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 $delay] ne {}} { return }
}
}
Here is an example of it being used (your delays will vary from the ones shown here since it is using random)
set d [redelay] ; # ::redelay::task1 puts [$d] ; # 566 puts [$d] ; # 2071 puts [$d] ; # 1303 puts [$d] ; # 5375 puts [$d] ; # 24724 puts [$d] ; # 9369 puts [$d] ; # 11873 puts [$d] ; # 4104 $d break