Performance

osra’s overhead is small and predictable: one platform channel per connection, O(1) dispatch per message, and a boxing walk per payload. This page covers where the costs are and how to avoid the avoidable ones.

One connection, one channel

One connection = one platform channel. Every live value — functions, promises, streams, ports — multiplexes over it as message envelopes, with O(1) per-portId dispatch on each side. Adding more live values doesn’t add channels; it adds routing entries in a map. See Architecture for how portId routing works.

Per-call cost

Each remote function call allocates:

• a synthetic return channel,
• one routing entry on each side,
• one boxing walk of the arguments.

Entries are dropped when the result settles. Chatty fine-grained calls are fine; batching is still cheaper.

Large binary data

On structured-clone transports, wrap buffers in transfer() to move instead of copy — a 16 MB ArrayBuffer transfers without a byte copied (see identity() and transfer()).

Real MessagePorts are must-transfer and always moved. Streams are not: the stream modules claim them first and replace them with a port channel, so chunks are proxied message-by-message with per-chunk boxing/copying — even under transfer(). For bulk binary data, prefer transferring buffers over streaming them when you can.

On JSON transports, ArrayBuffer and TypedArrays serialize to base64, which costs both size and CPU; transfer() degrades to a copy there. See JSON vs clone transports.

Repeat sends: identity() dedupes

identity(obj) dedupes repeat sends: the first send ships the payload plus an id, later sends of the same reference ship only the id, and the peer reuses its cached revived value. A round-trip resolves back to your original object. If you pass the same large object to the peer repeatedly, wrap it once in identity() and pay the serialization cost once.

Keep envelopes lean

Boxing walks plain objects and arrays recursively, so payload shape is a direct cost. Keep envelopes lean: send what the call needs rather than dragging large ambient structures through every payload.