HTML5 Multithreading
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Web workers allow long-running scripts to run in background threads separate from the main thread of a web page, in order to avoid making the page unresponsive. They enable running scripts across threads and processing large data sets concurrently. Web workers communicate with the main thread through messaging and have access to some but not all browser APIs. There are different types of web workers including dedicated, shared, and inline workers that have different scopes and capabilities.
HTML5 Multithreading
- 2. Agenda Single Threaded Model Unresponsive Script Multithreading Web Workers (Dedicated) Sub Web Workers Shared Web Workers
- 4. Single Threaded Model JavaScript in a browser executes on a Single Thread Asynchronous Events Timer Delay is Not Guaranteed!
- 5. Unresponsive Script Browser complains a long-running script and ask user if it should be stopped
- 6. Unresponsive Script Solutions setTimeout() Use 1ms timeout chunks cause task to complete slowly overall, but browser UI will remain responsive Web Workers Web workers provide background thread support in the browser
- 8. Web Workers Dedicated Web Workers Allow long-running script that are not interrupted by scripts that respond to clicks or other user interactions Allows long tasks to be executed without yielding to keep the page responsive Checking for Browser Support Compatibility Tables if (typeof(window.Worker) !== ‘undefined’) { // this browser supports web workers }
- 9. Workers Environment Accessible The this / self object (worker) The navigator object The read-only location object XMLHttpRequest setTimeout() / clearTimeout() setInterval() / clearInterval() The Application Cache Inaccessible Web Sockets Web Data Storage The DOM (thread-unsafe!) The window objects The document object The parent object Communicate with DOM by message passing
- 10. Communication with Workers Use postMessage() to send data to and from Web Workers for cross-pages (sub windows / internal frames) communication postMessage() can be used to send most JavaScript objects, but Not JavaScript Functions or Objects with Cyclic References, since JSON doesn't support these
- 11. Web Workers
- 12. Stop Workers Call worker.terminate() from the main page Call self.close() inside of the worker itself
- 13. Handling Errors e.message e.filename A human-readable error message The name of the script file in which the error occurred e.lineno The line number of the script file on which the error occurred
- 14. Sub Web Workers Workers have the ability to spawn sub workers, but… Sub-workers must be hosted within the same origin as the parent page The URIs for sub workers are resolved relative to the parent worker's location rather than that of the owning page
- 15. Sub Web Workers
- 16. Shared Web Workers Shared Web Worker can be shared across pages (popups / iframes) on the same origin Introduce the notion of ports that are used for postMessage() communication Be useful for data synchronization among multiple pages (or tabs) on the same origin or to share a long-lived resource (like a WebSocket) among several tabs
- 18. Inline Web Workers Inline Web Workers which are created in the same web page context or on the fly Page Inline Worker Reduce the number of requests that the page perform Create some functionality on the fly The worker's code is created inline inside the web page <script type="javascript/worker"> On The Fly Worker The worker’s code is provided by an external source as string
- 20. Loading External Scripts Workers have access to a importScripts API which lets them import scripts into their scope importScripts('script1.js'); importScripts('script2.js'); importScripts('script1.js', 'script2.js'); Scripts may be downloaded in any order, but will be executed in the order in which you pass the filenames
- 21. Use Cases Performing computations in the background Performing web I/O in the background Code syntax highlighting Real-time text formatting Spell / Grammar checker Pre-fetching and/or caching data Background I/O or polling of web services Concurrent requests against a local storage Updating many rows of a local storage Dividing tasks among multiple workers Image processing Image synthesize Analyzing video or audio data Processing large data sets
- 22. jQuery Plug-in In Firefox, It can be sent the complex data via postMessage() In Chrome and Safari, It will handle only a string or other simple data via postMessage() Web Workers with jQuery Hive Worker-to-worker direct messaging Object, array, and String manipulation Query JSON with JSONPath Variable evaluation and logic control flow utilities A syntax that jQuery developers will understand
- 23. Conclusion Demo Demo 1 Demo 2 Demo 3 Q&A
Editor's Notes
- #2: {}