CS3733: Operating Systems

Transcription

1 Last Lecture Overview CS3733: Operating Systems Topics: Client-Server Model and Connection-Oriented Communication (USP Chapter 18) High-level synchronization structure: Monitor Pthread mutex Conditional variables Barrier Threading Issues Instructor: Dr. Tongping Liu 1 Department of Computer UTSA 2 Quiz Difference between semaphore and mutex lock Binary Semaphore and Mutex Lock? Binary Semaphore: Ø No ownership Mutex lock Ø Only the owner of a lock can release a lock. Ø Priority inversion safety: potentially promote a task Ø Deletion safety: a task owning a lock can t be deleted

2 Client-Server Model Applications with two distinct parts Ø server vs. client Sever: wait for requests from clients Client: makes requests for services from server Examples: Ø Web server vs. clients: http and FireFox, Chrome etc. Ø Mail server vs. clients Ø File server vs. client: nfs 7 8 Client-Server over Internet Client/Server differentiate communication channels using port numbers Communication endpoint Ø Host address: specify which machine Ø Port number: specify which process Ø Standard servers with well-known port numbers ü Mail: 25; http: 80: telnet: 23; ftp: 21 Two approaches for C/S communications Ø Connectionless: server/client embeds info. in every request Ø connection-oriented: setup a connection before sending requests 9 Connection-oriented Client-Server Model Client sets up a connection to server s well-known port number Ø After that, communicate over the private channel Pros and Cons? Pros: Errors can be detected, if no response or overloaded Cons: Initial setup overhead 10 Many Clients vs. One Server Clients use the same passive endpoint initially How does server handle each request? sequentially? Server are typically powerful to handle multiple requests Handle Concurrent Requests Server can fork a child process to handle each request from different clients Ø Too costly, use threads! Ø Apache, nginx: hybrid multi-process multi-threaded. Why?

3 Background: Network Communication Layered network models Ethernet: local area network Inter-network Protocols (IP) Ø Addressing and routing etc. TCP/UDP protocols Ø communication ports and sockets 13 CS5523: Operating UTSA 14 Commonly Used Layer Structure Local Area Network (LAN) Layered structure: layer n uses layer n-1 services Protocols: pairs of software in send/receive nodes Ø Specify the sequence of messages for transmission Ø Specify the format, contents and meanings of data in messages Me ssag e TCP & UDP La yers Application Transport In tern etwo rk Net work inter face Underlyin g ne twor k IP Ethernet In tern etwo rk pa ckets Net work- specif ic packe ts In tern etwo rk pr otocols Underlyin g ne twor k pr otocols CS5523: Operating UTSA 15 not me Shared medium Shared medium: Carrier Sensing Multi-Access. Ø CSMA/CD: collision detection Every Ethernet interface has a unique 48 bit MAC address (a.k.a. hardware address). Ø Example: C0:B3:44:17:21:17 Addresses are assigned to vendors by a central authority (IEEE to manufacturers) CS5523: Operating UTSA 16 What is IP? Network (or Inter-Network) layer protocol Ø packet delivery service (host-to-host). Ø translation between different data-link protocols (Ethernet). IP provides connectionless, unreliable delivery of IP datagram. Ø Connectionless: each datagram is independent. Ø Unreliable (best effort): no guarantee for datagrams to be delivered correctly or at all. IP Packet IP address of source header IP address of destination up to 64 kilobytes VERS HL Service Fragment Length Datagram ID FLAG Fragment Offset TTL Protocol Header Checksum Source Address Destination Address Options (if any) data 1 byte 1 byte 1 byte 1 byte Data CS5523: Operating UTSA 17 CS5523: Operating UTSA 18 3

4 Internet Addresses Internet Addresses (cont.) Logical addresses Ø 32 bits (IPv4, 4 billion, population in early 80s) Includes a network ID and a host ID. Ø Network ID is assigned to an organization by the authority Ø Host IDs are assigned locally by a system administrator Different classes of addresses Ø Class A ü 128 possible network IDs and over 4 million host IDs per network ID Ø Class B ü 16K possible network IDs and 64K host IDs per network ID Ø Class C ü over 2 million possible network IDs and about 256 host IDs per network ID Cl ass D (mu lti cas t): Cl ass E (rese rve d): Cl ass A: 1 to 127 Cl ass B: 128 to 191 Cl ass C: 192 to 223 octet 1 octet 2 octet 3 Netwo rk ID 224 to to 255 Netwo rk ID Netwo rk ID Hos t ID 0 to to to to to to 254 CS5523: Operating UTSA 19 CS5523: Operating UTSA 20 Hos t ID 0 to to to 255 Mu lt i cas t a dd ress Hos t ID 0 to to to to to to 254 Ran ge of ad dre sse to to to to to IP Solves the Routing Problem Programmer's View of TCP/IP Decide the route for each packet Ø necessary in MANs and WANs Update knowledge of the network Ø Adaptive/dynamic routing is usually used: traffic patterns, topological changes Routing decision Ø hop-by-hop, with period update and distribution of traffic data, e.g., the distance-vector, dynamic, distributed algorithm CS5523: Operating UTSA 21 Application TCP IP Application UDP Transport layer: TCP vs. UDP TCP (Transmission Control Protocol): connection-oriented stream service UDP(User Datagram Protocol): connectionless datagram service CS5523: Operating UTSA 22 TCP: Transmission Control Protocol TCP is connection-oriented. Ø 3-way handshake used for connection setup Ø Acknowledge each message (piggyback) (Active) Client Syn Syn + Ack Ack (Passive) Server (Active) Client (Passive) Server Data:N (Data :N+1) Ack Connection Setup 3-way handshake Acknowledgement data packets CS5523: Operating UTSA

