Android Uid,UserId,AppId,Pid

1、Uid

android中uid用于标识一个应用程序，uid在应用安装时被分配，并且在应用存在于手机上期间，都不会改变，范围是从10000开始，到19999结束,而且，UID由用户ID(UserId)和应用ID(AppId)共同决定

1.1、Uid来源(android 9.0)

frameworks/base/core/java/android/os/UserHandle.java

/**
* @hide Range of uids allocated for a user.
*/
public static final int PER_USER_RANGE = 100000;

/**
* Returns the uid that is composed from the userId and the appId.
* @hide
*/
public static int getUid(@UserIdInt int userId, @AppIdInt int appId) {
    if (MU_ENABLED) {
    //默认不创建多个用户时，android 只有一个用户，uid==aapId
        eturn userId * PER_USER_RANGE + (appId % PER_USER_RANGE);
    } else {
       return appId;
 }      

1.2、查看Uid

方式1：abd shell cat data/system/packages.xml，里面包含所有应用的uid和一些有关其的信息（需要root）
方式2：adb shell dumpsys package 应用包名 | adb shell grep userId=
方式3：adb shell cat /proc//status | adb shell grep Uid
1、adb shell ps -A | adb shell grep -r “com.example.testpor”（-A:高android版本的adb shell需要带-A参数）,其中，第二列30209就是pid

octopus-n106:/ # ps  | grep -r "com.example.testpor"
(standard input):u0_a65    30209 1662  1006360 48836    ep_poll aae7b2d8 S com.example.testpor

2、adb shell cat /proc/30209 /status | grep Uid

Uid:    10065   10065   10065   10065

2、UserId

系统中会有多个用户 (User，即手机里的主机、访客等多用户), 每个用户也有一个唯一的 ID 值, 称为"UserId"

3、AppId

一个进程的appId是固定的，在初始化或安装的时候就决定了
frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java

10170    private void commitScanResultsLocked(@NonNull ScanRequest request, @NonNull ScanResult result)
10171            throws PackageManagerException {
			....	
10184
10185        if (newPkgSettingCreated) {
10186            if (originalPkgSetting != null) {
10187                mSettings.addRenamedPackageLPw(pkg.packageName, originalPkgSetting.name);
10188            }
10189            // THROWS: when we can't allocate a user id. add call to check if there's
10190            // enough space to ensure we won't throw; otherwise, don't modify state
10191            mSettings.addUserToSettingLPw(pkgSetting);
10192
10193            if (originalPkgSetting != null && (scanFlags & SCAN_CHECK_ONLY) == 0) {
10194                mTransferedPackages.add(originalPkgSetting.name);
10195            }
10196        }

frameworks/base/services/core/java/com/android/server/pm/Settings.java

882    void addUserToSettingLPw(PackageSetting p) throws PackageManagerException {
883        if (p.appId == 0) {
884            // Assign new user ID
885            p.appId = newUserIdLPw(p);
886        } else {
887            // Add new setting to list of user IDs
888            addUserIdLPw(p.appId, p, p.name);
889        }
890        if (p.appId < 0) {
891            PackageManagerService.reportSettingsProblem(Log.WARN,
892                    "Package " + p.name + " could not be assigned a valid UID");
893            throw new PackageManagerException(INSTALL_FAILED_INSUFFICIENT_STORAGE,
894                    "Package " + p.name + " could not be assigned a valid UID");
895        }
896    }

4213    private int newUserIdLPw(Object obj) {
4214        // Let's be stupidly inefficient for now...
4215        final int N = mUserIds.size();
4216        for (int i = mFirstAvailableUid; i < N; i++) {
4217            if (mUserIds.get(i) == null) {
4218                mUserIds.set(i, obj);
4219                return Process.FIRST_APPLICATION_UID + i;
4220            }
4221        }
4222
4223        // None left?
4224        if (N > (Process.LAST_APPLICATION_UID-Process.FIRST_APPLICATION_UID)) {
4225            return -1;
4226        }
4227
4228        mUserIds.add(obj);
4229        return Process.FIRST_APPLICATION_UID + N;
4230    }

4、Pid

Pid就是各进程的身份标识,程序一运行系统就会自动分配给进程一个独一无二的PID。进程中止后PID被系统回收，可能会被继续分配给新运行的程序，但是在android系统中一般不会把已经kill掉的进程ID重新分配给新的进程，新产生进程的进程号，一般比产生之前所有的进程号都要大。