1、概览 ServiceRecord首先针对intent，维护一个IntentBindRecord map; 在IntentBindRecord中又针对ProcessRecord，维护一个AppBindRecord的map ; 在AppBindRecord中维护一个ConnectionRecord的集合。
主要结构如下图 2、细节 1）ConnectionRecord 描述单个service的绑定，持有上一级AppBindRecord的引用，对应客户端的ServiceConnection
final AppBindRecord binding; // The application/service binding.添加connection : bindServiceLocked
移除connection : removeConnectionLocked，具体见 2）中代码
2）AppBindRecord 描述一个Service与Client application的关联
final ServiceRecord service; // The running service. final IntentBindRecord intent; // The intent we are bound to. final ProcessRecord client; // Who has started/bound the service. final ArraySet<ConnectionRecord> connections = new ArraySet<>(); // All ConnectionRecord for this client. 添加app: retrieveAppBindingLocked 根据intent找到对应的IntentBindRecord，再根据ProcessRecord在IntentBindRecord中找对应的AppBindRecord，存在则返回，不存在则创建 public AppBindRecord retrieveAppBindingLocked(Intent intent, ProcessRecord app) { Intent.FilterComparison filter = new Intent.FilterComparison(intent); IntentBindRecord i = bindings.get(filter); if (i == null) { i = new IntentBindRecord(this, filter); bindings.put(filter, i); } AppBindRecord a = i.apps.get(app); if (a != null) { return a; } a = new AppBindRecord(this, i, app); i.apps.put(app, a); return a; } 移除app: removeConnectionLocked 先从AppBindRecord移除当前ConnectionRecord，若移除完后connections 集合为空，则从对应的IntentBindRecord中移除当前AppBindRecord void removeConnectionLocked(ConnectionRecord c, ProcessRecord skipApp, ActivityServiceConnectionsHolder skipAct) { IBinder binder = c.conn.asBinder(); AppBindRecord b = c.binding; ...... if (b.connections.size() == 0) { b.intent.apps.remove(b.client); } }3）IntentBindRecord 绑定到Service的特定Intent
/** All apps that have bound to this Intent. */ final ArrayMap<ProcessRecord, AppBindRecord> apps = new ArrayMap<ProcessRecord, AppBindRecord>(); 添加binding: retrieveAppBindingLocked 根据intent找到对应的IntentBindRecord，若不存在则创建，并添加到ServiceRecord的bindings map中移除binding Service销毁时clear4）ServiceRecord 对应于App的Service
final ArrayMap<Intent.FilterComparison, IntentBindRecord> bindings = new ArrayMap<Intent.FilterComparison, IntentBindRecord>(); // All active bindings to the service，代表bind 这个service的链接 private final ArrayMap<IBinder, ArrayList<ConnectionRecord>> connections = new ArrayMap<IBinder, ArrayList<ConnectionRecord>>();1、BIND_TREAT_LIKE_ACTIVITY 将binding 视为持有一个activity，unbinding视为activity在后台。这意味着unbinding时，进程将会进入activity的LRU list而不是常规的LRU list，从而更有可能保持这个进程。这个通常用在输入法进程，以便更快捷的切换键盘。
需要校验calling MANAGE_ACTIVITY_STACKS 权限
if ((flags&Context.BIND_TREAT_LIKE_ACTIVITY) != 0) { s.app.treatLikeActivity = true; } // This could have made the service more important. mAm.updateLruProcessLocked(s.app, (callerApp.hasActivitiesOrRecentTasks() && s.app.hasClientActivities()) || (callerApp.getCurProcState() <= ActivityManager.PROCESS_STATE_TOP && (flags & Context.BIND_TREAT_LIKE_ACTIVITY) != 0), b.client);2、BIND_SCHEDULE_LIKE_TOP_APP 此标志仅用于系统调整IME（以及与top应用程序紧密配合的任何进程外用户可见组件）的调度策略。所以托管此类服务的UI能够拥有top app一样的调度策略
仅限于系统调用，否则会抛出安全异常
3、BIND_ALLOW_WHITELIST_MANAGEMENT 允许绑定Service应用程序管理白名单，例如临时绕过省电模式
仅限于系统调用，否则会抛出安全异常
if ((c.flags&Context.BIND_ALLOW_WHITELIST_MANAGEMENT) != 0) { s.whitelistManager = true; } // If this connection requested whitelist management, see if we should // now clear that state. if ((c.flags&Context.BIND_ALLOW_WHITELIST_MANAGEMENT) != 0) { s.updateWhitelistManager(); if (!s.whitelistManager && s.app != null) { updateWhitelistManagerLocked(s.app); } }4、BIND_ALLOW_BACKGROUND_ACTIVITY_STARTS 允许绑定Service的进程启动后台Activity，需要校验android.Manifest.permission#START_ACTIVITIES_FROM_BACKGROUND
5、BIND_EXTERNAL_SERVICE 这将 Service绑定到调用的应用package中，而非声明Service的package，即Service将在调用者进程package和userId下运行。
1）Service的声明需要以下几点，以下三个属性皆必须为true
<service android:name=".XXXService" android:exported="true" android:externalService="true" android:isolatedProcess="true" />2）绑定Service需要加入这个flag
bindService(intent, mConnection, Context.BIND_AUTO_CREATE | Context.BIND_EXTERNAL_SERVICE);涉及到的校验代码在retrieveServiceLocked中
