Bài giảng Operating system Concepts - Chapter 4: Processes

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1. Chapter 4: Processes n Process Concept n Process Scheduling n Operations on Processes n Cooperating Processes n Interprocess Communication n Communication in Client-Server Systems Operating System Concepts 4.1 Silberschatz, Galvin and Gagne 2002
2. Process Concept n An operating system executes a variety of programs: F Batch system – jobs F Time-shared systems – user programs or tasks n Textbook uses the terms job and process almost interchangeably. n Process – a program in execution; process execution must progress in sequential fashion. n A process includes: F program counter F stack F data section Operating System Concepts 4.2 Silberschatz, Galvin and Gagne 2002
3. Process State n As a process executes, it changes state F new: The process is being created. F running: Instructions are being executed. F waiting: The process is waiting for some event to occur. F ready: The process is waiting to be assigned to a process. F terminated: The process has finished execution. Operating System Concepts 4.3 Silberschatz, Galvin and Gagne 2002
4. Diagram of Process State Operating System Concepts 4.4 Silberschatz, Galvin and Gagne 2002
5. Process Control Block (PCB) Information associated with each process. n Process state n Program counter n CPU registers n CPU scheduling information n Memory-management information n Accounting information n I/O status information Operating System Concepts 4.5 Silberschatz, Galvin and Gagne 2002
6. Process Control Block (PCB) Operating System Concepts 4.6 Silberschatz, Galvin and Gagne 2002
7. CPU Switch From Process to Process Operating System Concepts 4.7 Silberschatz, Galvin and Gagne 2002
8. Process Scheduling Queues n Job queue – set of all processes in the system. n Ready queue – set of all processes residing in main memory, ready and waiting to execute. n Device queues – set of processes waiting for an I/O device. n Process migration between the various queues. Operating System Concepts 4.8 Silberschatz, Galvin and Gagne 2002
9. Ready Queue And Various I/O Device Queues Operating System Concepts 4.9 Silberschatz, Galvin and Gagne 2002
10. Representation of Process Scheduling Operating System Concepts 4.10 Silberschatz, Galvin and Gagne 2002
11. Schedulers n Long-term scheduler (or job scheduler) – selects which processes should be brought into the ready queue. n Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU. Operating System Concepts 4.11 Silberschatz, Galvin and Gagne 2002
12. Addition of Medium Term Scheduling Operating System Concepts 4.12 Silberschatz, Galvin and Gagne 2002
13. Schedulers (Cont.) n Short-term scheduler is invoked very frequently (milliseconds) (must be fast). n Long-term scheduler is invoked very infrequently (seconds, minutes) (may be slow). n The long-term scheduler controls the degree of multiprogramming. n Processes can be described as either: F I/O-bound process – spends more time doing I/O than computations, many short CPU bursts. F CPU-bound process – spends more time doing computations; few very long CPU bursts. Operating System Concepts 4.13 Silberschatz, Galvin and Gagne 2002
14. Context Switch n When CPU switches to another process, the system must save the state of the old process and load the saved state for the new process. n Context-switch time is overhead; the system does no useful work while switching. n Time dependent on hardware support. Operating System Concepts 4.14 Silberschatz, Galvin and Gagne 2002
15. Process Creation n Parent process create children processes, which, in turn create other processes, forming a tree of processes. n Resource sharing F Parent and children share all resources. F Children share subset of parent’s resources. F Parent and child share no resources. n Execution F Parent and children execute concurrently. F Parent waits until children terminate. Operating System Concepts 4.15 Silberschatz, Galvin and Gagne 2002
16. Process Creation (Cont.) n Address space F Child duplicate of parent. F Child has a program loaded into it. n UNIX examples F fork system call creates new process F exec system call used after a fork to replace the process’ memory space with a new program. Operating System Concepts 4.16 Silberschatz, Galvin and Gagne 2002
17. Processes Tree on a UNIX System Operating System Concepts 4.17 Silberschatz, Galvin and Gagne 2002
18. Process Termination n Process executes last statement and asks the operating system to decide it (exit). F Output data from child to parent (via wait). F Process’ resources are deallocated by operating system. n Parent may terminate execution of children processes (abort). F Child has exceeded allocated resources. F Task assigned to child is no longer required. F Parent is exiting. 4 Operating system does not allow child to continue if its parent terminates. 4 Cascading termination. Operating System Concepts 4.18 Silberschatz, Galvin and Gagne 2002
19. Cooperating Processes n Independent process cannot affect or be affected by the execution of another process. n Cooperating process can affect or be affected by the execution of another process n Advantages of process cooperation F Information sharing F Computation speed-up F Modularity F Convenience Operating System Concepts 4.19 Silberschatz, Galvin and Gagne 2002
20. Producer-Consumer Problem n Paradigm for cooperating processes, producer process produces information that is consumed by a consumer process. F unbounded-buffer places no practical limit on the size of the buffer. F bounded-buffer assumes that there is a fixed buffer size. Operating System Concepts 4.20 Silberschatz, Galvin and Gagne 2002
