{"id":22564,"date":"2026-02-20T18:16:10","date_gmt":"2026-02-20T09:16:10","guid":{"rendered":"https:\/\/aireviewirush.com\/?p=22564"},"modified":"2026-02-20T18:16:11","modified_gmt":"2026-02-20T09:16:11","slug":"android-builders-weblog-below-the-hood-android-17s-lock-free-messagequeue","status":"publish","type":"post","link":"https:\/\/aireviewirush.com\/?p=22564","title":{"rendered":"Android Builders Weblog: Below the hood: Android 17\u2019s lock-free MessageQueue"},"content":{"rendered":"


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\nPosted by Shai Barack, Android Platform Efficiency Lead and Charles Munger, Principal Software program Engineer<\/i><\/p>\n
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In Android 17, apps focusing on SDK 37 or increased will obtain a brand new implementation of MessageQueue the place the implementation is lock-free. The brand new implementation improves efficiency and reduces missed frames, however might break purchasers that mirror on MessageQueue personal fields and strategies. To be taught extra concerning the conduct change and how one can mitigate affect, <\/span>try the MessageQueue conduct change documentation<\/span><\/a>. This technical weblog put up gives an summary of the MessageQueue rearchitecture and how one can analyze lock competition points utilizing Perfetto.<\/span><\/p>\n

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The <\/span>Looper<\/span><\/a> drives the UI thread of each Android utility. It pulls work from a <\/span>MessageQueue<\/span><\/a>, dispatches it to a <\/span>Handler<\/span><\/a>, and repeats. For twenty years, <\/span><\/span>MessageQueue<\/span> used a single monitor lock (i.e. a <\/span><\/span>synchronized<\/span> <\/span>code block) to guard its state.<\/span><\/span><\/span><\/p>\n

Android 17 introduces a major replace to this part: a lock-free implementation named <\/span>DeliQueue<\/span>.<\/span><\/span><\/p>\n

This put up explains how locks have an effect on UI efficiency, the way to analyze these points with Perfetto, and the particular algorithms and optimizations used to enhance the Android fundamental thread.<\/span><\/span><\/p>\n

The issue: Lock Rivalry and Precedence Inversion<\/span><\/span><\/span><\/p>\n

The legacy <\/span><\/span>MessageQueue<\/span> <\/span>functioned as a precedence queue protected by a single lock. If a background thread posts a message whereas the principle thread performs queue upkeep, the background thread blocks the principle thread.<\/span><\/span><\/p>\n

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When two or extra threads are competing for unique use of the identical lock, that is referred to as <\/span>Lock competition<\/span>. This competition could cause\u00a0<\/span>Precedence Inversion<\/span>, resulting in UI jank and different efficiency issues.<\/span><\/span><\/p>\n

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Precedence inversion can occur when a high-priority thread (just like the UI thread) is made to attend for a low-priority thread. Take into account this sequence:<\/span><\/span><\/p>\n

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  1. \n

    A <\/span>low precedence<\/span> background thread acquires the<\/span><\/span> <\/span>MessageQueue<\/span> <\/span>lock to put up the results of work that it did.<\/span><\/span><\/p>\n<\/li>\n

  2. \n

    A <\/span>medium precedence<\/span> thread turns into runnable and the Kernel’s scheduler allocates it CPU time, preempting the low precedence thread.<\/span><\/span><\/p>\n<\/li>\n

  3. \n

    The <\/span>excessive precedence<\/span> UI thread finishes its present process and makes an attempt to learn from the queue, however is blocked as a result of the low precedence thread holds the lock.<\/span><\/span><\/p>\n<\/li>\n<\/ol>\n

    The low-priority thread blocks the UI thread, and the medium-priority work delays it additional.<\/span><\/span><\/p>\n

    \"A<\/span><\/span><\/span><\/div>\n

    Analyzing competition with Perfetto<\/span><\/span><\/span><\/span><\/p>\n

    You’ll be able to diagnose these points utilizing <\/span>Perfetto<\/span><\/a>. In a typical hint, a thread blocked on a monitor lock enters the sleeping state, and Perfetto exhibits a slice indicating the lock proprietor.<\/span><\/span><\/p>\n

    Whenever you question hint information, search for slices named \u201cmonitor competition with \u2026\u201d adopted by the title of the thread that owns the lock and the code website the place the lock was acquired.<\/span><\/span><\/p>\n

    Case research: Launcher jank<\/span><\/span><\/span><\/span><\/p>\n

    As an example, let\u2019s analyze a hint the place a consumer skilled jank whereas navigating dwelling on a Pixel cellphone instantly after taking a photograph within the digital camera app. Under we see a screenshot of Perfetto displaying the occasions main as much as the missed body:<\/span><\/span><\/p>\n

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    \"A<\/span><\/span><\/div>\n

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