Async broadcast to websocket handles using internal function -25!

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1

https://learninghub.kx.com/forums/topic/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!

2

-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.

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

 

3

Thanks a lot rocuinneagain! I assumed websocket handles were also IPC handles. -38! gives me the answer. Again very appreciate for your detailed reply