Communicate with wireless devices. Configure devices. Interact with peripherals. Build user-space drivers. Manage devices. Create a build. Push an update. Chrome OS devices. App architecture. Architecture Components. UI layer libraries. View binding. Data binding library. Lifecycle-aware components. Paging Library. Paging 2. Data layer libraries. How-To Guides. Advanced Concepts.
Threading in WorkManager. App entry points. App shortcuts. App navigation. Navigation component. App links. Dependency injection. Core topics. App compatibility.
Interact with other apps. Package visibility. Intents and intent filters. User interface. Add motion to your layout with MotionLayout.
MotionLayout XML reference. Improving layout performance. Custom view components. Look and feel. Splash screens. Add the app bar. Control the system UI visibility. Supporting swipe-to-refresh. Pop-up messages overview. Adding search functionality. Creating backward-compatible UIs. Home channels for mobile apps. App widgets.
Media app architecture. Building an audio app. First of all, make sure you quit the app using the Stop button from Xcode. If you force-quit the app by swiping up from the app switcher the system cancels all background tasks:.
If the app is suspended the app process is terminated while a download is still in progress and then started again, if the download is still active, you can access the URLSession with the same identifier and it will resume notifications about the progress of the download.
For Android, you can set the minimumInterval option of your task to a small number and background your application like so:. See background tasks configuration guide for more details.
On Android, this module might listen when the device is starting up. It's necessary to continue working on tasks started with startOnBoot.
It also keeps devices "awake" that are going idle and asleep fast, to improve reliability of the tasks. This method doesn't take any effect on Android.
It is a global value which means that it can. Inexact interval in seconds between subsequent repeats of the background fetch alarm. The final interval may differ from the specified one to minimize wakeups and battery usage. Annie Kiley. Eli Fatsi. Noah Over. Contact Us. Explorations Code at Viget.
Newsletter Apples and Oranges. Article Dev Book Club. A Brief History In the olden days, the maximum amount of work per CPU cycle that a computer could perform was determined by the clock speed. How can we take advantage of these extra cores?
The Burden of Threads A modern multitasking operating system like iOS has hundreds of programs or processes running at any given moment. In addition to building an app, the developer has to: Responsibly create new threads, adjusting that number dynamically as system conditions change Manage them carefully, deallocating them from memory once they have finished executing Leverage synchronization mechanisms like mutexes, locks, and semaphores to orchestrate resource access between threads, adding even more overhead to application code Mitigate risks associated with coding an application that assumes most of the costs associated with creating and maintaining any threads it uses, and not the host OS This is unfortunate, as it adds enormous levels of complexity and risk without any guarantees of improved performance.
Grand Central Dispatch iOS takes an asynchronous approach to solving the concurrency problem of managing threads. Let's take a look at the main components of GCD:. What've we got here? Let's start from the left: DispatchQueue. All tasks are executed in succession, so it is guaranteed that the order of execution is preserved. It is crucial that you ensure all UI updates are designated to this queue, and that you never run any blocking tasks on it.
We want to ensure that the app's run loop called CFRunLoop is never blocked in order to maintain the highest framerate. Subsequently, the main queue has the highest priority, and any tasks pushed onto this queue will get executed immediately. Depending on the priority of your task, you can specify which specific queue to execute your task on, although you should resort to using default most of the time.
Because tasks on these queues are executed concurrently, it doesn't guarantee preservation of the order in which tasks were queued. Serial Queues: The Main Thread As an exercise, let's look at a snippet of code below, which gets fired when the user presses a button in the app. Background Threads How can we make this better? A Note on Main Thread vs.
Concurrent Queues So far, our tasks have been executed exclusively in a serial manner. Parallelization of N Tasks So far, we've looked at pushing computationally expensive task s onto background threads without clogging up the UI thread. Finer Control with OperationQueue GCD is great when you want to dispatch one-off tasks or closures into a queue in a 'set-it-and-forget-it' fashion, and it provides a very lightweight way of doing so.
Let's look at some of the benefits of using these abstractions and what they offer in comparison to the lower-level GCI API: You may want to create dependencies between tasks , and while you could do this via GCD, you're better off defining them concretely as Operation objects, or units of work, and pushing them onto your own queue.
This would allow for maximum reusability since you may use the same pattern elsewhere in an application. This is another important benefit if you want to monitor the state of an operation or operation queue.
Operations can be paused, resumed, and cancelled. Once you dispatch a task using Grand Central Dispatch, you no longer have control or insight into the execution of that task. The Operation API is more flexible in that respect, giving the developer control over the operation's life cycle.
OperationQueue allows you to specify the maximum number of queued operations that can run simultaneously, giving you a finer degree of control over the concurrency aspects. In the simplest form it might look like this:. A high-level diagram shows all major system components and their interactions without implementation details. You can learn more about high-level diagrams here. After a high-level discussion, your interviewer might want to discuss some specific components of the system.
You can learn more about deep-dive discussions here. The active jobs are dispatched by download workers. A Download Worker is responsible for actual data transmission from the network.
For example, the same video file can be included in multiple playlists. The user can download these playlists in parallel — as a result, there might be different jobs for the same worker. Some interviewers might ask follow-up questions that might change the original design and introduce new requirements.
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