chore: import upstream snapshot with attribution

python/ray/experimental/channel/cached_channel.py

@@ -0,0 +1,111 @@
+import uuid
+from typing import Any, Optional
+
+from ray.experimental.channel.common import ChannelInterface
+
+
+class CachedChannel(ChannelInterface):
+    """
+    CachedChannel wraps an inner channel and caches the data read from it until
+    `num_reads` reads have completed. If inner channel is None, the data
+    is written to serialization context and retrieved from there. This is useful
+    when passing data within the same actor and a shared memory channel can be
+    avoided.
+
+    Args:
+        num_reads: The number of reads from this channel that must happen before
+            writing again. Readers must be methods of the same actor.
+        inner_channel: The inner channel to cache data from. If None, the data is
+            read from the serialization context.
+        _channel_id: The unique ID for the channel. If None, a new ID is generated.
+    """
+
+    def __init__(
+        self,
+        num_reads: int,
+        inner_channel: Optional[ChannelInterface] = None,
+        _channel_id: Optional[str] = None,
+    ):
+        assert num_reads > 0, "num_reads must be greater than 0."
+        self._num_reads = num_reads
+        self._inner_channel = inner_channel
+        # Generate a unique ID for the channel. The writer and reader will use
+        # this ID to store and retrieve data from the _SerializationContext.
+        self._channel_id = _channel_id
+        if self._channel_id is None:
+            self._channel_id = str(uuid.uuid4())
+
+    def ensure_registered_as_writer(self) -> None:
+        if self._inner_channel is not None:
+            self._inner_channel.ensure_registered_as_writer()
+
+    def ensure_registered_as_reader(self) -> None:
+        if self._inner_channel is not None:
+            self._inner_channel.ensure_registered_as_reader()
+
+    def __reduce__(self):
+        return CachedChannel, (
+            self._num_reads,
+            self._inner_channel,
+            self._channel_id,
+        )
+
+    def __str__(self) -> str:
+        return (
+            f"CachedChannel(channel_id={self._channel_id}, "
+            f"num_reads={self._num_reads}), "
+            f"inner_channel={self._inner_channel})"
+        )
+
+    def write(self, value: Any, timeout: Optional[float] = None):
+        self.ensure_registered_as_writer()
+        # TODO: better organize the imports
+        from ray.experimental.channel import ChannelContext
+
+        if self._inner_channel is not None:
+            self._inner_channel.write(value, timeout)
+            return
+
+        # Otherwise no need to check timeout as the operation is non-blocking.
+
+        # Because both the reader and writer are in the same worker process,
+        # we can directly store the data in the context instead of storing
+        # it in the channel object. This removes the serialization overhead of `value`.
+        ctx = ChannelContext.get_current().serialization_context
+        ctx.set_data(self._channel_id, value, self._num_reads)
+
+    def read(self, timeout: Optional[float] = None) -> Any:
+        self.ensure_registered_as_reader()
+        # TODO: better organize the imports
+        from ray.experimental.channel import ChannelContext
+
+        ctx = ChannelContext.get_current().serialization_context
+        if ctx.has_data(self._channel_id):
+            # No need to check timeout as the operation is non-blocking.
+            return ctx.get_data(self._channel_id)
+
+        assert (
+            self._inner_channel is not None
+        ), "Cannot read from the serialization context while inner channel is None."
+        value = self._inner_channel.read(timeout)
+        ctx.set_data(self._channel_id, value, self._num_reads)
+        # NOTE: Currently we make a contract with Compiled Graph users that the
+        # channel results should not be mutated by the actor methods.
+        # When the user needs to modify the channel results, they should
+        # make a copy of the channel results and modify the copy.
+        # This is the same contract as used in IntraProcessChannel.
+        # This contract is NOT enforced right now in either case.
+        # TODO(rui): introduce a flag to control the behavior:
+        # for example, by default we make a deep copy of the channel
+        # result, but the user can turn off the deep copy for performance
+        # improvements.
+        # https://github.com/ray-project/ray/issues/47409
+        return ctx.get_data(self._channel_id)
+
+    def close(self) -> None:
+        from ray.experimental.channel import ChannelContext
+
+        if self._inner_channel is not None:
+            self._inner_channel.close()
+        ctx = ChannelContext.get_current().serialization_context
+        ctx.reset_data(self._channel_id)