yandex网站推广,网站建设中企动力公司,苏州工业园区公积金管理中心,论坛程序做导航网站关于mojo binding的官方文档为mojo docs。 由于比较复杂#xff0c;这里只做简单源码分析。
我们知道要实现rpc#xff0c;必须实现客户端和服务端。 mojo 实现了一套领域语言#xff0c;通过领域语言描述接口和数据#xff0c; 再通过特有编译器编译成c代码。 这个过程会…关于mojo binding的官方文档为mojo docs。 由于比较复杂这里只做简单源码分析。
我们知道要实现rpc必须实现客户端和服务端。 mojo 实现了一套领域语言通过领域语言描述接口和数据 再通过特有编译器编译成c代码。 这个过程会生成Mojo对象 我们以content/common/child_process.mojom 为例子来分析。 interface ChildProcess {......// Requests that the process bind a receiving pipe targeting the service// interface named by |receiver|.//// TODO(crbug.com/977637): Rename this to |RunService()| once the above method// is removed.BindServiceInterface(mojo_base.mojom.GenericPendingReceiver receiver);// Requests that the process bind a receiving pipe targeting the interface// named by |receiver|. Unlike |BindServiceInterface()| this may be used to// bind arbitrary interfaces on many different types of child processes.// Calls to this method generally end up in// |ChildThreadImpl::OnBindReceiver()|.//// Whether or not the interface type encapsulated by |receiver| is supported// depends on the process type and potentially on the Content embedder.BindReceiver(mojo_base.mojom.GenericPendingReceiver receiver);......
};我们删除一些接口总体定义如下。生成带c代码如下。 out/Default/gen/content/common/child_process.mojom.h
class CONTENT_EXPORT ChildProcess: public ChildProcessInterfaceBase {public:......// 接口的名字static const char Name_[];// 方法表用于将消息序号转化为处理函数static IPCStableHashFunction MessageToMethodInfo_(mojo::Message message);// 方法名称表static const char* MessageToMethodName_(mojo::Message message);// 协议版本static constexpr uint32_t Version_ 0;static constexpr bool PassesAssociatedKinds_ false;// 是否包含不可中断的方法static constexpr bool HasUninterruptableMethods_ false;using Base_ ChildProcessInterfaceBase;// 代理对象用于客户端调用using Proxy_ ChildProcessProxy;template typename ImplRefTraits// 用于指向服务端实现using Stub_ ChildProcessStubImplRefTraits;// 请求校验器using RequestValidator_ ChildProcessRequestValidator;// 回复校验器using ResponseValidator_ mojo::PassThroughFilter;// 方法版本列表enum MethodMinVersions : uint32_t {kProcessShutdownMinVersion 0,kSetIPCLoggingEnabledMinVersion 0,kGetBackgroundTracingAgentProviderMinVersion 0,kEnableSystemTracingServiceMinVersion 0,kCrashHungProcessMinVersion 0,kRunServiceDeprecatedMinVersion 0,kBindServiceInterfaceMinVersion 0,kBindReceiverMinVersion 0,kSetPseudonymizationSaltMinVersion 0,};......// 下面是方法声明virtual ~ChildProcess() default;......virtual void BindServiceInterface(::mojo::GenericPendingReceiver receiver) 0;virtual void BindReceiver(::mojo::GenericPendingReceiver receiver) 0;......
