Webcron: Difference between revisions

Revision as of 09:46, 13 August 2015

Revision as of 01:23, 24 September 2015

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Users who set up premium accounts on third-party webcron scheduling providers typically{{really?|date=December 2010}} gain additional benefits such as [[SMS]] and [[email]] notifications, uptime reports and logging, increased timeout limits, schedules won't expire, being able to use [[HTTP POST]] method, [[HTTP cookie]] support, or fewer restrictions on scheduling frequency.<ref>[http://www.setcronjob.com/html/prices SetCronJob premium pricing page], retrieved October 14, 2010</ref><!--- This is just an example I randomly chose. There are a good 30 or so third-party scheduling providers that offer different benefits with premium accounts. --><ref name="easycronPlans"/>{{psc|date=December 2010}}{{or?|date=December 2010}}

Some webcron service providers accept [[Cron#CRON expression|CRON expression]] in web interface to schedule the job executing time.<ref name=webcronCronExp>[https://www.easycron.com/faq/What-cron-expression-does-easycron-support EasyCron accepts cron expression]</ref><ref name=setcron2>[https://www.setcron.com/help#crontab-features What are the crontab features of SetCron?]</ref>

=== Visitor Based ===

A webcron solution can be contained entirely on a web host by letting visitors trigger a webcron scheduler script on the server. For instance, this can be accomplished by using an [[img (HTML element)|'img' HTML element]] in the header or footer of the website, an [[ajax (programming)|Ajax]] call in a script or an [[HTML element#Frames|iFrame]]. When a visitor views the website, the image loads, which triggers the webcron scheduler. The webcron scheduler runs any tasks that need to run and then outputs an image so the visitor's web browser does not display a broken image on the page.<ref name="phpJobSched" /> It may alternatively start the task [[Non-blocking algorithm|asynchronously]] such that the [[HTTP]] response is not delayed.

If there are insufficient visitors to a website using visitor based webcron scheduling, then scheduled tasks will not run on time.