这一次，我们来谈谈广播发送的过程。老规矩先上流程图

1. 常见的通过ContextImpl.java发送广播的方法有以下几种
   => sendBroadcast/sendBroadcastAsUser ：普通广播发送，默认是目前userId，带有“AsUser它是发送给特定的user
   => sendBroadcastMultiplePermissions/sendBroadcastAsUserMultiplePermissions ：有多个权限的广播发送
   => sendOrderedBroadcast/sendOrderedBroadcastAsUser ：发送order有序的广播(order广播是一个接收完成下一个接收，接收者按顺序接收)
   => sendStickyBroadcast/sendStickyBroadcastAsUser ：发送粘性广播，粘性广播是指注册人注册后可立即收到该类型(以前发送的粘性广播)的广播，
   接收人的注册不需要在发送人面前
   => sendStickyOrderedBroadcast/sendStickyOrderedBroadcastAsUser ：发送粘性和顺序order的广播

都是调用AMS的broadcastIntentWithFeature来发送广播

以下是最简单的，只有一个Intent的广播发送

//ContextImpl.java     @Override     public void sendBroadcast(Intent intent) { 
                 warnIfCallingFromSystemProcess();         String resolvedType = intent.resolveTypeIfNeeded(getContentResolver());         try { 
                     intent.prepareToLeaveProcess(this);             //调用AMS的broadcastIntentWithFeature来发送广播             ActivityManager.getService().broadcastIntentWithFeature(                     mMainThread.getApplicationThread(), getAttributionTag(), intent, resolvedType,                     null, Activity.RESULT_OK, nll, null, null, null /*excludedPermissions=*/,
                    AppOpsManager.OP_NONE, null, false, false, getUserId());
        } catch (RemoteException e) { 
        
            throw e.rethrowFromSystemServer();
        }
    }

2. 还是以亮屏SCREEN_ON的广播继续讲解其发送流程
   其调用方法是sendOrderedBroadcastAsUser(ContextImpl.java)->broadcastIntentWithFeature(ActivityManagerService.java)

//Notifier.java
    private final Intent mScreenOnIntent;
	//新建一个Intent，它的action是ACTION_SCREEN_ON，
	//注意此处增加了
	//FLAG_RECEIVER_REGISTERED_ONLY: 只允许动态注册的接收者接受
	//FLAG_RECEIVER_FOREGROUND: 前台接收，也就是前台广播(10s超时)的队列
	//FLAG_RECEIVER_VISIBLE_TO_INSTANT_APPS: 可以被即时app接收
	mScreenOnIntent = new Intent(Intent.ACTION_SCREEN_ON);
	mScreenOnIntent.addFlags(
			Intent.FLAG_RECEIVER_REGISTERED_ONLY | Intent.FLAG_RECEIVER_FOREGROUND
			| Intent.FLAG_RECEIVER_VISIBLE_TO_INSTANT_APPS);

    //亮屏广播发送完成后才调用的
    private final BroadcastReceiver mWakeUpBroadcastDone = new BroadcastReceiver() { 
        
        @Override
        public void onReceive(Context context, Intent intent) { 
        
            //开始发送广播之前会打印类似“power_screen_broadcast_send: 1”的日志
            //这里会在event log中打印类似“power_screen_broadcast_done: [1,125,1]“的日志
			//里面包含了发送亮屏广播的时间，此处是“125 ms”
            EventLog.writeEvent(EventLogTags.POWER_SCREEN_BROADCAST_DONE, 1,
                    SystemClock.uptimeMillis() - mBroadcastStartTime, 1);
            sendNextBroadcast();
        }
    };

   private void sendWakeUpBroadcast() { 
        
        if (DEBUG) { 
        
            Slog.d(TAG, "Sending wake up broadcast.");
        }

        if (mActivityManagerInternal.isSystemReady()) { 
        
            //调用的是ContextImpl的sendOrderedBroadcastAsUser去发送广播
			//mScreenOnIntent是发送的亮屏广播
			//mHandler是PowerManagerService.java的主线程，用来运行mWakeUpBroadcastDone
			//mWakeUpBroadcastDone是亮屏广播发送完成后
            mContext.sendOrderedBroadcastAsUser(mScreenOnIntent, UserHandle.ALL, null,
                    mWakeUpBroadcastDone, mHandler, 0, null, null);
        } else { 
        
            EventLog.writeEvent(EventLogTags.POWER_SCREEN_BROADCAST_STOP, 2, 1);
            sendNextBroadcast();
        }
    }

//ContextImpl.java
    public void sendOrderedBroadcastAsUser(Intent intent, UserHandle user,
            String receiverPermission, BroadcastReceiver resultReceiver, Handler scheduler,
            int initialCode, String initialData, Bundle initialExtras) { 
        