21. Bounded-Buffer – Shared-Memory Solution n Shared data #define BUFFER_SIZE 10 Typedef struct { . . . } item; item buffer[BUFFER_SIZE]; int in = 0; int out = 0; n Solution is correct, but can only use BUFFER_SIZE-1 elements Operating System Concepts 4.21 Silberschatz, Galvin and Gagne 2002
22. Bounded-Buffer – Producer Process item nextProduced; while (1) { while (((in + 1) % BUFFER_SIZE) == out) ; /* do nothing */ buffer[in] = nextProduced; in = (in + 1) % BUFFER_SIZE; } Operating System Concepts 4.22 Silberschatz, Galvin and Gagne 2002
23. Bounded-Buffer – Consumer Process item nextConsumed; while (1) { while (in == out) ; /* do nothing */ nextConsumed = buffer[out]; out = (out + 1) % BUFFER_SIZE; } Operating System Concepts 4.23 Silberschatz, Galvin and Gagne 2002
24. Interprocess Communication (IPC) n Mechanism for processes to communicate and to synchronize their actions. n Message system – processes communicate with each other without resorting to shared variables. n IPC facility provides two operations: F send(message) – message size fixed or variable F receive(message) n If P and Q wish to communicate, they need to: F establish a communication link between them F exchange messages via send/receive n Implementation of communication link F physical (e.g., shared memory, hardware bus) F logical (e.g., logical properties) Operating System Concepts 4.24 Silberschatz, Galvin and Gagne 2002
25. Implementation Questions n How are links established? n Can a link be associated with more than two processes? n How many links can there be between every pair of communicating processes? n What is the capacity of a link? n Is the size of a message that the link can accommodate fixed or variable? n Is a link unidirectional or bi-directional? Operating System Concepts 4.25 Silberschatz, Galvin and Gagne 2002
26. Direct Communication n Processes must name each other explicitly: F send (P, message) – send a message to process P F receive(Q, message) – receive a message from process Q n Properties of communication link F Links are established automatically. F A link is associated with exactly one pair of communicating processes. F Between each pair there exists exactly one link. F The link may be unidirectional, but is usually bi-directional. Operating System Concepts 4.26 Silberschatz, Galvin and Gagne 2002
27. Indirect Communication n Messages are directed and received from mailboxes (also referred to as ports). F Each mailbox has a unique id. F Processes can communicate only if they share a mailbox. n Properties of communication link F Link established only if processes share a common mailbox F A link may be associated with many processes. F Each pair of processes may share several communication links. F Link may be unidirectional or bi-directional. Operating System Concepts 4.27 Silberschatz, Galvin and Gagne 2002
28. Indirect Communication n Operations F create a new mailbox F send and receive messages through mailbox F destroy a mailbox n Primitives are defined as: send(A, message) – send a message to mailbox A receive(A, message) – receive a message from mailbox A Operating System Concepts 4.28 Silberschatz, Galvin and Gagne 2002
29. Indirect Communication n Mailbox sharing F P1, P2, and P3 share mailbox A. F P1, sends; P2 and P3 receive. F Who gets the message? n Solutions F Allow a link to be associated with at most two processes. F Allow only one process at a time to execute a receive operation. F Allow the system to select arbitrarily the receiver. Sender is notified who the receiver was. Operating System Concepts 4.29 Silberschatz, Galvin and Gagne 2002
30. Synchronization n Message passing may be either blocking or non-blocking. n Blocking is considered synchronous n Non-blocking is considered asynchronous n send and receive primitives may be either blocking or non-blocking. Operating System Concepts 4.30 Silberschatz, Galvin and Gagne 2002
31. Buffering n Queue of messages attached to the link; implemented in one of three ways. 1. Zero capacity – 0 messages Sender must wait for receiver (rendezvous). 2. Bounded capacity – finite length of n messages Sender must wait if link full. 3. Unbounded capacity – infinite length Sender never waits. Operating System Concepts 4.31 Silberschatz, Galvin and Gagne 2002
32. Client-Server Communication n Sockets n Remote Procedure Calls n Remote Method Invocation (Java) Operating System Concepts 4.32 Silberschatz, Galvin and Gagne 2002
33. Sockets n A socket is defined as an endpoint for communication. n Concatenation of IP address and port n The socket 161.25.19.8:1625 refers to port 1625 on host 161.25.19.8 n Communication consists between a pair of sockets. Operating System Concepts 4.33 Silberschatz, Galvin and Gagne 2002
34. Socket Communication Operating System Concepts 4.34 Silberschatz, Galvin and Gagne 2002
35. Remote Procedure Calls n Remote procedure call (RPC) abstracts procedure calls between processes on networked systems. n Stubs – client-side proxy for the actual procedure on the server. n The client-side stub locates the server and marshalls the parameters. n The server-side stub receives this message, unpacks the marshalled parameters, and peforms the procedure on the server. Operating System Concepts 4.35 Silberschatz, Galvin and Gagne 2002
36. Execution of RPC Operating System Concepts 4.36 Silberschatz, Galvin and Gagne 2002
37. Remote Method Invocation n Remote Method Invocation (RMI) is a Java mechanism similar to RPCs. n RMI allows a Java program on one machine to invoke a method on a remote object. Operating System Concepts 4.37 Silberschatz, Galvin and Gagne 2002
38. Marshalling Parameters Operating System Concepts 4.38 Silberschatz, Galvin and Gagne 2002