主目录见：Android高级进阶知识（这是总目录索引）
上一篇文章注册广播接收者的源码分析我们已经讲了注册的过程，我们知道动态广播注册对应的在AMS中的节点是BroadcastFilter，静态广播是在PMS中对应的是ResolveInfo，我们这篇文章将讲另外一个过程，那就是广播的发送过程，这一过程肯定就是发送到AMS中，然后AMS查找自己注册的广播中有没有这个广播，如果有则会发送给订阅了该广播的所有接收者。
一.目标
今天介绍这篇也是跟广播相关的，其实这个过程除了多一些跨进程通讯之外，其他跟事件总线还是有点像的，至少思想类似。今天目标如下：
1.了解广播的整体流程；
2.为插件化框架做知识储备。
二.源码解析
如果看过前面源码分析的应该知道，我们的调用最终都会到达ContextImpl类中，广播也不例外，我们看到这个类中的sendBroadcast()方法：
@Override
public void sendBroadcast(Intent intent) {
warnIfCallingFromSystemProcess();
//resolvedType表示intent的MIME类型
String resolvedType = intent.resolveTypeIfNeeded(getContentResolver());
try {
//准备离开应用程序进程
intent.prepareToLeaveProcess(this);
ActivityManagerNative.getDefault().broadcastIntent(
mMainThread.getApplicationThread(), intent, resolvedType, null,
Activity.RESULT_OK, null, null, null, AppOpsManager.OP_NONE, null, false, false,
getUserId());
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
我们看到这里ActivityManagerNative#getDefault()获取到的是远程服务的代理，所以我们直接看到AMS(ActivityManagerService)的broadcastIntent()方法:
public final int broadcastIntent(IApplicationThread caller,
Intent intent, String resolvedType, IIntentReceiver resultTo,
int resultCode, String resultData, Bundle resultExtras,
String[] requiredPermissions, int appOp, Bundle bOptions,
boolean serialized, boolean sticky, int userId) {
enforceNotIsolatedCaller("broadcastIntent");
synchronized(this) {
intent = verifyBroadcastLocked(intent);
//从mLruProcesses集合中查找进程记录
final ProcessRecord callerApp = getRecordForAppLocked(caller);
final int callingPid = Binder.getCallingPid();
final int callingUid = Binder.getCallingUid();
final long origId = Binder.clearCallingIdentity();
int res = broadcastIntentLocked(callerApp,
callerApp != null ? callerApp.info.packageName : null,
intent, resolvedType, resultTo, resultCode, resultData, resultExtras,
requiredPermissions, appOp, bOptions, serialized, sticky,
callingPid, callingUid, userId);
Binder.restoreCallingIdentity(origId);
return res;
}
}
我们看到程序会调用broadcastIntentLocked()方法继续处理，接下来这个方法巨长，我们精简地看：
final int broadcastIntentLocked(ProcessRecord callerApp,
String callerPackage, Intent intent, String resolvedType,
IIntentReceiver resultTo, int resultCode, String resultData,
Bundle resultExtras, String[] requiredPermissions, int appOp, Bundle bOptions,
boolean ordered, boolean sticky, int callingPid, int callingUid, int userId) {
intent = new Intent(intent);
//1.设置这个标志说明不会发送给已经停止的app
intent.addFlags(Intent.FLAG_EXCLUDE_STOPPED_PACKAGES);
//如果你还没完成启动，那么不允许创建一个新的进程
if (!mProcessesReady && (intent.getFlags()&Intent.FLAG_RECEIVER_BOOT_UPGRADE) == 0) {
//这个标志说明只有静态注册广播能接受到广播
intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY);
}
userId = mUserController.handleIncomingUser(callingPid, callingUid, userId, true,
ALLOW_NON_FULL, "broadcast", callerPackage);
// Make sure that the user who is receiving this broadcast is running.
// If not, we will just skip it. Make an exception for shutdown broadcasts
// and upgrade steps.
