Android广播Broadcast的启动流程是什么寻技术

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广播的注册

我们常在

Activity

或

Service

、甚至

Application

中调用

registerReceiver

函数来注册动态广播，该函数其实来自它们共同的父类

ContextWrapper

中。

ContextWrapper

是

Context

的子类，我们会在介绍

Context

的文章介绍它们的关系。

public Intent registerReceiver(
    BroadcastReceiver receiver, IntentFilter filter) {
    return mBase.registerReceiver(receiver, filter);
}

这里

Context

类型的

mBase

，在

Activity

的创建过程实际被赋值为

ContextImpl

实例。

public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter) {
    return registerReceiver(receiver, filter, null, null);
}
public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter,
    String broadcastPermission, Handler scheduler) {
	return registerReceiverInternal(receiver, getUserId(),
        	filter, broadcastPermission, scheduler, getOuterContext(), 0);
}

经过

registerReceiver

重载函数，调用了

registerReceiverInternal

函数。

    private Intent registerReceiverInternal(BroadcastReceiver receiver, int userId,
            IntentFilter filter, String broadcastPermission,
            Handler scheduler, Context context, int flags) {
        IIntentReceiver rd = null;
        //分析一
        if (receiver != null) {
            if (mPackageInfo != null &amp;&amp; context != null) {
                if (scheduler == null) {
                    scheduler = mMainThread.getHandler();
                }
                rd = mPackageInfo.getReceiverDispatcher(
                    receiver, context, scheduler,
                    mMainThread.getInstrumentation(), true);
            } else {
                if (scheduler == null) {
                    scheduler = mMainThread.getHandler();
                }
                rd = new LoadedApk.ReceiverDispatcher(
                        receiver, context, scheduler, null, true).getIIntentReceiver();
            }
        }
        try {
        	分析二：
            final Intent intent = ActivityManager.getService().registerReceiverWithFeature(
                    mMainThread.getApplicationThread(), mBasePackageName, getAttributionTag(), rd,
                    filter, broadcastPermission, userId, flags);
            if (intent != null) {
                intent.setExtrasClassLoader(getClassLoader());
                intent.prepareToEnterProcess();
            }
            return intent;
        } catch (RemoteException e) {
            throw e.rethrowFromSystemServer();
        }
    }

分析一:

传递进来的

BroadcastReceiver

不为

null

，

LoadedApk

类型的

mPackageInfo

只要应用进程启动，该属性就会被赋值，

context

这里指向

Activity

。

scheduler

为

null

，赋值为主线程的

类型

mH

对象。分析一，主要通过上面的变量来获得

IIntentReceiver

类型

rd

对象。

getReceiverDispatcher

函数先从缓存检测是否有相同类型的

BroadcastReceiver

对应的

ReceiverDispatcher

。没有的话，则新建并缓存起来。一个

context

对应多个

BroadcastReceiver

，而一个

BroadcastReceiver

对应用一个

ReceiverDispatcher

。

ReceiverDispatcher

是

LoadedDispatcher

的静态内部类，其内部还有一个

AIDL

类型本地实现静态类

InnerReceiver

。在

ReceiverDispatcher

的构造函数中会创建

InnerReceiver

的实例。

public IIntentReceiver getReceiverDispatcher(BroadcastReceiver r,
        Context context, Handler handler,
        Instrumentation instrumentation, boolean registered) {
    synchronized (mReceivers) {
        LoadedApk.ReceiverDispatcher rd = null;
        ArrayMap<BroadcastReceiver, LoadedApk.ReceiverDispatcher> map = null;
        if (registered) {
            map = mReceivers.get(context);
            if (map != null) {
                rd = map.get(r);
            }
        }
        if (rd == null) {
            rd = new ReceiverDispatcher(r, context, handler,
                    instrumentation, registered);
            if (registered) {
                if (map == null) {
                    map = new ArrayMap<BroadcastReceiver, LoadedApk.ReceiverDispatcher>();
                    mReceivers.put(context, map);
                }
                map.put(r, rd);
            }
        } else {
            rd.validate(context, handler);
        }
        rd.mForgotten = false;
        return rd.getIIntentReceiver();
    }
}

