Revert "Revert "feat: Add CacheProvider API for external distributed caching"" (Comfy-Org#12915)

* Revert "Revert "feat: Add CacheProvider API for external distributed caching …"

This reverts commit d1d53c1.

* fix: gate provider lookups to outputs cache and fix UI coercion

- Add `enable_providers` flag to BasicCache so only the outputs cache
  triggers external provider lookups/stores. The objects cache stores
  node class instances, not CacheEntry values, so provider calls were
  wasted round-trips that always missed.
- Remove `or {}` coercion on `result.ui` — an empty dict passes the
  `is not None` gate in execution.py and causes KeyError when the
  history builder indexes `["output"]` and `["meta"]`. Preserving
  `None` correctly skips the ui_node_outputs addition.

Author: deepme987

comfy_api/latest/__init__.py

@@ -25,6 +25,7 @@ def __init__(self):
         super().__init__()
         self.node_replacement = self.NodeReplacement()
         self.execution = self.Execution()
+        self.caching = self.Caching()
 
     class NodeReplacement(ProxiedSingleton):
         async def register(self, node_replace: io.NodeReplace) -> None:
@@ -84,6 +85,36 @@ async def set_progress(
                 image=to_display,
             )
 
+    class Caching(ProxiedSingleton):
+        """
+        External cache provider API for sharing cached node outputs
+        across ComfyUI instances.
+
+        Example::
+
+            from comfy_api.latest import Caching
+
+            class MyCacheProvider(Caching.CacheProvider):
+                async def on_lookup(self, context):
+                    ...  # check external storage
+
+                async def on_store(self, context, value):
+                    ...  # store to external storage
+
+            Caching.register_provider(MyCacheProvider())
+        """
+        from ._caching import CacheProvider, CacheContext, CacheValue
+
+        async def register_provider(self, provider: "ComfyAPI_latest.Caching.CacheProvider") -> None:
+            """Register an external cache provider. Providers are called in registration order."""
+            from comfy_execution.cache_provider import register_cache_provider
+            register_cache_provider(provider)
+
+        async def unregister_provider(self, provider: "ComfyAPI_latest.Caching.CacheProvider") -> None:
+            """Unregister a previously registered cache provider."""
+            from comfy_execution.cache_provider import unregister_cache_provider
+            unregister_cache_provider(provider)
+
 class ComfyExtension(ABC):
     async def on_load(self) -> None:
         """
@@ -116,6 +147,9 @@ class Types:
     VOXEL = VOXEL
     File3D = File3D
 
+
+Caching = ComfyAPI_latest.Caching
+
 ComfyAPI = ComfyAPI_latest
 
 # Create a synchronous version of the API
@@ -135,6 +169,7 @@ class Types:
     "Input",
     "InputImpl",
     "Types",
+    "Caching",
     "ComfyExtension",
     "io",
     "IO",

comfy_api/latest/_caching.py

@@ -0,0 +1,42 @@
+from abc import ABC, abstractmethod
+from typing import Optional
+from dataclasses import dataclass
+
+
+@dataclass
+class CacheContext:
+    node_id: str
+    class_type: str
+    cache_key_hash: str  # SHA256 hex digest
+
+
+@dataclass
+class CacheValue:
+    outputs: list
+    ui: dict = None
+
+
+class CacheProvider(ABC):
+    """Abstract base class for external cache providers.
+    Exceptions from provider methods are caught by the caller and never break execution.
+    """
+
+    @abstractmethod
+    async def on_lookup(self, context: CacheContext) -> Optional[CacheValue]:
+        """Called on local cache miss. Return CacheValue if found, None otherwise."""
+        pass
+
+    @abstractmethod
+    async def on_store(self, context: CacheContext, value: CacheValue) -> None:
+        """Called after local store. Dispatched via asyncio.create_task."""
+        pass
+
+    def should_cache(self, context: CacheContext, value: Optional[CacheValue] = None) -> bool:
+        """Return False to skip external caching for this node. Default: True."""
+        return True
+
+    def on_prompt_start(self, prompt_id: str) -> None:
+        pass
+
+    def on_prompt_end(self, prompt_id: str) -> None:
+        pass