//确认广播接收者已经运行起来，如果没有运行，则看是不是关闭广播和系统更新广播，不是则直接返回
if (userId != UserHandle.USER_ALL && !mUserController.isUserRunningLocked(userId, 0)) {
if ((callingUid != Process.SYSTEM_UID
|| (intent.getFlags() & Intent.FLAG_RECEIVER_BOOT_UPGRADE) == 0)
&& !Intent.ACTION_SHUTDOWN.equals(intent.getAction())) {
return ActivityManager.BROADCAST_FAILED_USER_STOPPED;
}
}
//2.检查BroadcastOptions
BroadcastOptions brOptions = null;
if (bOptions != null) {
brOptions = new BroadcastOptions(bOptions);
//获取发送广播时候，系统把cpu暂时唤醒的时间
if (brOptions.getTemporaryAppWhitelistDuration() > 0) {
//是否有添加这个应用到活动应用白名单中的权限
if (checkComponentPermission(
android.Manifest.permission.CHANGE_DEVICE_IDLE_TEMP_WHITELIST,
Binder.getCallingPid(), Binder.getCallingUid(), -1, true)
!= PackageManager.PERMISSION_GRANTED) {
String msg = "Permission Denial: " + intent.getAction()
+ " broadcast from " + callerPackage + " (pid=" + callingPid
+ ", uid=" + callingUid + ")"
+ " requires "
+ android.Manifest.permission.CHANGE_DEVICE_IDLE_TEMP_WHITELIST;
Slog.w(TAG, msg);
throw new SecurityException(msg);
}
}
}
//3.检查是否有权发送广播
final String action = intent.getAction();
final boolean isProtectedBroadcast;
try {
//到PMS中查找是否isProtectedBroadcast 是true，
//即是否在Framework/base/core/res/AndroidManifest.xml中
isProtectedBroadcast = AppGlobals.getPackageManager().isProtectedBroadcast(action);
} catch (RemoteException e) {
Slog.w(TAG, "Remote exception", e);
return ActivityManager.BROADCAST_SUCCESS;
}
final boolean isCallerSystem;
switch (UserHandle.getAppId(callingUid)) {
case Process.ROOT_UID:
case Process.SYSTEM_UID:
case Process.PHONE_UID:
case Process.BLUETOOTH_UID:
case Process.NFC_UID:
//是否是系统发送的广播
isCallerSystem = true;
break;
default:
isCallerSystem = (callerApp != null) && callerApp.persistent;
break;
}
// First line security check before anything else: stop non-system apps from
// sending protected broadcasts.
if (!isCallerSystem) {
if (isProtectedBroadcast) {
//如果不是系统进程调用，但是又在Framework/base/core/res/AndroidManifest.xml中，
//这种情况基本没有，如果存在那就是不允许的
String msg = "Permission Denial: not allowed to send broadcast "
+ action + " from pid="
+ callingPid + ", uid=" + callingUid;
Slog.w(TAG, msg);
throw new SecurityException(msg);
} else if (AppWidgetManager.ACTION_APPWIDGET_CONFIGURE.equals(action)
|| AppWidgetManager.ACTION_APPWIDGET_UPDATE.equals(action)) {
//这是历史遗留原因，系统不建议我们发送这两类广播
if (callerPackage == null) {
String msg = "Permission Denial: not allowed to send broadcast "
+ action + " from unknown caller.";
Slog.w(TAG, msg);
throw new SecurityException(msg);
} else if (intent.getComponent() != null) {
//如果发送者的包名和接收者不在一个包名下面则禁止发送
if (!intent.getComponent().getPackageName().equals(
callerPackage)) {
String msg = "Permission Denial: not allowed to send broadcast "
+ action + " to "
+ intent.getComponent().getPackageName() + " from "
+ callerPackage;
Slog.w(TAG, msg);
throw new SecurityException(msg);
}
} else {
// Limit broadcast to their own package.
intent.setPackage(callerPackage);
}
}
}
//4.省略一些系统相关广播的处理
......
