OK,从现在开始，我们会一个要点一个要点的把Android目前在开发上比较中要的几个知识点从源码开始详细分析，当然，在这里，我主要的是分析framework层下的代码,今天我给分析是关于ActivityManagerService.java这个类，分析内容主要为其内部原理，由于本类代码比较多，所以我不可能在一个篇幅中全部给细细分析与展示出来，所以我主要分析其内部原理：
好了先看下面:
package com.android.server.am;
18
19 import com.android.internal.R;
20 import com.android.internal.os.BatteryStatsImpl;
21 import com.android.internal.os.ProcessStats;
22 import com.android.server.AttributeCache;
23 import com.android.server.IntentResolver;
24 import com.android.server.ProcessMap;
25 import com.android.server.SystemServer;
26 import com.android.server.Watchdog;
27 import com.android.server.am.ActivityStack.ActivityState;
28 import com.android.server.wm.WindowManagerService;
30 import dalvik.system.Zygote;
32 import android.app.Activity;
33 import android.app.ActivityManager;
34 import android.app.ActivityManagerNative;
35 import android.app.ActivityThread;
36 import android.app.AlertDialog;
37 import android.app.AppGlobals;
38 import android.app.ApplicationErrorReport;
39 import android.app.Dialog;
40 import android.app.IActivityController;
41 import android.app.IActivityWatcher;
42 import android.app.IApplicationThread;
43 import android.app.IInstrumentationWatcher;
44 import android.app.INotificationManager;
45 import android.app.IProcessObserver;
46 import android.app.IServiceConnection;
47 import android.app.IThumbnailReceiver;
48 import android.app.Instrumentation;
49 import android.app.Notification;
50 import android.app.NotificationManager;
51 import android.app.PendingIntent;
52import android.app.Service;
53 import android.app.backup.IBackupManager;
54 import android.content.ActivityNotFoundException;
55 import android.content.BroadcastReceiver;
56 import android.content.ComponentCallbacks2;
57 import android.content.ComponentName;
58 import android.content.ContentResolver;
59 import android.content.Context;
60 import android.content.DialogInterface;
61 import android.content.Intent;
62 import android.content.IntentFilter;
63 import android.content.IIntentReceiver;
64 import android.content.IIntentSender;
65 import android.content.IntentSender;
66 import android.content.pm.ActivityInfo;
67 import android.content.pm.ApplicationInfo;
68 import android.content.pm.ConfigurationInfo;
69 import android.content.pm.IPackageDataObserver;
70 import android.content.pm.IPackageManager;
71 import android.content.pm.InstrumentationInfo;
72 import android.content.pm.PackageInfo;
73 import android.content.pm.PackageManager;
74 import android.content.pm.PathPermission;
75 import android.content.pm.ProviderInfo;
76 import android.content.pm.ResolveInfo;
77 import android.content.pm.ServiceInfo;
78 import android.content.pm.PackageManager.NameNotFoundException;
79 import android.content.res.CompatibilityInfo;
80 import android.content.res.Configuration;
81 import android.graphics.Bitmap;
82 import android.net.Proxy;
83 import android.net.ProxyProperties;
84 import android.net.Uri;
85 import android.os.Binder;
86 import android.os.Build;
87 import android.os.Bundle;
88 import android.os.Debug;
89 import android.os.DropBoxManager;
90 import android.os.Environment;
91 import android.os.FileObserver;
92 import android.os.FileUtils;
93 import android.os.Handler;
94 import android.os.IBinder;
95 import android.os.IPermissionController;
96 import android.os.Looper;
97 import android.os.Message;
98 import android.os.Parcel;
99 import android.os.ParcelFileDescriptor;
100 import android.os.Process;
101 import android.os.RemoteCallbackList;
102 import android.os.RemoteException;
103 import android.os.ServiceManager;
104 import android.os.StrictMode;
105 import android.os.SystemClock;
106 import android.os.SystemProperties;
107 import android.provider.Settings;
108 import android.text.format.Time;
109 import android.util.EventLog;
110 import android.util.Pair;
111 import android.util.Slog;
112 import android.util.Log;
113 import android.util.PrintWriterPrinter;
114 import android.util.SparseArray;
115 import android.util.TimeUtils;
116 import android.view.Gravity;
117 import android.view.LayoutInflater;
118 import android.view.View;
119 import android.view.WindowManager;
120 import android.view.WindowManagerPolicy;
121
