[Mozilla] basic concept analysis of IPDL

Mozilla IPDL

What is? IPDL

• IPDL The full name is “Inter-process-communication Protocol Definiton Language”
• It is an interprocess communication protocol definition language （ More or less like Android Of AIDL)
• It's a way to make C++ The code can be standardized 、 A language that is passed safely between processes or threads
  • Equivalent to a platform independent interface language
  • Mainly aimed at C++ Realization
  • Mozilla private
  • Firfox/FirfoxOS Use IPDL Statement Message(firFoxOS yes KaiOS The forerunner of )
    

IPDL agreement

• Use IPDL Language , Definition IPDL agreement . The agreement states Actors How to communicate between ：
  • Defines the interface for communication
  • Defines the message for communication
    
• Actors:
  • Actors finger IPDL Sender of message ： such as P(Parent)/C(Child) End
  • Parent And Child Corresponding relation ：
    • There is... On the left below Parent、 On the right Child
    • Chrome Process(Browser) <-> Content Process(Render)
    • Content Process(Render) <-> Plugin Process

IPDL And WebIDL

• WebIDL： w3c Standard interface definition language ( Interface Definition Languag), be used for WebAPI Design and development .
• IPDL And WebIDL The relationship between ：
  

IPDL And IPC

• IPC：Inter-Process Communication
• IPDL And IPC The relationship between ：
  • IPDL It can be understood as the protocol layer ： Serialized data 、 Hair / Take the message
  • IPC It can be understood as the transport layer : pipe or socket wait
    

IPDL Main concepts

role (Actor)

• Parent end (Parent) And sub terminal (Child) Called role
• all IPDL The message passes through the parent / Sub send
• Parent-child correspondence ：
  

agreement

• Agreement means by IPDL( Language ) Defined , be used for Actor Specification for communication between
• Protocol type :
  • sync: Synchronous and asynchronous messages can be declared
  • async: Declarable asynchronous messages
  • rpc: It can be stated that RPC news ( Be similar to sync, Try not to use )
• example ：
  • Declared a name of PPlugin Of IPDL agreement
  • Asynchronous messages sent from parent to child : Init()、ShuntDown
  • Asynchronous messages sent from child to parent : Ready()

async protocol PPlugin
{
    
child:
    async Init(nsCString pluginPath);
    async Shutdown();

parent:
    async Ready();
};

Sub protocol (Subprotocols) And protocol management (Protocol Management)

• One IPDL A protocol can have multiple sub protocols , These sub agreements are made by “ The agreement ” management .
  
• Agreement Management
  • The agreement is responsible for the creation of its sub agreements ( All sub agreements , Created through this Agreement )
  • Once the protocol instance is destroyed , Its associated sub agreements will also be destroyed
    

news (Message)

• Message type ：
  • Sync (sync)： Sender blocking , Receive the reply from the receiver directly
  • asynchronous (async)： The sender will not block
  • RPC： Be similar to sync,RPC allow “ Reentrant ” Message handler
    • Sender blocking ,RPC When the answer is called , You can unblock to handle new incoming RPC call
• Return value ：return Keyword representation Message Has a return value
• Sequential delivery ： Pass... In order
• Advice on message types ：
  • Use asynchronous... Whenever possible
  • Synchronization is not recommended
  • Try not to use RPC

Error handling (Error Handling)

• Realization IPDL Message Of C++ Method returns bool type ：
  • ture： success
  • false ： Data corruption or data format error ( Can't recover 、 A disastrous mistake )
• once Message The implementation of returns False, It will be dealt with as follows ：
  • The communication channels for the child process disconnected
  • Terminate Process
• Suggestions for error handling ： about “ Normal error ”、“ Non lethal ” Error of , There is no need to return False

ShutDown( close )

• When the management agreement is destroyed , All sub agreements need to be notified ：
  • No more messages
  • Through the management agreement , Destroy all its associated sub agreements

IPDL Exmaple

• Exmaple structure :JS call WebAPI,JS Engine call WebAPI Impl,WebAPI adopt IPLD Conduct IPC signal communication .
  
• The implementation of this part , please Mozilla Official website ：
  https://developer.mozilla.org/en-US/docs/Mozilla/IPDL/Extending_a_Protocol

Reference material

• IPDL Tutorial
• Extending a Protocol
• IPDL Type Serialization
• IPDL Best Practices
• Glossary
• PBackground
• IPDL-Mozilla Wiki