AsyncMachine Exception Example

node v8.17.0

version: master

This example presents a simple fault tolerance (retrying) using the Exception state. Scroll down to see the log output. https://github.com/TobiaszCudnik/asyncmachine

const { machine } = require('asyncmachine') const example = machine(['Stable', 'Broken']) .id('') .logLevel(2) // state negotiation example.Broken_enter = function() { let clock = this.clock('Exception') console.log(`Exception clock == ${clock}`) if (clock > 5) { console.log('Too many errors, quitting') return false } } // state set example.Broken_state = function() { throw Error('random exception') } // use the state negotiation for fault tolerance example.Exception_state = function( err, target_states, base_states, exception_src_handler, async_target_states ) { // try to rescue the Broken state if (target_states.includes('Broken')) { console.log('Retrying the Broken state') this.drop('Exception') this.add('Broken') } } example.add(['Stable', 'Broken']) example.is()

Log output (level 2): [add] Stable, Broken [transition] Broken_enter Exception clock == 0 [state] +Stable +Broken [transition] Broken_state [exception] from Broken, forced states to Stable [state:force] Stable [add] Exception [state] +Exception [transition] Exception_state Retrying the Broken state [queue:drop] Exception [queue:add] Broken [drop] Exception [state] -Exception [add] Broken [transition] Broken_enter Exception clock == 1 [state] +Broken [transition] Broken_state [exception] from Broken, forced states to Stable [state:force] Stable [add] Exception [state] +Exception [transition] Exception_state Retrying the Broken state [queue:drop] Exception [queue:add] Broken [drop] Exception [state] -Exception [add] Broken [transition] Broken_enter Exception clock == 2 [state] +Broken [transition] Broken_state [exception] from Broken, forced states to Stable [state:force] Stable [add] Exception [state] +Exception [transition] Exception_state Retrying the Broken state [queue:drop] Exception [queue:add] Broken [drop] Exception [state] -Exception [add] Broken [transition] Broken_enter Exception clock == 3 [state] +Broken [transition] Broken_state [exception] from Broken, forced states to Stable [state:force] Stable [add] Exception [state] +Exception [transition] Exception_state Retrying the Broken state [queue:drop] Exception [queue:add] Broken [drop] Exception [state] -Exception [add] Broken [transition] Broken_enter Exception clock == 4 [state] +Broken [transition] Broken_state [exception] from Broken, forced states to Stable [state:force] Stable [add] Exception [state] +Exception [transition] Exception_state Retrying the Broken state [queue:drop] Exception [queue:add] Broken [drop] Exception [state] -Exception [add] Broken [transition] Broken_enter Exception clock == 5 [state] +Broken [transition] Broken_state [exception] from Broken, forced states to Stable [state:force] Stable [add] Exception [state] +Exception [transition] Exception_state Retrying the Broken state [queue:drop] Exception [queue:add] Broken [drop] Exception [state] -Exception [add] Broken [transition] Broken_enter Exception clock == 6 Too many errors, quitting [cancelled] Broken, Stable by the method Broken_enter state [ 'Stable' ]

AsyncMachine Exception Example

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