回到

registerReceiverInternal

函数的分析二，调用了

AMS

的

registerReceiverWithFeature

函数。

该函数是

Broadcast

整个注册过程结束的地方，根据新注册的

BroadcastReceiver

，处理粘性广播的发送和当前注册

Receiver

的添加。

分析一：

粘性广播存储在AMS的

SparseArray<ArrayMap<String, ArrayList<Intent>>>

类型的

mStickyBroadcasts

中。

SparseArray

的

key

为

userId

,而

ArrayMap

的

key

为

action

value

为

Intent

。即我们可以通过用户id在

mStickyBroadcasts

找到当前进程对应所有粘性广播（和针对所有进程的粘性广播），然后根据对应的

action

找到对应的

Intent

。这里将他们收集到

stickyIntents

集合中。

分析二：

所有广播的接收者

BroacastReceiver

存储在

AMS

类

HashMap<IBinder, ReceiverList>

类型的

mRegisteredReceivers

中。这里的

IBinder

类型就是应用进程前面创建的

InnerReceiver

类实例在AMS的引用。因为广播接收者

BroadcastReceiver

对应一个或多个

Broadcast

,所以这里通过继承自

ArrayList<BroadcastFilter>

的

ReceiverList

来表达这种关系。通过

BroadcastFilter

来表示当前接收者感兴趣的广播。

分析三：

对匹配到的粘性Intent进入广播队列广播。

    public Intent registerReceiverWithFeature(IApplicationThread caller, String callerPackage,
            String callerFeatureId, IIntentReceiver receiver, IntentFilter filter,
            String permission, int userId, int flags) {
        enforceNotIsolatedCaller("registerReceiver");
		//粘性Intent
		ArrayList<Intent> stickyIntents = null;
        ProcessRecord callerApp = null;
        final boolean visibleToInstantApps
                = (flags & Context.RECEIVER_VISIBLE_TO_INSTANT_APPS) != 0;
        int callingUid;
        int callingPid;
        boolean instantApp;
        synchronized(this) {
            if (caller != null) {
            	//获得当前引用进程的ProcessRecord
                callerApp = getRecordForAppLocked(caller);
               	...
                callingUid = callerApp.info.uid;
                callingPid = callerApp.pid;
            } else {
                callerPackage = null;
                callingUid = Binder.getCallingUid();
                callingPid = Binder.getCallingPid();
            }
			//是否快应用（类似小程序）
            instantApp = isInstantApp(callerApp, callerPackage, callingUid);
            userId = mUserController.handleIncomingUser(callingPid, callingUid, userId, true,
                    ALLOW_FULL_ONLY, "registerReceiver", callerPackage);
			//分析一：当前注册广播中感兴趣的action列表
            Iterator<String> actions = filter.actionsIterator();
            if (actions == null) {
                ArrayList<String> noAction = new ArrayList<String>(1);
                noAction.add(null);
                actions = noAction.iterator();
            }
			//从历史粘性广播中查找与当前注册的action一致的intent
			//添加到stickyIntents
            // Collect stickies of users
            int[] userIds = { UserHandle.USER_ALL, UserHandle.getUserId(callingUid) };
            while (actions.hasNext()) {
                String action = actions.next();
                for (int id : userIds) {
                    ArrayMap<String, ArrayList<Intent>> stickies = mStickyBroadcasts.get(id);
                    if (stickies != null) {
                        ArrayList<Intent> intents = stickies.get(action);
                        if (intents != null) {
                            if (stickyIntents == null) {
                                stickyIntents = new ArrayList<Intent>();
                            }
                            stickyIntents.addAll(intents);
                        }
                    }
                }
            }
        }
		//处理content类型的Intent
        ArrayList<Intent> allSticky = null;
        if (stickyIntents != null) {
            final ContentResolver resolver = mContext.getContentResolver();
            // Look for any matching sticky broadcasts...
            for (int i = 0, N = stickyIntents.size(); i < N; i++) {
                Intent intent = stickyIntents.get(i);
                // Don't provided intents that aren't available to instant apps.
                if (instantApp &&
                        (intent.getFlags() & Intent.FLAG_RECEIVER_VISIBLE_TO_INSTANT_APPS) == 0) {
                    continue;
                }
                //当前注册广播IntentFilter是否与action一致的intent的匹配
                //处理content类型
                if (filter.match(resolver, intent, true, TAG) >= 0) {
                    if (allSticky == null) {
                        allSticky = new ArrayList<Intent>();
                    }
                    allSticky.add(intent);
                }
            }
        }
        //receiver为null，直接返回null或者第一个粘性intent
        Intent sticky = allSticky != null ? allSticky.get(0) : null;
        if (receiver == null) {
            return sticky;
        }
        synchronized (this) {
            ...
            //分析二：
			//从缓存或新建ReceiverList对象，与Receiver绑定
            ReceiverList rl = mRegisteredReceivers.get(receiver.asBinder());
            if (rl == null) {
                rl = new ReceiverList(this, callerApp, callingPid, callingUid,
                        userId, receiver);
                if (rl.app != null) {
                    final int totalReceiversForApp = rl.app.receivers.size();
                    if (totalReceiversForApp >= MAX_RECEIVERS_ALLOWED_PER_APP) {
                        throw new IllegalStateException("Too many receivers, total of "
                                + totalReceiversForApp + ", registered for pid: "
                                + rl.pid + ", callerPackage: " + callerPackage);
                    }
					//添加到ProcessRecord记录中
                    rl.app.receivers.add(rl);
                } else {
                    try {
                        receiver.asBinder().linkToDeath(rl, 0);
                    } catch (RemoteException e) {
                        return sticky;
                    }
                    rl.linkedToDeath = true;
                }
                mRegisteredReceivers.put(receiver.asBinder(), rl);
            }
            ...
			//新建BroadcastFilter，并添加到BroadcastList
            BroadcastFilter bf = new BroadcastFilter(filter, rl, callerPackage, callerFeatureId,
                    permission, callingUid, userId, instantApp, visibleToInstantApps);
            if (rl.containsFilter(filter)) {
                ...
            } else {
                rl.add(bf);
                //添加到接收者解析器
                mReceiverResolver.addFilter(bf);
            }
            // Enqueue broadcasts for all existing stickies that match
            // this filter.
            //分析三：对匹配到action的粘性广播进行广播
            if (allSticky != null) {
                ArrayList receivers = new ArrayList();
                receivers.add(bf);
                final int stickyCount = allSticky.size();
                for (int i = 0; i < stickyCount; i++) {
                    Intent intent = allSticky.get(i);
                    BroadcastQueue queue = broadcastQueueForIntent(intent);
                    BroadcastRecord r = new BroadcastRecord(queue, intent, null,
                            null, null, -1, -1, false, null, null, OP_NONE, null, receivers,
                            null, 0, null, null, false, true, true, -1, false,
                            false /* only PRE_BOOT_COMPLETED should be exempt, no stickies */);
                    queue.enqueueParallelBroadcastLocked(r);
                    queue.scheduleBroadcastsLocked();
                }
            }
            return sticky;
        }
    }