122 import java.io.BufferedInputStream;
123 import java.io.BufferedOutputStream;
124 import java.io.BufferedReader;
125 import java.io.DataInputStream;
126 import java.io.DataOutputStream;
127 import java.io.File;
128 import java.io.FileDescriptor;
129 import java.io.FileInputStream;
91 import android.os.FileObserver;
92 import android.os.FileUtils;
93 import android.os.Handler;
94 import android.os.IBinder;
95 import android.os.IPermissionController;
96 import android.os.Looper;
97 import android.os.Message;
98 import android.os.Parcel;
99 import android.os.ParcelFileDescriptor;
100 import android.os.Process;
101 import android.os.RemoteCallbackList;
102 import android.os.RemoteException;
103 import android.os.ServiceManager;
104 import android.os.StrictMode;
105 import android.os.SystemClock;
106 import android.os.SystemProperties;
107 import android.provider.Settings;
108 import android.text.format.Time;
109 import android.util.EventLog;
110 import android.util.Pair;
111 import android.util.Slog;
112 import android.util.Log;
113 import android.util.PrintWriterPrinter;
114 import android.util.SparseArray;
115 import android.util.TimeUtils;
116 import android.view.Gravity;
117 import android.view.LayoutInflater;
118 import android.view.View;
119 import android.view.WindowManager;
120 import android.view.WindowManagerPolicy;
121
122 import java.io.BufferedInputStream;
123 import java.io.BufferedOutputStream;
124 import java.io.BufferedReader;
125 import java.io.DataInputStream;
126 import java.io.DataOutputStream;
127 import java.io.File;
128 import java.io.FileDescriptor;
129 import java.io.FileInputStream;
根据上面，就可以看出，此类在是server层下的，当然，也是属于framework层下的，上面导入来哪些类来实现呢，从导入的情况可以发现有电池状态实现(BatteryStatesImpl)，R,进程状态(ProcessState)，属性缓存(AttributeCache)，意图接收(IntentResolver)，进程哈系(ProcessMap)，系统服务(SystemService)，观察狗(WatchDog)，Activity栈状态(ActivityState)，窗口管理服务(WindowManagerService)，卵化器(Zygote)，Activity,Activity管理(ActivityManager)，Activity管理本地类(ActivityManagerNative)，Activity线程(ActivityThread)，警告对话框(AlertDialog)，App全局(AppGlobals)，应用错误报告(ApplicationErrorReport)，对话框(Dialog)，Activity控制接口(IActivityController)，Activity观察接口(IActivityWather)，应用线程接口(IApplicationThread),仪器观察接口(IStrumentationObserver)，通知管理接口(INotificationManager)，进程关注接口(IProcessObserver)，服务链接接口(IServerConnection)，缩略图接收器接口(IThumbnailReceiver)，仪器(Instrumentation)，通知(Notification)，通知管理(NotificationManager)，有待意图(PindingINtent)，服务(Service),备份管理接口(IBackupManager),Activity没有找到异常(ActivityNotFoundException),广播接收者(BroadcastReceiver),组建回调2(ComponentCallbacks2),组建名称(ComponentName),内容分解(ContentResolver),上下文(Context),对话框接口(DialogInterface),意图(Intent),意图过滤器(IntentFilter),意图接收接口(IIntentReceiver),意图发送接口(IIntentSender),意图发送(IntentSender),Activity信息(ActivityInfo),应用信息(ApplicationInfo),配置信息(ConfigurationInfo),包数据关注接口(IPackageDataObserver),包管理接口(IPackageManager),仪器信息(InstrmatationInfo),包信息(PackageInfo),包管理(PackageManager),路径权限(PathPermission),提供者信息(ProviderInfo),解析器信息(ResolveInfo),服务信息(ServiceInfo),名称没有发现异常(NameNotFoundException),兼容性信息(CompatibilityInfo),配置(Configuration),位图(Bitmap),代理(Proxy),代理属性(ProxyProperties),统一资源标志符(Uri),帮第器(binder),建立(Build),捆(Bundle),调试(Debug),下拉框管理器(DropBoxManager),环境变量(Environment),文件关注(FileObserver),文件单元(FileUtils),处理器(Handler),捆绑器接口(IBinder),权限控制接口(IPermissionController),论寻(Looper),消息(Message),邮包(Parcel),邮包文件描述(ParcelFileDescript),进程(Process),远程回调列表(RemoteCallBackList),远程异常(RemoteException),服务管理(ServiceManager),严格模式(StrictMode),SystemClock(系统时钟),系统属性(SystemProperties),设置(Settings),时间(Time),事件日志(EventLog),一对(Pair),系统日志(SLog),日志(Log),输入打印(PrintWriterPrinter),数组解析(ParseArray),时间单元(TImeUtils),重力(Gravity),布局填充(LayoutInfalter),视图(View),窗口管理(WindowManager),窗口管理策略(WindowManagerPolicy),输入流缓冲(BufferedInputStream)，输出流缓冲(BufferedOutputStream),缓冲读取(BufferedReader),数据输入流(DataInputStream),数据输出流(DataOutputStream),文件(File),文件描述(FileDescriptor),文件输入流(FileInputStream),文件没有发现异常(FileNotFoundException),文件输出流(FileOutputStream),IO异常(IOException),读取输入流(InputStreamReader),输入打印(PrintWriter),字符串写入(StringWriter)，非状态异常(IllegalStateException),弱引用(WeakReference),数组列表(ArrayList),集合(Collections),比较(Comparator),哈系映射(HashMap),哈系集合(HashSet),迭代(Iterator),列表(List),语言环境(Locale),映射(Map),集合(Set),原子布尔(AtomicBoolean),原子长(AtimicLong).
