Re
Do it again, if it doesn't work the first time. Supports various configurable
retry strategies, including: constant, exponential backoff and linear backoff.
Functions are styled after the async
library.
Install
npm install re
Usage
If you like the defaults, call it like this:
var retry = require('re'),
re = retry.Re();
re.try(function(retryCount, fail, callback){
if(retryCount < 2) fail(new Error("Not there yet!"));
else callback(retryCount);
},
function(retryCount){
console.log("It took this many tries: " + retryCount);
});
The re.try
function takes two arguments, a function to call until it works
(or we run out of retries) and a function to call when it finally succeeds (or
we fail too many times).
As the name suggests we automatically wrap your function in a standard try
block and, if an exception occurs, call it again according to the retry schedule.
This first function passed to re.try
should take 3 arguments like this:
function operation(retryCount, fail, callback)
The retryCount
argument is the number if the current retry. It'll be zero the first time
and get bigger every time.
The fail
argument is a function to call if you
encounter a fail condition in your operation. This let's us know we need to try again.
You can pass an err
argument to the fail
function.
The callback
argument is the callback function you passed into re.try
. It should be
a function that takes an err
parameter as it's first argument. The rest of the arguments
are up to you. Call this when you succeed. We'll call it with the last exception or whatever
you passed to the last fail
, when too many failures happen.
The re.do
function is like re.try
expect it doesn't wrap your operation in
a try...catch
.
Options
The default options look like this:
var options = {
retries : 10,
retryStrategy : {"type": retry.RETRY_STRATEGY.EXPONENTIAL, "initial":100, "base":2},
}
You pass this into the Re
constructor.
var re = retry.Re(options);
This gives you 10 retries and an exponential backoff strategy with the following progression (in milliseconds): 100, 200,
400, 800, 1600, 3200, 6400, 12800, 25600, 51200
Retry Strategy Examples
The following will retry every 400 milliseconds:
{"type": retry.RETRY_STRATEGY.CONSTANT, "initial": 400}
The following will give a linear backoff strategy that has the following progression (when paired with retries: 10
) : 200, 400, 600, 800, 1000, 1200, 1400, 1600, 1800, 1800
{"type": retry.RETRY_STRATEGY.LINEAR, "initial": 200, "max":1800}
Both progressive strategies take the max
option. All strategies also take a rand
option. This is a Boolean
that adds a random multiplier between 1 and 2. This makes them act like the tradition backoff function described here:
Exponential Backoff in Distributed Systems.
This parameter is set to false
by default.