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Chris Tate
21b88b8d66
new MessageChannel() from node:worker_threads makes two entangled
MessagePorts. They share the handle model of parentPort: postMessage
with the existing message clone, 'message' and 'close' events,
on/once, start, close, ref, unref and hasRef. A port's 'close' reaches
the other port after its queued messages. receiveMessageOnPort(port)
answers the next queued message as { message }, or undefined.
A channel is a thread-neutral record (scr_mailbox.c): each end has its
queue and the inbox of the thread that owns its port. A port listed in a
transfer list, given as postMessage's array or { transfer }, or as the
Worker constructor's transferList, travels with the message, and the
decoding thread adopts it. The sending port becomes unusable. A port in a
message without that listing throws DataCloneError, and so does a port
listing itself.
Port events follow Node's loop phases. Each port's queued messages
arrive as one batch, ports in creation order, before setImmediate
callbacks, with nextTicks and microtasks after each message (a new loop
hook keeps the pass going until the batch is delivered). A port's own
'close' runs in the following close phase, the latest close() first. The
other port's 'close' arrives on a later poll, in the order the notices
were sent, and only while the loop keeps running.