5 Socket Abstraction TCP Socket Primitives A socket must be bound to a local port Provide endpoints for communication between processes Socket pair - (local IP address, local port, foreign IP address, foreign port) uniquely identifies a communication channel Primitive Socket Bind Listen Accept Connect Send Recv Close Function Create a new communication endpoint Attach a local address to a socket Announce willingness to accept connections Block caller until a connection request arrives Actively attempt to establish a connection Send some data over the connection Receive some data over the connection Release the connection CS5523: Operating UTSA 25 CS5523: Operating UTSA 26 POSIX Socket System Calls #include <sys/socket.h> int socket(int domain, int type, int protocol); int bind(int s, const struct sockaddr *address, size_t address_len); int listen(int s, int backlog); int accept(int s, struct sockaddr *restrict address, int *restrict address_len); int socket(int domain, int type, int protocol); Ø domain: AF_UNIX or AF_INET Ø type: SOCK_STREAM for connection-oriented TCP or SOCK_DGRAM for connectionless UDP Ø protocol: usually set as 0 POSIX Socket System Calls (cont.) int bind(int s, const struct sockaddr *address, size_t address_len); Ø s: the file descriptor returned by socket Ø address: contains info about the family, port and machine ü For AF_INET it is a struct sockaddr_in which is defined in netinet/in.h ü sa_family_t sin_family; ü in_port_t sin_port; //16 bits port number ü struct in_addr sin_addr; //has to be filled on client side Ø address_len: size of the structure used for the address int listen(int s, int backlog); Ø s: fd of the socket used to accept incoming requests Ø backlog: number of outstanding requests (unaccepted) POSIX Socket System Calls (cont.) int accept(int s, struct sockaddr *restrict address, int *restrict address_len); Ø s: the fd of the socket to accept requests Ø address: information of remote host making request Ø address_len: size of the structure used for the address int connect(int s, struct sockaddr *address, int *address_len); Ø s: the fd of the socket to make requests Ø address: information of remote host accepting request, needs to specify both IP/host_name and port number Ø address_len: size of the structure used for the address POSIX Socket System Calls (cont.) All functions return -1 and set errno Under Linux cc -o server *.c! Under Solaris, need to include socket library cc -o server *.c -lsocket!

6 Client-Server Using TCP Sockets An Example: Server Server side performs first with following actions Ø Step 1: Create socket Ø Step 2: bind server address & port (# known to clients) Ø Step 3: start listen for a connection request Ø Step 4: accept a connection request à create another socket for private communication with the clients Client: create a socket with (IP/host-name, port#), and then try to connect to the server CS5523: Operating UTSA 31 Step 1: Step 2: Step 3: Step 4: int main(int argc, char *argv[]) { int listenfd = 0, connfd = 0; struct sockaddr_in serv_addr; char sendbuff[1025]; time_t ticks; listenfd = socket(af_inet, SOCK_STREAM, 0); memset(&serv_addr, '0', sizeof(serv_addr)); memset(sendbuff, '0', sizeof(sendbuff)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = htonl(inaddr_any); serv_addr.sin_port = htons(5000); bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr)); listen(listenfd, 10); while(1) { connfd = accept(listenfd, (struct sockaddr*)null, NULL); ticks = time(null); snprintf(sendbuff, sizeof(sendbuff), "%.24s\r\n", ctime(&ticks)); write(connfd, sendbuff, strlen(sendbuff)); close(connfd); sleep(1); 32 An Example: Client An Example: Server with Threads Step 1: Step 2: int main(int argc, char *argv[]) { int sockfd = 0, n = 0; char recvbuff[1024]; struct sockaddr_in serv_addr;. //handle input parameters memset(recvbuff, '0',sizeof(recvBuff)); if((sockfd = socket(af_inet, SOCK_STREAM, 0)) < 0){ memset(&serv_addr, '0', sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_port = htons(5000); if(inet_pton(af_inet, argv[1], &serv_addr.sin_addr)<=0) { if( connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0){ while ( (n = read(sockfd, recvbuff, sizeof(recvbuff)-1)) > 0) { recvbuff[n] = 0; if(fputs(recvbuff, stdout) == EOF) { printf("\n Error : Fputs error\n"); return 0; 33 void *connection_handler(void *sd) { time_t ticks; char sendbuff[1025]; int sock = *(int*)sd; ticks = time(null); snprintf(sendbuff, sizeof(sendbuff), "%.24s\r\n", ctime(&ticks)); write( sock, sendbuff, strlen(sendbuff)); close(sock); return 0; int main(int argc, char *argv[]) { int listenfd = 0, connfd = 0; struct sockaddr_in serv_addr; bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr)); listen(listenfd, 10); while(1) { connfd = accept(listenfd, (struct sockaddr*)null, NULL); pthread_create( &ct, NULL, connection_handler, (void*) connfd); 34 Programming with UDP/IP sockets 1. Create the socket 2. Identify the socket (name it) 3. On the server, wait for a message 4. On the client, send a message 5. Send a response back to the client (optional) 6. Close the socket No need to setup the channel

7 UICI: Universal Internet Communication Interface UICI: Client/Server Interaction Abstract the essentials of network communication while hiding the details of programming not part of any UNIX standard