};
生成的c 类除了方法声明之外还包括如下信息
Name_接口名称MessageToMethodInfo_ 方法表通过收到的消息找到对应的rpc方法。Proxy_ 代理对象通过代理对象调用具体方法组装消息发送给服务端。包括方法名称参数等用于调用服务端对应方法Stub_ 用于描述服务端指向服务端具体实现。RequestValidator_ 请求校验。ResponseValidator_ 响应校验。
通过官方文档我们知道通过Remote 调用服务端方法。 来看一下Remote 是如何实现的。 mojo/public/cpp/bindings/remote.h 887 void ChildProcessProxy::BindServiceInterface(888 ::mojo::GenericPendingReceiver in_receiver) {889 #if BUILDFLAG(MOJO_TRACE_ENABLED)890 TRACE_EVENT1(891 mojom, Send content::mojom::ChildProcess::BindServiceInterface, input_parameters,892 [](perfetto::TracedValue context){893 auto dict std::move(context).WriteDictionary();894 perfetto::WriteIntoTracedValueWithFallback(895 dict.AddItem(receiver), in_receiver,896 value of type ::mojo::GenericPendingReceiver);897 });898 #endif899 const bool kExpectsResponse false;900 const bool kIsSync false;901 const bool kAllowInterrupt true;902 903 const uint32_t kFlags 904 ((kExpectsResponse) ? mojo::Message::kFlagExpectsResponse : 0) |905 ((kIsSync) ? mojo::Message::kFlagIsSync : 0) |906 ((kAllowInterrupt) ? 0 : mojo::Message::kFlagNoInterrupt);907 908 mojo::Message message(909 internal::kChildProcess_BindServiceInterface_Name, kFlags, 0, 0, nullptr);910 mojo::internal::MessageFragment911 ::content::mojom::internal::ChildProcess_BindServiceInterface_Params_Data params(912 message);913 params.Allocate();914 mojo::internal::MessageFragment915 typename decltype(params-receiver)::BaseType receiver_fragment(916 params.message());917 mojo::internal::Serialize::mojo_base::mojom::GenericPendingReceiverDataView(918 in_receiver, receiver_fragment);919 params-receiver.Set(920 receiver_fragment.is_null() ? nullptr : receiver_fragment.data());921 MOJO_INTERNAL_DLOG_SERIALIZATION_WARNING(922 params-receiver.is_null(),923 mojo::internal::VALIDATION_ERROR_UNEXPECTED_NULL_POINTER,924 null receiver in ChildProcess.BindServiceInterface request);925 926 #if defined(ENABLE_IPC_FUZZER)927 message.set_interface_name(ChildProcess::Name_);928 message.set_method_name(BindServiceInterface);929 #endif930 // This return value may be ignored as false implies the Connector has931 // encountered an error, which will be visible through other means.932 ::mojo::internal::SendMojoMessage(*receiver_, message);933 }BindServiceInterface 的主要作用就是组装消息然后发送。 这里908-909行创建Message的时候指定的消息名称为internal::kChildProcess_BindServiceInterface_Name 用于指示服务端调用哪个方法。 这里932行receiver_ 持有一个portal可以将数据写出去。
我们再看服务端怎么处理消息
259 // Implements the mojom ChildProcess interface and lives on the IO thread.
260 class ChildThreadImpl::IOThreadState
261 : public base::RefCountedThreadSafeIOThreadState,
262 public mojom::ChildProcess {......
358
359 void BindServiceInterface(mojo::GenericPendingReceiver receiver) override {
360 if (service_binder_)
361 service_binder_.Run(receiver);
362
363 if (receiver) {
364 main_thread_task_runner_-PostTask(
365 FROM_HERE, base::BindOnce(ChildThreadImpl::BindServiceInterface,
366 weak_main_thread_, std::move(receiver)));
367 }
368 }
369
370 void BindReceiver(mojo::GenericPendingReceiver receiver) override {
371 if (wait_for_interface_binders_) {
372 pending_binding_requests_.push_back(std::move(receiver));
373 return;
374 }
375
376 if (interface_binders_.TryBind(receiver))
377 return;
378
379 main_thread_task_runner_-PostTask(
380 FROM_HERE, base::BindOnce(ChildThreadImpl::OnBindReceiver,
381 weak_main_thread_, std::move(receiver)));
382 }
383 ......457 mojo::Receivermojom::ChildProcess receiver_{this};
458
459 // Binding requests which should be handled by |interface_binders|, but which
460 // have been queued because |allow_interface_binders_| is still |false|.
461 std::vectormojo::GenericPendingReceiver pending_binding_requests_;
462 };
ChildThreadImpl::IOThreadState 实现了mojom::ChildProcess接口。 它持有了一个receiver_对象 该对象持有portal一端 用于处理对端发送的消息。
我们具体来看 mojo::Receivermojom::ChildProcess 的实现。
template typename Interface,typename ImplRefTraits RawPtrImplRefTraitsInterface
class Receiver {
......explicit Receiver(ImplPointerType impl) : internal_state_(std::move(impl)) {}
......private:internal::BindingStateInterface, ImplRefTraits internal_state_;
}Receiver 的参数为ChildThreadImpl::IOThreadState实例。 然后初始化internal_state_变量。internal_state_类型展开宏之后为nternal::BindingStatemojom::ChildProcess, RawPtrImplRefTraitsmojom::ChildProcess internal_state_。
template typename Interface, typename ImplRefTraits
class BindingState : public BindingStateBase {public:using ImplPointerType typename ImplRefTraits::PointerType;explicit BindingState(ImplPointerType impl) {stub_.set_sink(std::move(impl));}......
