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Communications of the ACM


Idle-Time Garbage-Collection Scheduling

Idle-Time Garbage- Collection Scheduling, illustration

Credit: Iwona Usakiewicz / Andrij Borys Associates, Icon Google / The Chromium Projects

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Google's Chrome web browser strives to deliver a smooth user experience. An animation will update the screen at 60FPS (frames per second), giving Chrome approximately 16.6 milliseconds to perform the update. Within these 16.6ms, all input events have to be processed, all animations have to be performed, and finally the frame has to be rendered. A missed deadline will result in dropped frames. These are visible to the user and degrade the user experience. Such sporadic animation artifacts are referred to here as jank.3

JavaScript, the lingua franca of the Web, is typically used to animate Web pages. It is a garbage-collected programming language where the application developer does not have to worry about memory management. The garbage collector interrupts the application to pass over the memory allocated by the application, determine live memory, free dead memory, and compact memory by moving objects closer together. While some of these garbage-collection phases can be performed in parallel or concurrently to the application, others cannot, and as a result they may cause application pauses at unpredictable times. Such pauses may result in user-visible jank or dropped frames; therefore, we go to great lengths to avoid such pauses when animating Web pages in Chrome.


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