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Transcript
Communication
Asynchronous RPC (1)
2-12
a)
b)
The interconnection between client and server in a
traditional RPC
The interaction using asynchronous RPC
Asynchronous RPC (2)
2-13
A client and server interacting through two asynchronous RPCs
Message-Oriented Communication
• RPCs and RMIs are not always appropriate
– Both assume that receiver is executing when a request
is issued
– Inherently synchronous
• Buffer-based network model
– Hosts are connected to communication servers
– Message buffers at end hosts and communication
servers
– Example: Email system
Message Oriented Transient
Communication -Berkeley Sockets
• Interface for transport layer
• A communications end point
Primitive
Meaning
Socket
Create a new communication endpoint
Bind
Attach a local address to a socket
Listen
Announce willingness to accept connections
Accept
Block caller until a connection request arrives
Connect
Actively attempt to establish a connection
Send
Send some data over the connection
Receive
Receive some data over the connection
Close
Release the connection
Socket primitives for TCP/IP.
Berkeley Sockets
Connection-oriented communication pattern using sockets.
Message-Passing Interface
• Multi-computers need low-overhead communication
primitives
• Sockets are not suitable
• Send/Receive primitives are too simple
• Not optimized for proprietary protocols
• Provides transient asynchronous communication
• Local and remote buffers
• Identification by (groupID, processID)
MPI Primitives
Message Oriented Persistent Comm.
• Message Queuing Systems or Message-Oriented
Middleware (MoM)
• Incorporates support for persistent asynchronous
communication
• Offers intermediate-term storage capacity
– Neither sender or receiver need to be active for the entire
communication duration
Message Queuing Model
• Applications communicate through messages stored
in queues
• Each application has its own (local) queue
• Guarantees that the message will be inserted in
recipient’s queue
– No guarantee about time or whether receiver reads the
message
• Supports loosely coupled communication
Message-Queuing Model (1)
2-26
Four combinations for loosely-coupled communications using queues.
Message-Queuing Model (2)
Primitive
Meaning
Put
Append a message to a specified queue
Get
Block until the specified queue is nonempty, and remove the first message
Poll
Check a specified queue for messages, and remove the first. Never block.
Notify
Install a handler to be called when a message is put into the specified
queue.
Basic interface to a queue in a message-queuing system.
General Architecture of a Message-Queuing System (1)
•
•
•
•
Source Queue/Destination Queue
Each queue has a unique name
Queuing system maps queue names to network address
Queue managers and relays
General Architecture of a Message-Queuing System (2)
2-29
The general organization of a message-queuing system with routers.
Message Brokers
• Message brokers convert messages to a format required by
destination application
2-30