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Async broadcast to websocket handles using internal function -25!
Hi,
I try to subscribe table in KDB server from a javascript client using websocket and receive message from KDB server. The websocket connection is good, and I can get the handle (assume the handle is 10). However, when I try to publish data to javascript client using -25!(enlist 10; msg), it throws an error: 10 is not an ipc handle. I have checked the connection is still alive, and I can publish data to client using neg[10] msg. So is there any constraints on async broadcast(-25!)? Can someone help me with this? Thanks a lot!
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2 Replies
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-25! is for use with IPC handles only. Not websocket handles.
The reason is for IPC handles there is a serialization step and here -25! is efficient in allowing this to only be run once for many handles.
For websocket handles data is sent directly without any serialization step, -25! would offer no benefit here.
- https://code.kx.com/q/basics/internal/#-25x-async-broadcast
- https://code.kx.com/q/basics/internal/#-38x-socket-table
q){([]h)!-38!h:.z.H}[] h | p f ---| --- 612| w t 580| q t q)-25!(enlist 612i;"test") '612 is not an ipc handle [0] -25!(enlist 612i;"test") ^ q)-25!(enlist 580i;"test")For websockets if there is a large operation like converting a table to JSON you can control this being done once and then sent to multiple websockets:
neg[webSockethandles]@:.j.j bigTable
Wrapping the same in a helper:
wsBroadcast:{[handles;data] neg[(),handles]@:data} wsBroadcast[myWebsocketHandles] .j.j bigTable
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Thanks a lot rocuinneagain! I assumed websocket handles were also IPC handles. -38! gives me the answer. Again very appreciate for your detailed reply
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