//5.处理粘性广播
//6.动态广播和静态广播注册表的查询
}
从上面代码我们可以看出，我们先列出了4个步骤的讲解，首先1.标志的设置，2.检查BroadcastOptions，3.检查是否有权发送广播，4.省略一些系统相关广播的处理。然后我们还有两个步骤未讲解，我们下面分开来讲。
1.处理粘性广播
// Add to the sticky list if requested.
if (sticky) {
//检查是否有android.Manifest.permission.BROADCAST_STICKY权限
if (checkPermission(android.Manifest.permission.BROADCAST_STICKY,
callingPid, callingUid)
!= PackageManager.PERMISSION_GRANTED) {
String msg = "Permission Denial: broadcastIntent() requesting a sticky broadcast from pid="
+ callingPid + ", uid=" + callingUid
+ " requires " + android.Manifest.permission.BROADCAST_STICKY;
Slog.w(TAG, msg);
throw new SecurityException(msg);
}
//发送粘性广播不能强制添加别的权限
if (requiredPermissions != null && requiredPermissions.length > 0) {
Slog.w(TAG, "Can't broadcast sticky intent " + intent
+ " and enforce permissions " + Arrays.toString(requiredPermissions));
return ActivityManager.BROADCAST_STICKY_CANT_HAVE_PERMISSION;
}
//粘性广播不能有特定的组件名称
if (intent.getComponent() != null) {
throw new SecurityException(
"Sticky broadcasts can't target a specific component");
}
//如果用户id不是USER_ALL
if (userId != UserHandle.USER_ALL) {
//首先取出所有USER_ALL对应的粘性广播，所以为了确保不会跟发送给所有用户的广播冲突，
//这里会进行检查
ArrayMap> stickies = mStickyBroadcasts.get(
UserHandle.USER_ALL);
if (stickies != null) {
//从发送给所有用户的粘性广播中查找是否有跟发送的intent对应的广播
ArrayList list = stickies.get(intent.getAction());
if (list != null) {
int N = list.size();
int i;
for (i=0; i> stickies = mStickyBroadcasts.get(userId);
if (stickies == null) {
//因为粘性广播发送过会保存，这里就是保存代码
stickies = new ArrayMap<>();
mStickyBroadcasts.put(userId, stickies);
}
//当前用户的所有粘性广播中查找是否有intent的action相同的广播
ArrayList list = stickies.get(intent.getAction());
if (list == null) {
list = new ArrayList<>();
stickies.put(intent.getAction(), list);
}
final int stickiesCount = list.size();
int i;
for (i = 0; i < stickiesCount; i++) {
if (intent.filterEquals(list.get(i))) {
// This sticky already exists, replace it.
// 新发送的intent在ArrayList中已经有个“相等的”旧intent时，则会用新的替掉旧的
list.set(i, new Intent(intent));
break;
}
}
if (i >= stickiesCount) {
list.add(new Intent(intent));
}
}
我们看到粘性广播的话那么sticky为true，方法首先会检查是否有发送粘性广播的权限。然后会看发送的粘性广播和已经发送的广播是否冲突（当不是发送给所有用户的情况下）。而且我们知道发送过的广播是放在mStickyBroadcasts集合中的，我们发送广播首先要根据用户id查找，然后再从查找的结果中查找与发送intent中action相同的广播。当然粘性广播也是在注册广播的时候添加进来的。接下来我们看看我们的步骤6。
6.动态广播和静态广播注册表的查询
//查找谁会接受这个广播
List receivers = null;//静态注册广播列表
List registeredReceivers = null;//动态注册广播列表
// Need to resolve the intent to interested receivers...
