Sergey Zhuk has a new post to his site continuing on from a previous article about promises in ReactPHP. In this latest post he shows how you can use timers to cancel the execution of promises if their execution time grows too large.

At first, let’s refresh in memory what is Promise. A promise represents a result of an asynchronous operation. You can add fulfillment and error handlers to a promise object and they will be invoked once this operation has completed or failed. Check this article to learn more about promises.

Promise is a very powerful tool which allows us to pass around the code the eventual results of some deferred operation. But there is one problem with promises: they don’t give us much control.

He then shares the code required to make a simple "Hello world" promise and a handler for when it's cancelled. He then shows how to use the PromiseTimer functionality in ReactPHP to set a timeout on the promise instance and automatically call the cancellation event when it reaches that limit. He also includes a reminder that, in the cancellation handling of the promise it's a good idea to close out and cancel any other resources that may have been in use. The post ends with an example of how you can stack other functionality on the timeout using methods like "then" and "otherwise".