一、Logcat

二、Dumpsys

C:\Users\pengcheng.ding>adb shell dumpsys --help
usage: dumpsys
         To dump all services.
or:
       dumpsys [-t TIMEOUT] [--priority LEVEL] [--clients] [--dump] [--pid] [--thread] [--help | -l | --skip SERVICES | SERVICE [ARGS]]
         --help: shows this help
         -l: only list services, do not dump them
         -t TIMEOUT_SEC: TIMEOUT to use in seconds instead of default 10 seconds
         -T TIMEOUT_MS: TIMEOUT to use in milliseconds instead of default 10 seconds
         --clients: dump client PIDs instead of usual dump
         --dump: ask the service to dump itself (this is the default)
         --pid: dump PID instead of usual dump
         --proto: filter services that support dumping data in proto format. Dumps
               will be in proto format.
         --priority LEVEL: filter services based on specified priority
               LEVEL must be one of CRITICAL | HIGH | NORMAL
         --skip SERVICES: dumps all services but SERVICES (comma-separated list)
         --stability: dump binder stability information instead of usual dump
         --thread: dump thread usage instead of usual dump
         SERVICE [ARGS]: dumps only service SERVICE, optionally passing ARGS to it

dumpsys基本命令如上，adb shell dumpsys xxx，其中xxx通常为android servicemanager里面注册的服务，只要adb shell dumpsys -l能输出的服务都可以通过此命令来dumpsys一些关键信息。如下依次来介绍dumpsys实现原理。

1、dumpsys进程

//frameworks/native/cmds/dumpsys/Android.bp
cc_binary {
    name: "dumpsys",
    defaults: ["dumpsys_defaults"],
    srcs: [ "main.cpp", ],
    shared_libs: [ "packagemanager_aidl-cpp", ],
}
cc_defaults {
    name: "dumpsys_defaults",
    cflags: [ "-Wall",  "-Werror", ],
    srcs: [ "dumpsys.cpp", ],
    shared_libs: [
        "libbase",
        "libutils",
        "liblog",
        "libbinder",
        "libbinderdebug",
    ],
    static_libs: [  "libserviceutils", ],
}
//frameworks/native/cmds/dumpsys/main.cpp
int main(int argc, char* const argv[]) {
    signal(SIGPIPE, SIG_IGN);
    sp<IServiceManager> sm = defaultServiceManager();
    fflush(stdout);
    if (sm == nullptr) {
        ALOGE("Unable to get default service manager!");
        std::cerr << "dumpsys: Unable to get default service manager!" << std::endl;
        return 20;
    }
    Dumpsys dumpsys(sm.get());  //核心逻辑
    return dumpsys.main(argc, argv);
}

如上代码dumpsys就是一个普通的native进程，核心的逻辑还是frameworks/native/cmds/dumpsys/dumpsys.cpp的main函数：

因此dumpsys xxx最后是通过servicemanager让系统Service进行了dump，常用的dumpsys命令如下：

adb shell dumpsys activity //查询AMS服务相关信息
adb shell dumpsys package  //查询包管理相关信息
adb shell dumpsys window   //查询WMS服务相关信息
adb shell dumpsys meminfo/cpuinfo/gfxinfo //查询内存/CPU/帧率相关信息
adb shell dumpsys power/batterystats/battery   //查询电源相关信息/电池状态/电池
adb shell dumpsys alarm/location     //查询闹钟/位置相关信息
adb shell dumpsys user/device_policy     //查询用户相关信息
adb shell dumpsys connectivity/netpolicy/netstats   //查询网络连接/策略/状态
adb shell dumpsys network_management    //查询网络管理相关信息

所有的service定义和service注册的字符串全在如下文件进行定义Context.java - OpenGrok cross reference for /frameworks/base/core/java/android/content/Context.java