Locking the command is basically a double run prevention.<\/p>\n
Assume that you have a hourly email command and you’re sending e-mails to users one by one. If the command doesn’t finish until next hour, you may send multiple e-mails to some users. Or your colleague can try to start same command after you run it.<\/p>\n
<?php\n\/\/ RUN A:\n$users = User::where('hourly_email_sent', false)->get();\n\/\/ On above query, 10.000 users have been found. \n\/\/ The command started and already processed 8.000 users in one hour. There are 2.000 users remaining.\n\/\/ If you start command again, you'll send 2 emails for remaining 2.000 users. Because a command is already running and you started another one.\n\n\/\/ RUN B:\n$users = User::where('hourly_email_sent', false)->get();\n\/\/ On above query 2000+ users have been found.\n\/\/ RUN A and RUN B can contain same users!<\/code><\/pre>\nI generally prefer to put a value to cache and check it before actually running the command. Here’s an example:<\/p>\n
<?php\n\n$cacheLockKey = 'command_name';\nif (Cache::has($cacheLockKey)) \n{\n $this->output->writeln('Another process is already running. Exiting...');\n\n return 1;\n}\n\nCache::put($cacheLockKey, date('Y-m-d H:i:s'));\n\n\/\/ do some logic\n\nCache::forget($cacheLockKey);\n\nreturn 0;<\/code><\/pre>\nThis simple control will prevent you to run a command twice with mistake. It’s easy, isn’t it?<\/p>\n
Downsides with putting lock into cache<\/h2>\n
You can use database or file storage too. I didn’t get trouble just because I’m using cache, but of course you can get problems somehow.<\/p>\n
If cache gets flushed for all values, your cache key will also be removed. You have to protect your lock until command is really finished.<\/p>\n
If you have multiple servers, you have to make sure all servers are using same cache storage.<\/p>\n
Failure Case<\/h2>\n
If the command fails for a reason, you have to be sure cache key was removed. Otherwise command won’t start again.<\/p>\n
You can handle this situation manually, but if you’re running command on cronjob, your next run may not be able to succeed.<\/p>\n
This failure case of course depends whatever you want from a job.<\/p>\n","protected":false},"excerpt":{"rendered":"
Locking the command is basically a double run prevention. Assume that you have a hourly email command and you’re sending e-mails to users one by one. If the command doesn’t finish until next hour, you may send multiple e-mails to some users. Or your colleague can try to start same command after you run it. […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[763],"tags":[767],"class_list":["post-2272","post","type-post","status-publish","format-standard","hentry","category-development-and-internet","tag-writing-command-line-applications-en"],"blocksy_meta":{"styles_descriptor":{"styles":{"desktop":"","tablet":"","mobile":""},"google_fonts":[],"version":6}},"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_likes_enabled":true,"jetpack-related-posts":[],"jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/guven.atbakan.com\/blog\/wp-json\/wp\/v2\/posts\/2272","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/guven.atbakan.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/guven.atbakan.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/guven.atbakan.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/guven.atbakan.com\/blog\/wp-json\/wp\/v2\/comments?post=2272"}],"version-history":[{"count":22,"href":"https:\/\/guven.atbakan.com\/blog\/wp-json\/wp\/v2\/posts\/2272\/revisions"}],"predecessor-version":[{"id":2392,"href":"https:\/\/guven.atbakan.com\/blog\/wp-json\/wp\/v2\/posts\/2272\/revisions\/2392"}],"wp:attachment":[{"href":"https:\/\/guven.atbakan.com\/blog\/wp-json\/wp\/v2\/media?parent=2272"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/guven.atbakan.com\/blog\/wp-json\/wp\/v2\/categories?post=2272"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/guven.atbakan.com\/blog\/wp-json\/wp\/v2\/tags?post=2272"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}