Nachos Project 4 Lecturer: Hao-Hua Chu TA: Chun-Po Wang (Artoo) Date: 2008/10/25

2 Project 4 Design and implement appropriate support for multiprogramming Extend the system calls to handle process management and inter- process communication primitives

3 Summary Motivation & Objective Problems Goal 1~7 –1,2,7 10% % % Report –20% Submission

Motivation & Objective Nachos is currently an uni- programming environment Alter Nachos so that each process is maintained in its own system thread 4

Problem Take care of memory allocation and de-allocation Consider all the data and synchronization dependencies between threads. 5

Goal 1 Alter your exceptions to finish the thread instead of halting the system. This will be important, as a run time exception should not cause the operating system to shut down. Modify exception.cc 6

Goal 2 Implement multiprogramming. –The Nachos code is restricted to running one user program at a time. In order to convert the system from uni-programming to multiprogramming. Modify addrspace.h, addrspace.cc, and machine.h 7

Goal 2 You will need to: –A. Come up with a way of allocating physical memory frames so that multiple programs can be loaded into memory at once. –B. Properly handling freeing address space when a user program finishes. 8

Goal 2 –C. It is very important to alter the user program loader algorithm such that it handles frames of information. –Modify NumPhysPages (default 128) variable in machine.h You are not required to deal with limited memory space 9

Goal 3 Create table to store ProcessID (an integer) Implement the ProcessID Exec(char *name) system call. –Exec starts a new user program running within a new system thread. –Figure out how to set up user space inside a system thread. –Path name would be no longer than 256 bytes (including ‘\0’) 10

Goal 3 –Exec should return –1 on failure, else it should return the “ProcessID” of the user level program it just created –More like fork + exec in linux –Execute in /build.linux 11

Goal 4 Implement the int Join(ProcessID id) and void Exit(int exitCode) system calls. –Join will wait and block on a “Process ProcessID ” as noted in its parameter. –Exit returns an exit code to whomever is doing a join. 0 if a program successfully completes, another value if there is an error. 12

Goal 4 –The exit code parameter is set via the exitCode parameter. Join returns the exit code for the process it is blocking on, -1 if the join fails. –A user program can only join to processes that are directly created by the Exec system call. You can not join to other processes or to yourself. 13

Goal 4 –You will have to use semaphores inside your system calls to coordinate Joining and Exiting user processes. 14

Goal 5 Implement the int CreateSemaphore(char *name, int semval) system call. –Modify start.s and syscall.h to add the new system call signatures. –You will create a container at the system level that can hold upto 10 named semaphores. 15

Goal 5 –The CreateSemaphore system call will return 0 on success and –1 on failure. –The CreateSemaphore system call will fail if there are not enough free spots in the container, the name is null, the other semaphore with the same name already exists,or the initial semaphore value is less than 0. 16

Goal 6 Implement int wait(char *name) and int signal(char *name) system calls. –The name parameter is the name of the semaphore. 17

Goal 6 –Both system calls return 0 on success and –1 on failure. –Failure can occur if the user gives an illegal semaphore name (one that has not been created). 18

Goal 7 Sleeping Barber Problem is too difficult (You have to create IPC) So Many Producers to Many Consumers Problem is used to replace. You have to implement two user programs: Producer and Consumer 19

Goal 7 There are 3 kinds of resources: –A, B, C –Use semaphores named “A”, “B”, ”C” respectively Producer produce in a order: A, B, C for 10 times Consumers consume in a order C, B,A for 10 times 20

Goal 7 Producer will print its process ID and resource he creates on screen Consumer will print its process ID and resource he consumes on screen You have to create a system call GetProcessID() to get process ID in user program 21

Goal 7 Use your Print(), PrintNum() to print the output. Use semaphore to avoid interruption during each user program print its output for each line which describes process consumes or produces the resource 22

Goal 7 Output example: –1 produces A –2 produces A –1 produces B –1 produces C –3 consumes C –3 consumes B 23

Goal 7 We will use your CreateSemaphore to create three semaphore with name “A”, “B”, “C” to represent resource A, B, C Then use your Exec to call your two kinds of user program (at most 10 for each) for several time to test your program 24

25 Report Write a 2-page report –Don’t just paste your code, I’ll read it myself –Explain why your implementations would generate correct output –Describe meaningful problems you encountered and how you solved. If your project submission can’t compile and execute on Linux in Workstation Room 217, we will consider it as fail. –Please contact me to apply a workstation account if you need it.

26 Submission Two people in one group (Write down the name and student ID of all members in the report) The file you need to send: 1.A report in.pdf or.doc 2.All the Nachos directory Send your files –Tar your files to an archieve named: os_hw4_bXXXXXXXX_bOOOOOOOO.tar.gz – to with following title: [os_hw4] –Please follow the format carefully or our auto- reply system will not work tar zcvf os_hw4_bXXXXXXXX_bOOOOOOOO.tar.gz report.doc other files...

27 Submission (cont.) Deadline: 12/16 24:00 –For the delayed submission, deduct 5 points for each day DO NOT COPY!! Protect your code well!!