comfy_execution/cache_provider.py

@@ -0,0 +1,138 @@
+from typing import Any, Optional, Tuple, List
+import hashlib
+import json
+import logging
+import threading
+
+# Public types — source of truth is comfy_api.latest._caching
+from comfy_api.latest._caching import CacheProvider, CacheContext, CacheValue  # noqa: F401 (re-exported)
+
+_logger = logging.getLogger(__name__)
+
+
+_providers: List[CacheProvider] = []
+_providers_lock = threading.Lock()
+_providers_snapshot: Tuple[CacheProvider, ...] = ()
+
+
+def register_cache_provider(provider: CacheProvider) -> None:
+    """Register an external cache provider. Providers are called in registration order."""
+    global _providers_snapshot
+    with _providers_lock:
+        if provider in _providers:
+            _logger.warning(f"Provider {provider.__class__.__name__} already registered")
+            return
+        _providers.append(provider)
+        _providers_snapshot = tuple(_providers)
+        _logger.debug(f"Registered cache provider: {provider.__class__.__name__}")
+
+
+def unregister_cache_provider(provider: CacheProvider) -> None:
+    global _providers_snapshot
+    with _providers_lock:
+        try:
+            _providers.remove(provider)
+            _providers_snapshot = tuple(_providers)
+            _logger.debug(f"Unregistered cache provider: {provider.__class__.__name__}")
+        except ValueError:
+            _logger.warning(f"Provider {provider.__class__.__name__} was not registered")
+
+
+def _get_cache_providers() -> Tuple[CacheProvider, ...]:
+    return _providers_snapshot
+
+
+def _has_cache_providers() -> bool:
+    return bool(_providers_snapshot)
+
+
+def _clear_cache_providers() -> None:
+    global _providers_snapshot
+    with _providers_lock:
+        _providers.clear()
+        _providers_snapshot = ()
+
+
+def _canonicalize(obj: Any) -> Any:
+    # Convert to canonical JSON-serializable form with deterministic ordering.
+    # Frozensets have non-deterministic iteration order between Python sessions.
+    # Raises ValueError for non-cacheable types (Unhashable, unknown) so that
+    # _serialize_cache_key returns None and external caching is skipped.
+    if isinstance(obj, frozenset):
+        return ("__frozenset__", sorted(
+            [_canonicalize(item) for item in obj],
+            key=lambda x: json.dumps(x, sort_keys=True)
+        ))
+    elif isinstance(obj, set):
+        return ("__set__", sorted(
+            [_canonicalize(item) for item in obj],
+            key=lambda x: json.dumps(x, sort_keys=True)
+        ))
+    elif isinstance(obj, tuple):
+        return ("__tuple__", [_canonicalize(item) for item in obj])
+    elif isinstance(obj, list):
+        return [_canonicalize(item) for item in obj]
+    elif isinstance(obj, dict):
+        return {"__dict__": sorted(
+            [[_canonicalize(k), _canonicalize(v)] for k, v in obj.items()],
+            key=lambda x: json.dumps(x, sort_keys=True)
+        )}
+    elif isinstance(obj, (int, float, str, bool, type(None))):
+        return (type(obj).__name__, obj)
+    elif isinstance(obj, bytes):
+        return ("__bytes__", obj.hex())
+    else:
+        raise ValueError(f"Cannot canonicalize type: {type(obj).__name__}")
+
+
+def _serialize_cache_key(cache_key: Any) -> Optional[str]:
+    # Returns deterministic SHA256 hex digest, or None on failure.
+    # Uses JSON (not pickle) because pickle is non-deterministic across sessions.
+    try:
+        canonical = _canonicalize(cache_key)
+        json_str = json.dumps(canonical, sort_keys=True, separators=(',', ':'))
+        return hashlib.sha256(json_str.encode('utf-8')).hexdigest()
+    except Exception as e:
+        _logger.warning(f"Failed to serialize cache key: {e}")
+        return None
+
+
+def _contains_self_unequal(obj: Any) -> bool:
+    # Local cache matches by ==. Values where not (x == x) (NaN, etc.) will
+    # never hit locally, but serialized form would match externally. Skip these.
+    try:
+        if not (obj == obj):
+            return True
+    except Exception:
+        return True
+    if isinstance(obj, (frozenset, tuple, list, set)):
+        return any(_contains_self_unequal(item) for item in obj)
+    if isinstance(obj, dict):
+        return any(_contains_self_unequal(k) or _contains_self_unequal(v) for k, v in obj.items())
+    if hasattr(obj, 'value'):
+        return _contains_self_unequal(obj.value)
+    return False
+
+
+def _estimate_value_size(value: CacheValue) -> int:
+    try:
+        import torch
+    except ImportError:
+        return 0
+
+    total = 0
+
+    def estimate(obj):
+        nonlocal total
+        if isinstance(obj, torch.Tensor):
+            total += obj.numel() * obj.element_size()
+        elif isinstance(obj, dict):
+            for v in obj.values():
+                estimate(v)
+        elif isinstance(obj, (list, tuple)):
+            for item in obj:
+                estimate(item)
+
+    for output in value.outputs:
+        estimate(output)
+    return total