广播的解注册

回到

ContextWrapper

的

unregisterReceiver

函数。

#ContextWrapper
public void unregisterReceiver(BroadcastReceiver receiver) {
    mBase.unregisterReceiver(receiver);
}
#ContextImpl
public void unregisterReceiver(BroadcastReceiver receiver) {
    if (mPackageInfo != null) {
        IIntentReceiver rd = mPackageInfo.forgetReceiverDispatcher(
                getOuterContext(), receiver);
        try {
            ActivityManager.getService().unregisterReceiver(rd);
        } catch (RemoteException e) {
            throw e.rethrowFromSystemServer();
        }
    } else {
        throw new RuntimeException("Not supported in system context");
    }
}

这里通过

receiver

和

context

获得

IIntentReceiver

实例

rd

，然后调用AMS的

unregisterReceiver

函数。其中

LoadedApk

的

forgetReceiverDispatcher

函数，主要是从

mReceivers

获取

IIntentReceiver

的实例，并将

receiver

对应的内容从缓存移除。

AMS的

unregisterReceiver

函数。主要是将注册过程添加到

mRegisteredReceivers

、

ProcessProcess

.Receivers、

mReceiverResolver

中对应的内容移除。并终止正在发送的广播。

   public void unregisterReceiver(IIntentReceiver receiver) {
		...
        final long origId = Binder.clearCallingIdentity();
        try {
            boolean doTrim = false;
            synchronized(this) {
            	//获得当前对应的ReceiverList
                ReceiverList rl = mRegisteredReceivers.get(receiver.asBinder());
                if (rl != null) {
					//默认情况为null，看看广播发送是否会赋值
					//从处理逻辑来看，就是广播内容
                    final BroadcastRecord r = rl.curBroadcast;
                    if (r != null &amp;&amp; r == r.queue.getMatchingOrderedReceiver(r)) {
                        final boolean doNext = r.queue.finishReceiverLocked(
                                r, r.resultCode, r.resultData, r.resultExtras,
                                r.resultAbort, false);
                        if (doNext) {
                            doTrim = true;
                            r.queue.processNextBroadcast(false);
                        }
                    }
					//从processRecord中移除
                    if (rl.app != null) {
                        rl.app.receivers.remove(rl);
                    }
                    //从mRegisteredReceivers和mReceiverResolver移除
                    removeReceiverLocked(rl);
                    if (rl.linkedToDeath) {
                        rl.linkedToDeath = false;
                        rl.receiver.asBinder().unlinkToDeath(rl, 0);
                    }
                }
            }
            // If we actually concluded any broadcasts, we might now be able
            // to trim the recipients' apps from our working set
            if (doTrim) {
                trimApplications(OomAdjuster.OOM_ADJ_REASON_FINISH_RECEIVER);
                return;
            }
        } finally {
            Binder.restoreCallingIdentity(origId);
        }
    }
void removeReceiverLocked(ReceiverList rl) {
    mRegisteredReceivers.remove(rl.receiver.asBinder());
    for (int i = rl.size() - 1; i &gt;= 0; i--) {
        mReceiverResolver.removeFilter(rl.get(i));
    }
}

广播的发送

定位到

ContextWrapper

的

sendBroadcast

函数。

public void sendBroadcast(Intent intent) {
    mBase.sendBroadcast(intent);
}
public void sendBroadcast(Intent intent) {
    warnIfCallingFromSystemProcess();
    String resolvedType = intent.resolveTypeIfNeeded(getContentResolver());
    try {
        intent.prepareToLeaveProcess(this);
        ActivityManager.getService().broadcastIntentWithFeature(mMainThread.getApplicationThread(), getAttributionTag(), intent, resolvedType,null, Activity.RESULT_OK, null, null, null, AppOpsManager.OP_NONE, nul

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Tags：流程 Android 启动

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