CS 213 Fall 2000 Homework Assignment H4 Writing concurrent programs Assigned Nov 16 Due Wed Nov 29 11 59PM November 15 2000 Dave O Hallaron droh cs cmu edu is the lead person for this lab The purpose of this assignment is to help you become more familiar with different styles of concurrent programming and exceptional control flow Logistics You must work alone on this assignment All the files you need are in the directory afs cs cmu edu academic class 15213 f00 H4 Start by copying the file H4 tar from that directory to a protected directory in which you plan to do your work Then give the command tar xvf H4 tar This will cause 8 files to be unpacked into the directory README Makefile ics c ics h tfgets main c tfgets h tfgets proc c tfgets thread c You will be modifying and handing in the tfgets proc c and tfgetsthread c files Enter your Andrew login ID at the top of each these two files Do this right away so you don t forget Description The standard library function char fgets char s int size FILE stream reads in at most size 1 characters from stream stores them into the buffer pointed to by s and returns s If we were to call fgets with the stdin stream char s fgets s BUFSIZE stdin 1 then fgets would block possibly forever until we typed something and hit the return key Your task is to develop a timeout version of fgets called tfgets If the user types an input string within 5 seconds then tfgets behaves just like fgets immediately returning a pointer to s If 5 seconds elapse without any keyboard input then tfgets times out and returns NULL to the caller You will develop two different solutions in two different source files one based on processes and the other based on threads tfgets proc c This solution will implement tfgets using processes signals and nonlocal jumps tfgets thread c This solution will implement tfgets using threads Type make to compile your solutions and link each of them with a simple driver routine tfgetsmain c that calls tfgets and prints the result The output is a pair of binaries called tfgets proc and tfgets thread If your solutions are working properly these binaries will immediately echo the input string if you type something within 5 seconds Otherwise they will timeout by printing BOOM We will evaluate the correctness of your solutions using the tfgets main c driver Rules Do all your work on the fish machines Do not use the alarm function in any of your solutions Reap all child processes and peer threads before returning to the caller Do not mix signals and threads Evaluation Each solution is worth 5 points for a total of 10 points Hints and suggestions To help you get started we have included templates for tfgets proc c and tfgets thread c You may modify these files any way you wish Expect your solution to be about 60 80 lines of C code Our process based solution uses the following Linux functions fork wait signal sleep kill sigsetjmp siglongjmp and pause Our threads based solution uses pthread cond signal and pthread cond timedwait along with the usual calls for creating and reaping threads We also use pthread cancel which kills a peer thread 2 Programming with processes signals and non local jumps is described in detail in Handout 6 Exceptional Control Flow Because your process based solution will need to perform a nonlocal jump from a signal handler you must use sigsetjmp and siglongjmp rather than their setjmp and longjmp counterparts Other than the fact that the former can be used from signal handlers while the latter cannot their behaviors and interfaces are identical The pause function which we haven t discussed in class simply blocks the process and waits for a signal to arrive We have included some error handling wrapper routines in ics c that might be helpful to you You are not required to use them Remember that man pages are your friends For example type man pthread cancel to learn more about the pthread cancel function Hand in To handin your tfgets proc c and tfgets thread c files type make handin NAME username where username is your Andrew login ID After the handin if you discover a mistake and want to submit a revised copy type make handin NAME username VERSION 2 You can verify your handin by looking in afs cs cmu edu academic class 15213 f00 H4 handin You have list and insert permissions in this directory but no read or write permissions 3
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