{"id":37586,"date":"2022-11-08T17:01:41","date_gmt":"2022-11-08T22:01:41","guid":{"rendered":"https:\/\/mjtsai.com\/blog\/?p=37586"},"modified":"2022-11-09T13:09:04","modified_gmt":"2022-11-09T18:09:04","slug":"swift-concurrency-tips","status":"publish","type":"post","link":"https:\/\/mjtsai.com\/blog\/2022\/11\/08\/swift-concurrency-tips\/","title":{"rendered":"Swift Concurrency Tips"},"content":{"rendered":"

Wojciech Kulik<\/a> (Hacker News<\/a>):<\/p>\n

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If you add @MainActor<\/code> attribute to a function, it is not the same as wrapping the whole method in DispatchQueue.main.async<\/code>. If your method contains await<\/code> keyword, the code will be split into two pieces – one before await<\/code> and one after await<\/code>, and as mentioned before, once the method hits await<\/code> another pending call can start running even before the first one is finished.<\/p>\n

[…]<\/p>\n

You should remember to always mark a code with @MainActor<\/code> if you require the Main Thread. You shouldn’t make implicit assumptions. The problem is when you suddenly start adding async-await<\/code> to an existing project that was implemented without using Swift Concurrency. You can easily get into trouble if you don’t pay enough attention when mixing old code with async-await<\/code>.<\/p>\n

[…]<\/p>\n

First of all, you should avoid long-running synchronous work in Task<\/code>. For that, you should use GCD and custom queues. This way you will prevent blocking unintentionally some TaskPriority<\/code>. However, you should be also aware that having too many custom queues is not recommended because of possible Thread Explosion<\/a>. Therefore, you may try using OperationQueue<\/code> to limit concurrency.<\/p>\n

[…]<\/p>\n

[If] you test your code on a simulator each TaskPriority<\/code> will be limited to only 1 task running at the same time.<\/p>\n<\/blockquote>\n\n

Previously:<\/p>\n