Broadcast an Async Message to Multiple Handles

Question

What is an asynchronous broadcast, and how does it differ from sending the same message to each handle individually?

Solution

handles:hopen each 8001 8002     / two processes listening on ports 8001 and 8002
msg:(`upd;`trade;([] sym:enlist`AAPL; price:enlist 185.2))
-25!(handles;msg)

Alternative Solution

neg[handles]@\:msg

Explanation

-25! queues the same async message for delivery on a list of handles at once. neg[handles]@\:msg does the same job with each-left, but serialises msg separately for every handle. -25! serialises it once and reuses that for every handle — much cheaper for fanning the same update out to many connections, like a tickerplant pushing ticks to all its subscribers.

Since one serialised form has to suit every recipient, -25! serialises to the lowest IPC capability among the target handles (relevant when the recipients run different kdb+ versions). If there is an error, no messages are sent, and -25! returns the handle that caused it.

Like any async send, the message is only queued, not necessarily flushed immediately. It can be flushed manually:

neg[handles]@\:(::)
/ or
-25!(handles;::)