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POHTML5/JS - Start several webworkers
 

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    <p>I'm currently writing on a program, where I have to deal with huge arrays. I can however split those arrays. My plan now is, to process the arrays in different web workers. I have however never worked with them and do have several questions:</p> <p><strong>1.</strong> How would I run several web workers? I tried a for-loop looking like that:</p> <pre><code>for(i = 0; i &lt; eD.threads; i++){ //start workers here var worker = new Worker("js/worker/imageValues.js"); worker.postMessage(brightness, cD.pixels[i]); } </code></pre> <p>Here I do get the error, that the object couldn't be cloned. Which seems logical. I guess it would be better to save them in an Array?</p> <p><strong>2.</strong> How would I control that all have finished their work? (I need to reassembly the array and work with it later)</p> <p><strong>3.</strong> How many web workers really bring an improvement?</p> <p><strong>4.</strong> Is there any advanced tutorial, besides the MDN-entry?</p> <p>Thank you!</p>
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    1. COFor #2: You'd have to use `postMessage` from the Worker to send back a message to this parent JS saying that worker is done processing (and probably pass the results)...so you'd have to add an `onmessage` listener for each Worker, in the loop. You'd store all these responses in probably an array. When the number of responses in the array is the same as the number of workers created, that should mean all are done...and you can deal with that array you created. This could be made "cleaner" by using the concept of jQuery's deferred objects
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    2. CO"Cannot be cloned" here means that what you're *passing to* the worker couldn't be cloned. To avoid race conditions, objects are never shared between workers and the main thread. Objects must either be copied into the worker's memory space, or (with `Blob`s and typed arrays) the main thread may relinquish memory space to a worker and lose the reference to the object.
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    3. COOk. Read about it, but forgot it. Anyway. If I create a temporary variable in the loop, safe the array as a string and pass that string on, would that be a better solution? Somewhere I read, that I only send Strings to workers, somewhere else it says, that I can transfer variables? Thank you both for your explanation though, helps me to get started!
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