if ((intent.getFlags()&Intent.FLAG_RECEIVER_REGISTERED_ONLY)
== 0) {
//如果只有静态注册广播能接收到广播，那么会查找出来所有匹配的静态注册广播，然后赋值给receivers
receivers = collectReceiverComponents(intent, resolvedType, callingUid, users);
}
if (intent.getComponent() == null) {
if (userId == UserHandle.USER_ALL && callingUid == Process.SHELL_UID) {
// Query one target user at a time, excluding shell-restricted users
for (int i = 0; i < users.length; i++) {
if (mUserController.hasUserRestriction(
UserManager.DISALLOW_DEBUGGING_FEATURES, users[i])) {
continue;
}
//查找所有用户下面的跟这个intent对应的广播接收者，因为接收者可能有多个，
//所以结果放置在List中
List registeredReceiversForUser =
mReceiverResolver.queryIntent(intent,
resolvedType, false, users[i]);
if (registeredReceivers == null) {
registeredReceivers = registeredReceiversForUser;
} else if (registeredReceiversForUser != null) {
registeredReceivers.addAll(registeredReceiversForUser);
}
}
} else {
registeredReceivers = mReceiverResolver.queryIntent(intent,
resolvedType, false, userId);
}
}
我们看到这里会先查找静态注册的广播看有没有，有的话就会赋值给receivers，然后会查找动态注册的广播，有的话会赋值给registeredReceivers，我们接着往下看：
//如果设置了的话，ActivityManagerService就会在当前的系统中查看有没有相同的intent还未被处理，
//如果有的话，就有当前这个新的intent来替换旧的intent。
final boolean replacePending =
(intent.getFlags()&Intent.FLAG_RECEIVER_REPLACE_PENDING) != 0;
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Enqueing broadcast: " + intent.getAction()
+ " replacePending=" + replacePending);
//得到查找到的动态注册的广播数量
int NR = registeredReceivers != null ? registeredReceivers.size() : 0;
if (!ordered && NR > 0) {//如果发送的是无序广播，且查找到的动态注册的广播数量大于0，则分开发送广播
// If we are not serializing this broadcast, then send the
// registered receivers separately so they don't wait for the
// components to be launched.
if (isCallerSystem) {
checkBroadcastFromSystem(intent, callerApp, callerPackage, callingUid,
isProtectedBroadcast, registeredReceivers);
}
//将intent放入广播队列BroadcastQueue 中
final BroadcastQueue queue = broadcastQueueForIntent(intent);
//构建一个广播实体广播实体类
BroadcastRecord r = new BroadcastRecord(queue, intent, callerApp,
callerPackage, callingPid, callingUid, resolvedType, requiredPermissions,
appOp, brOptions, registeredReceivers, resultTo, resultCode, resultData,
resultExtras, ordered, sticky, false, userId);
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Enqueueing parallel broadcast " + r);
final boolean replaced = replacePending && queue.replaceParallelBroadcastLocked(r);
if (!replaced) {
//加入到并行广播队列
queue.enqueueParallelBroadcastLocked(r);
//处理并行队列中的广播
queue.scheduleBroadcastsLocked();
}
registeredReceivers = null;
NR = 0;
}
这个方法就是首先从动态注册广播的集合中查找对应的广播的数量，然后查找到有接收者，那么就将intent封装到BroadcastRecord中，然后放入并行广播队列中，然后调用scheduleBroadcastsLocked()方法进行处理。这里的处理我们等会再说，我们先继续往下看代码：
// Merge into one list.
int ir = 0;
if (receivers != null) {
String skipPackages[] = null;
//防止一些程序发送下面三种广播安装、卸载、更新，这是几个重要的广播，防止有些人加以利用
if (Intent.ACTION_PACKAGE_ADDED.equals(intent.getAction())
|| Intent.ACTION_PACKAGE_RESTARTED.equals(intent.getAction())
|| Intent.ACTION_PACKAGE_DATA_CLEARED.equals(intent.getAction())) {
Uri data = intent.getData();
if (data != null) {
String pkgName = data.getSchemeSpecificPart();
if (pkgName != null) {
skipPackages = new String[] { pkgName };
}
}
} else if (Intent.ACTION_EXTERNAL_APPLICATIONS_AVAILABLE.equals(intent.getAction())) {
skipPackages = intent.getStringArrayExtra(Intent.EXTRA_CHANGED_PACKAGE_LIST);
}
if (skipPackages != null && (skipPackages.length > 0)) {
for (String skipPackage : skipPackages) {
if (skipPackage != null) {
int NT = receivers.size();
for (int it=0; it= curt.priority) {
// Insert this broadcast record into the final list.