OK,以上就是需要导入的相关类，可能有的人看到这里就有点晕了，其实际你看到这里并能很清晰的知道相干类的话，那说明你真的很懂了，毕竟这个类是一个重量级的类，容量达到了608k,代码标准行数达到来14382行，看看上面导入的类就知道这个类不可忽视，好来我们知道了上面，现在来具体分析下它的内部运行原理吧，在这里需要注意：
public class ActivityManagerService extends ActivityManagerNative implements Watchdog.Monitor,BatteryStatesImpl.BatteryCallBack{},这里它继承了本地窗口管理类，并且同时实现了观察狗的监听器与电池状态的实现回调，接下来，看首先声明的一些相关变量：
static final String TAG = “ActivityManager”;
154 static final boolean DEBUG = false;
155 static final boolean localLOGV = DEBUG;
156 static final boolean DEBUG_SWITCH = localLOGV || false;
157 static final boolean DEBUG_TASKS = localLOGV || false;
158 static final boolean DEBUG_PAUSE = localLOGV || false;
159 static final boolean DEBUG_OOM_ADJ = localLOGV || false;
160 static final boolean DEBUG_TRANSITION = localLOGV || false;
161 static final boolean DEBUG_BROADCAST = localLOGV || false;
162 static final boolean DEBUG_BROADCAST_LIGHT = DEBUG_BROADCAST || false;
163 static final boolean DEBUG_SERVICE = localLOGV || false;
164 static final boolean DEBUG_SERVICE_EXECUTING = localLOGV || false;
165 static final boolean DEBUG_VISBILITY = localLOGV || false;
166 static final boolean DEBUG_PROCESSES = localLOGV || false;
167 static final boolean DEBUG_PROVIDER = localLOGV || false;
168 static final boolean DEBUG_URI_PERMISSION = localLOGV || false;
169 static final boolean DEBUG_USER_LEAVING = localLOGV || false;
170 static final boolean DEBUG_RESULTS = localLOGV || false;
171 static final boolean DEBUG_BACKUP = localLOGV || false;
172 static final boolean DEBUG_CONFIGURATION = localLOGV || false;
173 static final boolean DEBUG_POWER = localLOGV || false;
174 static final boolean DEBUG_POWER_QUICK = DEBUG_POWER || false;
175 static final boolean VALIDATE_TOKENS = false;
176 static final boolean SHOW_ACTIVITY_START_TIME = true;
177
178 // Control over CPU and battery monitoring.
179 static final long BATTERY_STATS_TIME = 30*60*1000; // write battery stats every 30 minutes.
180 static final boolean MONITOR_CPU_USAGE = true;
181 static final long MONITOR_CPU_MIN_TIME = 5*1000; // don’t sample cpu less than every 5 seconds.
182 static final long MONITOR_CPU_MAX_TIME = 0x0fffffff; // wait possibly forever for next cpu sample.
183 static final boolean MONITOR_THREAD_CPU_USAGE = false;
// The flags that are set for all calls we make to the package manager.
186 static final int STOCK_PM_FLAGS = PackageManager.GET_SHARED_LIBRARY_FILES;
187
188 private static final String SYSTEM_DEBUGGABLE = “ro.debuggable”;
189
190 static final boolean IS_USER_BUILD = “user”.equals(Build.TYPE);
191
192 // Maximum number of recent tasks that we can remember.
193 static final int MAX_RECENT_TASKS = 20;
194
195 // Amount of time after a call to stopAppSwitches() during which we will
196 // prevent further untrusted switches from happening.
197 static final long APP_SWITCH_DELAY_TIME = 5*1000;
198
199 // How long we wait for a launched process to attach to the activity manager
200 // before we decide it’s never going to come up for real.