		//多带了appOp=OP_NONE、options=null的参数
        sendOrderedBroadcastAsUser(intent, user, receiverPermission, AppOpsManager.OP_NONE,
                null, resultReceiver, scheduler, initialCode, initialData, initialExtras);
    }

    public void sendOrderedBroadcastAsUser(Intent intent, UserHandle user,
            String receiverPermission, int appOp, Bundle options, BroadcastReceiver resultReceiver,
            Handler scheduler, int initialCode, String initialData, Bundle initialExtras) { 
        
        IIntentReceiver rd = null;
        if (resultReceiver != null) { 
        
            if (mPackageInfo != null) { 
        
                if (scheduler == null) { 
        
                    //由于传入了scheduler(mHandler)，所以这里是不会进来的
                    scheduler = mMainThread.getHandler();
                }
				//进入的是这里获取IIntentReceiver rd(通过mPackageInfo、resultReceiver、scheduler构建)
                rd = mPackageInfo.getReceiverDispatcher(
                    resultReceiver, getOuterContext(), scheduler,
                    mMainThread.getInstrumentation(), false);
            } else { 
        
                if (scheduler == null) { 
        
                    scheduler = mMainThread.getHandler();
                }
                rd = new LoadedApk.ReceiverDispatcher(resultReceiver, getOuterContext(),
                        scheduler, null, false).getIIntentReceiver();
            }
        }
        String resolvedType = intent.resolveTypeIfNeeded(getContentResolver());
        String[] receiverPermissions = receiverPermission == null ? null
                : new String[] { 
        receiverPermission};
        try { 
        
            intent.prepareToLeaveProcess(this);
			//实际是调用的AMS的broadcastIntentWithFeature方法
            ActivityManager.getService().broadcastIntentWithFeature(
                    mMainThread.getApplicationThread(), getAttributionTag(), intent, resolvedType,
                    rd, initialCode, initialData, initialExtras, receiverPermissions,
                    null /*excludedPermissions=*/, appOp, options, true, false,
                    user.getIdentifier());
        } catch (RemoteException e) { 
        
            throw e.rethrowFromSystemServer();
        }
    }

系统AMS通过broadcastIntentWithFeature接收广播的请求

//ActivityManagerService.java
    //从context过来的都走的这个broadcastIntentWithFeature方法，带特性的发送广播
    public final int broadcastIntentWithFeature(IApplicationThread caller, String callingFeatureId,
            Intent intent, String resolvedType, IIntentReceiver resultTo,
            int resultCode, String resultData, Bundle resultExtras,
            String[] requiredPermissions, String[] excludedPermissions, int appOp, Bundle bOptions,
            boolean serialized, boolean sticky, int userId) { 
        
        enforceNotIsolatedCaller("broadcastIntent");
        synchronized(this) { 
        
            intent = verifyBroadcastLocked(intent);

			//通过IApplicationThread获取调用者ProcessRecord callerApp
            final ProcessRecord callerApp = getRecordForAppLOSP(caller);
            final int callingPid = Binder.getCallingPid();
            final int callingUid = Binder.getCallingUid();

            final long origId = Binder.clearCallingIdentity();
            try { 
        
                //获取callerApp、callingPid、callingUid用于广播发送参数传入
                return broadcastIntentLocked(callerApp,
                        callerApp != null ? callerApp.info.packageName : null, callingFeatureId,
                        intent, resolvedType, resultTo, resultCode, resultData, resultExtras,
                        requiredPermissions, excludedPermissions, appOp, bOptions, serialized,
                        sticky, callingPid, callingUid, callingUid, callingPid, userId);
            } finally { 
        
                Binder.restoreCallingIdentity(origId);
            }
        }
    }

    final int broadcastIntentLocked(ProcessRecord callerApp,
            String callerPackage, String callerFeatureId, Intent intent, String resolvedType,
            IIntentReceiver resultTo, int resultCode, String resultData,
            Bundle resultExtras, String[] requiredPermissions, String[] excludedPermissions,
            int appOp, Bundle bOptions, boolean ordered, boolean sticky, int callingPid,
            int callingUid, int realCallingUid, int realCallingPid, int userId) { 
        
        //这里再次增加了3个参数allowBackgroundActivityStarts=false，tokenNeededForBackgroundActivityStarts=false
		//broadcastAllowList=null
        return broadcastIntentLocked(callerApp, callerPackage, callerFeatureId, intent,
                resolvedType, resultTo, resultCode, resultData, resultExtras, requiredPermissions,
                excludedPermissions, appOp, bOptions, ordered, sticky, callingPid, callingUid,
                realCallingUid, realCallingPid, userId, false /* allowBackgroundActivityStarts */,
                null /* tokenNeededForBackgroundActivityStarts */, null /* broadcastAllowList */);
    }

1. 如默认会增加 FLAG_EXCLUDE_STOPPED_PACKAGES ，不让stop(如通过forcestop会设置)的三方app接收静态广播
2. 根据是否粘性广播输出类似的日志：Broadcast (sticky) intent ordered=(true/false) userid=(userId)
3. 解析BroadcastOptions brOptions广播可选参数