[WWDC 21]Detect and diagnose memory issues 笔记

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概述

本Session主要解释了App内存由哪些部分组成，并介绍了可以使用Performace XCTests工具对内存问题进行排查、分析

Impact of Memory footprint

好的内存管理可以提升用户体验，可以表现在

Faster application activation，因为内存控制的好，所以app进入后台时不易被系统终止，重新激活回到前台时也更快
Responsive experience，更高的响应速度
Complex workflows，内存控制的好则意味着可以增加更多更消耗内存的功能
Wider device compatibility，控制好内存则可以兼容到更老的机器

Memory footprint

本小节主要介绍Memory footprint都是有哪些内容组成

Dirty memory consists of memory written by your application.It also includes all heap allocations such as when you use malloc, decoded image buffers,and frameworks.

Compressed memory refers to any dirty pages that haven't recently been accessed that the memory compressor has compressed.These pages will be decompressed on access.

Tools for profiling memory

Performance XCTests

可以使用XCTests去检查各个功能的性能表现，比如

Memory utilization，内存利用情况
CPU usage
Disk writes
Hitch rate，卡顿率
Wall clock time，功能的耗时情况
Application launch time

Memory utilization 示例

scss 复制代码

func testSaveMeal() {
    let app = XCUIApplication()
    let options = XCTMeasureOptions()
    options.invocationOptions = [.manuallyStart]
    measure(metrics: [XCTMemoryMetric(application: aapp)1
        options: options) {
        app.launch()
        startMeasuring()
        app.cells.firstMatch.buttons["Save meal"].firstMatch.tap()
        let savedButton = app.cells.firstMatch.buttons["Saved"].firstMatch
        XCTAssertTrue (savedButton.waitForExistendce(timeout: 30)
    }
}

上述代码检测的是点击"Save meal"按钮后内存的变化情况，变化情况如下图所示：