✨ feat(flow.py): add InMemoryCache class to implement an in-memory cache with LRU eviction policy

This commit adds a new class InMemoryCache to implement an in-memory cache with a Least Recently Used (LRU) eviction policy. The cache supports setting a maximum size and expiration time for cached items. The cache is thread-safe using a threading Lock. The InMemoryCache class inherits from the BaseCache class and implements the get, set, get_or_set, delete, clear, __contains__, __getitem__, __setitem__, __delitem__, __len__, and __repr__ methods.

src/backend/langflow/cache/flow.py

@@ -0,0 +1,146 @@
+import threading
+import time
+from collections import OrderedDict
+
+from langflow.cache.base import BaseCache
+
+
+class InMemoryCache(BaseCache):
+    """
+    A simple in-memory cache using an OrderedDict.
+
+    This cache supports setting a maximum size and expiration time for cached items.
+    When the cache is full, it uses a Least Recently Used (LRU) eviction policy.
+    Thread-safe using a threading Lock.
+
+    Attributes:
+        max_size (int, optional): Maximum number of items to store in the cache.
+        expiration_time (int, optional): Time in seconds after which a cached item expires. Default is 1 hour.
+
+    Example:
+
+        cache = InMemoryCache(max_size=3, expiration_time=5)
+
+        # setting cache values
+        cache.set("a", 1)
+        cache.set("b", 2)
+        cache["c"] = 3
+
+        # getting cache values
+        a = cache.get("a")
+        b = cache["b"]
+    """
+
+    def __init__(self, max_size=None, expiration_time=60 * 60):
+        """
+        Initialize a new InMemoryCache instance.
+
+        Args:
+            max_size (int, optional): Maximum number of items to store in the cache.
+            expiration_time (int, optional): Time in seconds after which a cached item expires. Default is 1 hour.
+        """
+        self._cache = OrderedDict()
+        self._lock = threading.Lock()
+        self.max_size = max_size
+        self.expiration_time = expiration_time
+
+    def get(self, key):
+        """
+        Retrieve an item from the cache.
+
+        Args:
+            key: The key of the item to retrieve.
+
+        Returns:
+            The value associated with the key, or None if the key is not found or the item has expired.
+        """
+        with self._lock:
+            if key in self._cache:
+                item = self._cache.pop(key)
+                if (
+                    self.expiration_time is None
+                    or time.time() - item["time"] < self.expiration_time
+                ):
+                    # Move the key to the end to make it recently used
+                    self._cache[key] = item
+                    return item["value"]
+                else:
+                    self.delete(key)
+            return None
+
+    def set(self, key, value):
+        """
+        Add an item to the cache.
+
+        If the cache is full, the least recently used item is evicted.
+
+        Args:
+            key: The key of the item.
+            value: The value to cache.
+        """
+        with self._lock:
+            if key in self._cache:
+                # Remove existing key before re-inserting to update order
+                self.delete(key)
+            elif self.max_size and len(self._cache) >= self.max_size:
+                # Remove least recently used item
+                self._cache.popitem(last=False)
+            self._cache[key] = {"value": value, "time": time.time()}
+
+    def get_or_set(self, key, value):
+        """
+        Retrieve an item from the cache. If the item does not exist, set it with the provided value.
+
+        Args:
+            key: The key of the item.
+            value: The value to cache if the item doesn't exist.
+
+        Returns:
+            The cached value associated with the key.
+        """
+        with self._lock:
+            if key in self._cache:
+                return self.get(key)
+            self.set(key, value)
+            return value
+
+    def delete(self, key):
+        """
+        Remove an item from the cache.
+
+        Args:
+            key: The key of the item to remove.
+        """
+        # with self._lock:
+        self._cache.pop(key, None)
+
+    def clear(self):
+        """
+        Clear all items from the cache.
+        """
+        with self._lock:
+            self._cache.clear()
+
+    def __contains__(self, key):
+        """Check if the key is in the cache."""
+        return key in self._cache
+
+    def __getitem__(self, key):
+        """Retrieve an item from the cache using the square bracket notation."""
+        return self.get(key)
+
+    def __setitem__(self, key, value):
+        """Add an item to the cache using the square bracket notation."""
+        self.set(key, value)
+
+    def __delitem__(self, key):
+        """Remove an item from the cache using the square bracket notation."""
+        self.delete(key)
+
+    def __len__(self):
+        """Return the number of items in the cache."""
+        return len(self._cache)
+
+    def __repr__(self):
+        """Return a string representation of the InMemoryCache instance."""
+        return f"InMemoryCache(max_size={self.max_size}, expiration_time={self.expiration_time})"