}这里stub_成员变量为 typename Interface::template Stub_ stub_;展开宏为 mojom::ChildProcess::Stub_ stub_, 也就是ChildProcessStub。 我们看一下它的实现以及set_sink 方法。 out/Default/gen/content/common/child_process.mojom.h template typename ImplRefTraits mojo::RawPtrImplRefTraitsChildProcess
class ChildProcessStub: public mojo::MessageReceiverWithResponderStatus {public:
........void set_sink(ImplPointerType sink) { sink_ std::move(sink); }ImplPointerType sink() { return sink_; }bool Accept(mojo::Message* message) override {if (ImplRefTraits::IsNull(sink_))return false;return ChildProcessStubDispatch::Accept(ImplRefTraits::GetRawPointer(sink_), message);}bool AcceptWithResponder(mojo::Message* message,std::unique_ptrmojo::MessageReceiverWithStatus responder) override {if (ImplRefTraits::IsNull(sink_))return false;return ChildProcessStubDispatch::AcceptWithResponder(ImplRefTraits::GetRawPointer(sink_), message, std::move(responder));}private:ImplPointerType sink_;
};set_sink方法实际设置成员变量sink_ 实际指向ChildThreadImpl::IOThreadState实例。 当receiver收到消息后会调用Accept(异步)方法或者AcceptWithResponder同步返回结果方法。
Accept方法调用ChildProcessStubDispatch::Accept方法第一个参数为sink_, 第二个参数为消息体。我们来看ChildProcessStubDispatch::Accept 方法 out/Default/gen/content/common/child_process.mojom.cc
1021 // static
1022 bool ChildProcessStubDispatch::Accept(
1023 ChildProcess* impl,
1024 mojo::Message* message) {
1025 switch (message-header()-name) {.......
1182 case internal::kChildProcess_BindServiceInterface_Name: {
1183
1184 DCHECK(message-is_serialized());
1185 internal::ChildProcess_BindServiceInterface_Params_Data* params
1186 reinterpret_castinternal::ChildProcess_BindServiceInterface_Params_Data*(
1187 message-mutable_payload());
1188
1189 bool success true;
1190 ::mojo::GenericPendingReceiver p_receiver{};
1191 ChildProcess_BindServiceInterface_ParamsDataView input_data_view(params, message);
1192
1193 if (success !input_data_view.ReadReceiver(p_receiver))
1194 success false;
1195 if (!success) {
1196 ReportValidationErrorForMessage(
1197 message,
1198 mojo::internal::VALIDATION_ERROR_DESERIALIZATION_FAILED,
1199 ChildProcess::Name_, 6, false);
1200 return false;
1201 }
1202 // A null |impl| means no implementation was bound.
1203 DCHECK(impl);
1204 impl-BindServiceInterface(
1205 std::move(p_receiver));
1206 return true;
1207 }
1208 case internal::kChildProcess_BindReceiver_Name: {
1209
1210 DCHECK(message-is_serialized());
1211 internal::ChildProcess_BindReceiver_Params_Data* params
1212 reinterpret_castinternal::ChildProcess_BindReceiver_Params_Data*(
1213 message-mutable_payload());
1214
1215 bool success true;
1216 ::mojo::GenericPendingReceiver p_receiver{};
1217 ChildProcess_BindReceiver_ParamsDataView input_data_view(params, message);
1218
1219 if (success !input_data_view.ReadReceiver(p_receiver))
1220 success false;
1221 if (!success) {
1222 ReportValidationErrorForMessage(
1223 message,
1224 mojo::internal::VALIDATION_ERROR_DESERIALIZATION_FAILED,
1225 ChildProcess::Name_, 7, false);
1226 return false;
1227 }
1228 // A null |impl| means no implementation was bound.
1229 DCHECK(impl);
1230 impl-BindReceiver(
1231 std::move(p_receiver));
1232 return true;
1233 }.......
1259 }
1260 }
1261 return false;
1262 }
函数很简单根据message的名称反序列化参数然后调用ChildThreadImpl::IOThreadState的对应方法。
以上就是典型的ipcz binding 使用。 整体通信借助ipcz 通道。
