So I needed an exponential backoff delay for reconnecting to our Websocket Server when our servers go down. I decided to implement it using a simple coroutine and the "redelay" command (reconnect delay). Exponential Backoff is used to schedule reconnects to a server so that when your server connection is re-established every instance of your scripts won't reconnect at the same exact time. If you want to learn more I found How to Reconnect Web Sockets in a Realtime Web App without Flooding the Server to be very helpful.
Basically it will generate a delay in ms for which is a random number between 1 second and the maximum delay. Each time you call the coroutine it will increase the maximum and return a new delay to use. You can set a name for the redelay or call it normally. You can also set the maximum seconds (default is 30) by using the second argument.
namespace eval redelay { variable count 0 } proc redelay { {name {}} {max 30} } { if {$name eq {}} { append name ::redelay::task [incr ::redelay::count] } return [coroutine $name ::redelay::delay $max] } proc ::redelay::delay { max } { yield [info coroutine] set attempts 1 while 1 { set interval [expr { min($max, (pow(2, $attempts) - 1)) * 1000 }] set delay [expr { int(rand()*($interval-1+1)+1) }] incr attempts if {[yield $delay] ne {}} { return } } }
Here is an example of it being used:
set d [redelay] set delay [$d] puts $delay set delay [$d] puts $delay set delay [$d] puts $delay $d break