APM相关

记录一下最近在扩展GT时遇到的一些问题

1. 通过residentSize获取的常驻内存和Xcode上显示的内存值不一致。
   原因大致如下：
   residentSize返回的内存由这三部分构成（DirtyMemory + CompressedMemory + CleanMemory）
   而
   Xcode统计的是MemoryFootPrint，不包含CleanMemory。

用WWDC-Memory Deep Dive中的一句话总结：

when we talk about the app's footprint, we're really talking about the dirty and compressed segments.Clean memory doesn't really count.

memoryFootPrint.png

参考：
iOS内存abort(Jetsam) 原理探究

iOS Memory Deep Dive

WWDC 2018：iOS 内存深入研究

深度揭秘各大 APM 厂商 iOS SDK 背后的核心技术和实现细节

iOS 性能监控 SDK

基于iOS平台的性能检测方案

2. GT源码中获取residentMemorySize的API已经不被Apple建议使用

源API：

- (NSUInteger)getResidentMemory
{
    struct task_basic_info t_info;
    mach_msg_type_number_t t_info_count = TASK_BASIC_INFO_COUNT;
    
    int r = task_info(mach_task_self(), TASK_BASIC_INFO, (task_info_t)&t_info, &t_info_count);
    if (r == KERN_SUCCESS)
    {
        return t_info.resident_size;
    }
    else
    {
        return -1;
    }
}

apple.png

可以更换为Apple建议的API：

- (NSUInteger)updateMemoryResidentSize {
    struct mach_task_basic_info t_info;
    mach_msg_type_number_t t_info_count = MACH_TASK_BASIC_INFO_COUNT;
    int r = task_info(mach_task_self(), MACH_TASK_BASIC_INFO, (task_info_t)&t_info, &t_info_count);
    if (r == KERN_SUCCESS) {
        return t_info.resident_size;
    } else {
        return -1;
    }
}