201 static final int PROC_START_TIMEOUT = 10*1000;
202
203 // How long we wait for a launched process to attach to the activity manager
204 // before we decide it’s never going to come up for real, when the process was
205 // started with a wrapper for instrumentation (such as Valgrind) because it
206 // could take much longer than usual.
207 static final int PROC_START_TIMEOUT_WITH_WRAPPER = 300*1000;
208
209 // How long to wait after going idle before forcing apps to GC.
210 static final int GC_TIMEOUT = 5*1000;
211
212 // The minimum amount of time between successive GC requests for a process.
213 static final int GC_MIN_INTERVAL = 60*1000;
214
215 // The rate at which we check for apps using excessive power — 15 mins.
216 static final int POWER_CHECK_DELAY = (DEBUG_POWER_QUICK ? 2 : 15) * 60*1000;
217
218 // The minimum sample duration we will allow before deciding we have
219 // enough data on wake locks to start killing things.
220 static final int WAKE_LOCK_MIN_CHECK_DURATION = (DEBUG_POWER_QUICK ? 1 : 5) * 60*1000;
// The minimum sample duration we will allow before deciding we have
223 // enough data on CPU usage to start killing things.
224 static final int CPU_MIN_CHECK_DURATION = (DEBUG_POWER_QUICK ? 1 : 5) * 60*1000;
225
226 // How long we allow a receiver to run before giving up on it.
227 static final int BROADCAST_TIMEOUT = 10*1000;
228
229 // How long we wait for a service to finish executing.
230 static final int SERVICE_TIMEOUT = 20*1000;
231
232 // How long a service needs to be running until restarting its process
233 // is no longer considered to be a relaunch of the service.
234 static final int SERVICE_RESTART_DURATION = 5*1000;
235
236 // How long a service needs to be running until it will start back at
237 // SERVICE_RESTART_DURATION after being killed.
238 static final int SERVICE_RESET_RUN_DURATION = 60*1000;
239
240 // Multiplying factor to increase restart duration time by, for each time
241 // a service is killed before it has run for SERVICE_RESET_RUN_DURATION.
242 static final int SERVICE_RESTART_DURATION_FACTOR = 4;
243
244 // The minimum amount of time between restarting services that we allow.
245 // That is, when multiple services are restarting, we won’t allow each
246 // to restart less than this amount of time from the last one.
247 static final int SERVICE_MIN_RESTART_TIME_BETWEEN = 10*1000;
248
249 // Maximum amount of time for there to be no activity on a service before
250 // we consider it non-essential and allow its process to go on the
251 // LRU background list.
252 static final int MAX_SERVICE_INACTIVITY = 30*60*1000;
253
254 // How long we wait until we timeout on key dispatching.
255 static final int KEY_DISPATCHING_TIMEOUT = 5*1000;
// How long we wait until we timeout on key dispatching during instrumentation.
258 static final int INSTRUMENTATION_KEY_DISPATCHING_TIMEOUT = 60*1000;
259
260 static final int MY_PID = Process.myPid();
261
262 static final String[] EMPTY_STRING_ARRAY = new String[0];
263
264 public ActivityStack mMainStack;
上面是相关的一些前奏变量声明，看声明良不小哦，毕竟ActivityManagerService为Android内核的三大核心功能之一，Android内核的三大核心功能分别是:ActivityManagerService,WindowManagerService,View. 我从功能的角度可以知道ActivityManagerService主要有三大功能，即对应用程序的Activity作统一调度，内存管理与进程管理这三大主要功能，我们分析下，应用程序需要运行Activity,首先会通过ActivityManagerService来决定是否启动该Activity,再就是Activity退出后，所在的进程并不会立即被杀死，而会短时间存活在内存里，以便在下次启动时来提升其速度，当然在内存紧张时会对其杀死，这是由ActivityManagerService来完成的，应用程序并不需要对其管理，再就是进程管理，对其进程运行的API信息进行查询。
下面我们就单一来讲下，Activity调度：
思路：对其应用要启动的Activity必须通过ActivityManagerService来对记录的指示启动，当遇到其Activity停止或者启动需求时，它都会对其记录进行更新，从而掌握了Activity的启动与否的状态信息，在这里顺便来举一个Activity启动的几种方式:一般有四种：1.可在应用程序中调用this.startActivity()来启动指定的Activity,2.在Home程序中单击一个图标来启动新的Activity,3.按”Back(回退键)”来结束当前Activity,从而自动启动上一个Activity,4.长按Home键，显示出当前列表，从中选择一个启动。从上面可知，启动可分为顺序启动与前端处理启动，后面三种分为前端处理启动，看来要讲的还很多，今天就讲到这里吧，明天继续。。。
