBOL)
+    return jsi::Function::createFromHostFunction(runtime,
+                                                 jsi::PropNameID::forAscii(runtime, funcName),
+                                                 1, // encryptionKey
+                                                 [this](jsi::Runtime& runtime,
+                                                        const jsi::Value& thisValue,
+                                                        const jsi::Value* arguments,
+                                                        size_t count) -> jsi::Value {
+      auto run = [this](jsi::Runtime& runtime,
+                        const jsi::Value& thisValue,
+                        const jsi::Value* arguments,
+                        size_t count) -> jsi::Value {
+        auto resolve = arguments[0].asObject(runtime).asFunction(runtime);
+
+        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+          // TODO: Read from Map and apply everything here?
+
+          // TODO: Resolve on CallInvoker
+        });
+
+        return jsi::Value::undefined();
+      };
+
+      auto newPromise = runtime.global().getPropertyAsFunction(runtime, "Promise");
+      auto runFunction = jsi::Function::createFromHostFunction(runtime, jsi::PropNameID::forAscii(runtime, "Promise::run"), 1, std::move(run));
+
+      return newPromise.callAsConstructor(runtime, runFunction, 1);
+    });
+
+  }
 
   return jsi::Value::undefined();
 }

src/MMKV.ts

@@ -1,5 +1,6 @@
 import { createMMKV } from './createMMKV';
 import { createMockMMKV } from './createMMKV.mock';
+import { DELETE_SYMBOL, MemoryCache, MemoryCacheMap } from './MemoryCache';
 import { isJest } from './PlatformChecker';
 
 interface Listener {
@@ -125,7 +126,12 @@ export type NativeMMKV = Pick<
   | 'getBuffer'
   | 'set'
   | 'recrypt'
->;
+> & {
+  applyBatchedWrites: (
+    map: MemoryCacheMap,
+    deleteFlag: typeof DELETE_SYMBOL
+  ) => Promise<void>;
+};
 
 const onValueChangedListeners = new Map<string, ((key: string) => void)[]>();
 
@@ -233,6 +239,37 @@ export class MMKV implements MMKVInterface {
     };
   }
 
+  /**
+   * Creates a proxy of the MMKV instance that writes all new operations to an
+   * in-memory `Map<K, V>` instead of writing it to the  file.
+   * The Map can later be used to apply all writes in a single batch.
+   */
+  private createInMemoryCopy(memoryCache: MemoryCache): MMKVInterface {
+    return {
+      addOnValueChangedListener: this.addOnValueChangedListener,
+      clearAll: memoryCache.clear,
+      contains: memoryCache.has,
+      delete: memoryCache.delete,
+      getAllKeys: memoryCache.getAllKeys,
+      getBoolean: memoryCache.getBoolean,
+      getBuffer: memoryCache.getBuffer,
+      getNumber: memoryCache.getNumber,
+      getString: memoryCache.getString,
+      recrypt: this.recrypt,
+      set: memoryCache.set,
+    };
+  }
+
+  batch(callback: (storage: MMKVInterface) => void): Promise<void> {
+    const memoryCache = new MemoryCache(this);
+    const copy = this.createInMemoryCopy(memoryCache);
+    callback(copy);
+    return this.nativeInstance.applyBatchedWrites(
+      memoryCache.map,
+      DELETE_SYMBOL
+    );
+  }
+
   addOnValueChangedListener(onValueChanged: (key: string) => void): Listener {
     this.onValueChangedListeners.push(onValueChanged);
 

src/MemoryCache.ts

@@ -0,0 +1,103 @@
+import type { MMKV } from './MMKV';
+
+export const DELETE_SYMBOL = Symbol();
+export const NOT_YET_LOADED_SYMBOL = Symbol();
+
+type ValueType = string | boolean | number | Uint8Array;
+type NOT_YET_LOADED = typeof NOT_YET_LOADED_SYMBOL;
+type WILL_DELETE = typeof DELETE_SYMBOL;
+
+export type MemoryCacheMap = Map<
+  string,
+  ValueType | NOT_YET_LOADED | WILL_DELETE
+>;
+
+export class MemoryCache {
+  map: MemoryCacheMap;
+  private mmkv: MMKV;
+
+  constructor(mmkv: MMKV) {
+    this.map = new Map();
+    this.mmkv = mmkv;
+
+    // init all keys, values are not yet loaded though.
+    for (const key of mmkv.getAllKeys()) {
+      this.map.set(key, NOT_YET_LOADED_SYMBOL);
+    }
+  }
+
+  has(key: string): boolean {
+    const value = this.map.get(key);
+    if (value == null) return false;
+    if (value === DELETE_SYMBOL) return false;
+    return true;
+  }
+
+  getAllKeys(): string[] {
+    const keys: string[] = [];
+    this.map.forEach((value, key) => {
+      if (value !== DELETE_SYMBOL) keys.push(key);
+    });
+    return keys;
+  }
+
+  private get<T extends 'getBoolean' | 'getString' | 'getNumber' | 'getBuffer'>(
+    key: string,
+    method: T
+  ): ValueType | undefined {
+    const value = this.map.get(key);
+
+    if (value === NOT_YET_LOADED_SYMBOL) {
+      const nativeValue = this.mmkv[method](key);
+      if (nativeValue != null) {
+        this.map.set(key, nativeValue);
+        return nativeValue;
+      } else {
+        return undefined;
+      }
+    }
+    if (value === DELETE_SYMBOL) {
+      return undefined;
+    }
+
+    return value;
+  }
+
+  getBoolean(key: string): boolean | undefined {
+    const value = this.get(key, 'getBoolean');
+    if (typeof value === 'boolean') return value;
+    else return undefined;
+  }
+
+  getString(key: string): string | undefined {
+    const value = this.get(key, 'getString');
+    if (typeof value === 'string') return value;
+    else return undefined;
+  }
+
+  getNumber(key: string): number | undefined {
+    const value = this.get(key, 'getNumber');
+    if (typeof value === 'number') return value;
+    else return undefined;
+  }
+
+  getBuffer(key: string): Uint8Array | undefined {
+    const value = this.get(key, 'getBuffer');
+    if (value instanceof Uint8Array) return value;
+    else return undefined;
+  }
+
+  set(key: string, value: ValueType): void {
+    this.map.set(key, value);
+  }
+
+  delete(key: string): void {
+    this.map.set(key, DELETE_SYMBOL);
+  }
+
+  clear(): void {
+    for (const key of this.map.keys()) {
+      this.delete(key);
+    }
+  }
+}