public void forceStopPackage(final String packageName, int userId) {

    // .. 权限检查，省略

    long callingId = Binder.clearCallingIdentity();
    try {
        IPackageManager pm = AppGlobals.getPackageManager();
        synchronized(this) {
            int[] users = userId == UserHandle.USER_ALL
                    ? mUserController.getUsers() : new int[] { userId };
            for (int user : users) {

                // 状态判断，省略..

                int pkgUid = -1;
                try {
                    pkgUid = pm.getPackageUid(packageName, MATCH_DEBUG_TRIAGED_MISSING,
                            user);
                } catch (RemoteException e) {
                }
                if (pkgUid == -1) {
                    Slog.w(TAG, "Invalid packageName: " + packageName);
                    continue;
                }
                try {
                    pm.setPackageStoppedState(packageName, true, user);
                } catch (RemoteException e) {
                } catch (IllegalArgumentException e) {
                    Slog.w(TAG, "Failed trying to unstop package "
                            + packageName + ": " + e);
                }
                if (mUserController.isUserRunning(user, 0)) {
                        // 根据 UID 和包名杀进程
                    forceStopPackageLocked(packageName, pkgUid, "from pid " + callingPid);
                    finishForceStopPackageLocked(packageName, pkgUid);
                }
            }
        }
    } finally {
        Binder.restoreCallingIdentity(callingId);
    }
}

final boolean forceStopPackageLocked(String packageName, int appId,
        boolean callerWillRestart, boolean purgeCache, boolean doit,
        boolean evenPersistent, boolean uninstalling, int userId, String reason) {
    int i;

    // .. 状态判断，省略

    boolean didSomething = mProcessList.killPackageProcessesLocked(packageName, appId, userId,
            ProcessList.INVALID_ADJ, callerWillRestart, true /* allowRestart */, doit,
            evenPersistent, true /* setRemoved */,
            packageName == null ? ("stop user " + userId) : ("stop " + packageName));

    didSomething |=
            mAtmInternal.onForceStopPackage(packageName, doit, evenPersistent, userId);

    // 清理 service
    // 清理 broadcastreceiver
    // 清理 providers
    // 清理其他

    return didSomething;
}

void kill(String reason, boolean noisy) {
    if (!killedByAm) {
        Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "kill");
        if (mService != null && (noisy || info.uid == mService.mCurOomAdjUid)) {
            mService.reportUidInfoMessageLocked(TAG,
                    "Killing " + toShortString() + " (adj " + setAdj + "): " + reason,
                    info.uid);
        }
        if (pid > 0) {
            EventLog.writeEvent(EventLogTags.AM_KILL, userId, pid, processName, setAdj, reason);
            Process.killProcessQuiet(pid);
            ProcessList.killProcessGroup(uid, pid);
        } else {
            pendingStart = false;
        }
        if (!mPersistent) {
            killed = true;
            killedByAm = true;
        }
        Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
    }
}

int killProcessGroup(uid_t uid, int initialPid, int signal) {
    return KillProcessGroup(uid, initialPid, signal, 40 /*retries*/);
}

static int KillProcessGroup(uid_t uid, int initialPid, int signal, int retries) {

    // 省略

    int retry = retries;
    int processes;
    while ((processes = DoKillProcessGroupOnce(cgroup, uid, initialPid, signal)) > 0) {
        LOG(VERBOSE) << "Killed " << processes << " processes for processgroup " << initialPid;
        if (retry > 0) {
            std::this_thread::sleep_for(5ms);
            --retry;
        } else {
            break;
        }
    }

    // 省略
}