receivers.add(it, curr);
ir++;
curr = null;
it++;
NT++;
} else {
// Skip to the next ResolveInfo in the final list.
it++;
curt = null;
}
}
}
//把优先级低于所有静态注册广播接收者的动态广播接收者都追加到receivers列表中的末尾
while (ir < NR) {
if (receivers == null) {
receivers = new ArrayList();
}
receivers.add(registeredReceivers.get(ir));
ir++;
}
我们看到这个方法主要就是做一件事情，就是合并动态注册广播列表和静态注册广播列表，根据优先级来决定排的前后，同样优先级的情况下，动态注册的广播要排在静态注册广播的前面。最后我们看下处理有序广播的过程：
if ((receivers != null && receivers.size() > 0)
|| resultTo != null) {
//根据intent查找到广播队列
BroadcastQueue queue = broadcastQueueForIntent(intent);
//创建广播实体BroadcastRecord
BroadcastRecord r = new BroadcastRecord(queue, intent, callerApp,
callerPackage, callingPid, callingUid, resolvedType,
requiredPermissions, appOp, brOptions, receivers, resultTo, resultCode,
resultData, resultExtras, ordered, sticky, false, userId);
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Enqueueing ordered broadcast " + r
+ ": prev had " + queue.mOrderedBroadcasts.size());
if (DEBUG_BROADCAST) Slog.i(TAG_BROADCAST,
"Enqueueing broadcast " + r.intent.getAction());
boolean replaced = replacePending && queue.replaceOrderedBroadcastLocked(r);
if (!replaced) {
//添加进有序广播队列
queue.enqueueOrderedBroadcastLocked(r);
//处理有序广播队列中的广播
queue.scheduleBroadcastsLocked();
}
} else {
// There was nobody interested in the broadcast, but we still want to record
// that it happened.
if (intent.getComponent() == null && intent.getPackage() == null
&& (intent.getFlags()&Intent.FLAG_RECEIVER_REGISTERED_ONLY) == 0) {
// This was an implicit broadcast... let's record it for posterity.
addBroadcastStatLocked(intent.getAction(), callerPackage, 0, 0, 0);
}
}
这代码跟上面动态注册广播加入到并行广播队列类似，接着就看广播队列中广播的处理过程了，我们知道我们添加到队列中是要拿出来处理的。
7.广播队列中广播的处理
我们从上文知道，我们广播队列的处理是在BroadcastQueue#scheduleBroadcastsLocked()方法进行处理的：
public void scheduleBroadcastsLocked() {
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Schedule broadcasts ["
+ mQueueName + "]: current="
+ mBroadcastsScheduled);
//表示ActivityManagerService当前是不是正在处理其它广播，如果是的话，这里就先不处理直接返回了，保证所有广播串行处理
if (mBroadcastsScheduled) {
return;
}
mHandler.sendMessage(mHandler.obtainMessage(BROADCAST_INTENT_MSG, this));
mBroadcastsScheduled = true;
}
我们看到这个方法主要是发送一个带有BROADCAST_INTENT_MSG标志的消息，这里的mHandler是BroadcastQueue的内部类：
private final class BroadcastHandler extends Handler {
public BroadcastHandler(Looper looper) {
super(looper, null, true);
}
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case BROADCAST_INTENT_MSG: {
if (DEBUG_BROADCAST) Slog.v(
TAG_BROADCAST, "Received BROADCAST_INTENT_MSG");
processNextBroadcast(true);
} break;
case BROADCAST_TIMEOUT_MSG: {
.......
} break;
case SCHEDULE_TEMP_WHITELIST_MSG: {
.......
} break;
}
}
}
我们看到这里的逻辑主要交给了processNextBroadcast()方法处理，这个方法很长，这一篇讲完的话篇幅太长了，那我们留着下一篇继续讲解吧。
总结:我们看到广播的查找过程还是条件很多的，但是总的来说还是比较清晰的，看的过程中希望大家不要急躁，细细地品味。祝大家旅程愉快，最后如果有什么错误或者建议大家可以提出哈。