【正文】 implemented in one of three ways. 消息隊(duì)列附加在連接上；采用三個(gè)之一的實(shí)現(xiàn)方案 1. Zero capacity – 0 messages 零容量 0 消息 Sender must wait for receiver (rendezvous). 發(fā)送者必須等待接收者 2. Bounded capacity – finite length of n messages 有界容量 n個(gè)消息有限長(zhǎng)度 Sender must wait if link full. 若連接滿了發(fā)送者必須等待 3. Unbounded capacity – infinite length 無界容量 無限長(zhǎng)度 Sender never waits. 發(fā)送者從不等待 Operating System Concepts ClientServer Communication ? Sockets 套接字 ? Remote Procedure Calls 遠(yuǎn)端系統(tǒng)調(diào)用 Operating System Concepts Sockets ? A socket is defined as an endpoint for munication. 套接字定義成通訊中的端 ? Concatenation of IP address and port 與 ip地址和端口相關(guān) ? The socket :1625 refers to port 1625 on host ? Communication consists between a pair of sockets. Operating System Concepts Socket Communication Operating System Concepts Remote Procedure Calls ? Remote procedure call (RPC) abstracts procedure calls between processes on worked systems. RPC是網(wǎng)絡(luò)系統(tǒng)中進(jìn)程之間的系統(tǒng)調(diào)用的抽象 ? Stubs – clientside proxy for the actual procedure on the server. Stub為服務(wù)器端客戶程序的代理 ? The clientside stub locates the server and marshalls the parameters. ? The serverside stub receives this message, unpacks the marshalled parameters, and peforms the procedure on the server. Operating System Concepts Execution of RPC Operating System Concepts Remote Method Invocation ? Remote Method Invocation (RMI) is a Java mechanism similar to RPCs. ? RMI allows a Java program on one machine to invoke a method on a remote object. Operating System Concepts Marshalling Parameters Operating System Concepts Exception Conditions – Error Recovery 異常條件 出錯(cuò)恢復(fù) ? Process terminates 進(jìn)程終止 ? Lost messages 消息丟失 ? Scrambled Messages 消息受損 Operating System Concepts Process: Summary ? An “instantiation” of a program ? System abstraction: the set of resources required for executing a program – Execution context(s) – Address space – File handles, munication endpoints, etc. ? Historically, all of the above “l(fā)umped” into a single abstraction ? More recently, split into several abstractions – Threads, address space, protection domain, etc. ? OS process management: – Supports user creation of processes and interprocess munication (IPC) – Allocates resources to processes according to specific policies – Interleaves the execution of multiple processes to increase system utilization Operating System Concepts Next Time ? Threads ? Read Silberschatz Chapter 5 。發(fā)送者被通知誰是接收者。 } Operating System Concepts Interprocess Communication (IPC) 進(jìn)程間通信 ? Mechanism for processes to municate and to synchronize their actions.用于進(jìn)程通信的機(jī)制，同步其間的活動(dòng) ? Message system – processes municate with each other without resorting to shared variables. 消息系統(tǒng) 進(jìn)程間通信無須對(duì)共享變量進(jìn)行再分類 ? IPC facility provides two operations IPC提供兩個(gè)操作 : – send(message) – message size fixed or variable 發(fā)送 固定或可變大小消息 – receive(message)接受 ? If P and Q wish to municate, they need to 若 P與 Q要通信，需要 : – establish a munication link between them 建立通信連接 – exchange messages via send/receive 通過 send/receive交換消息 ? Implementation of munication link 通信連接的實(shí)現(xiàn) – physical (., shared memory, hardware bus)物理的（如，共享存儲(chǔ)，硬件總線） – logical (., logical properties)邏輯的（如，邏輯特性） Operating System Concepts Implementation Questions 實(shí)現(xiàn)中的問題 ? How are links established? 連接如何建立？ ? Can a link be associated with more than two processes? 連接可同多于兩個(gè)的進(jìn)程相關(guān)嗎？ ? How many links can there be between every pair of municating processes? 每對(duì)在通信進(jìn)程有多少連接？ ? What is the capacity of a link? 一個(gè)連接的容量是多少？ ? Is the size of a message that the link can acmodate fixed or variable? 連接可使用的固定或可變消息的大小？ ? Is a link unidirectional or bidirectional? 連接是無向的還是雙向的？ Operating System Concepts Direct Communication 直接通信