CS 213, Fall 2000Homework Assignment H4: Writing concurrent programsAssigned: Nov. 16, Due: Wed., Nov. 29, 11:59PMNovember 15, 2000Dave O’Hallaron ([email protected]) is the lead person for this lab.The purpose of this assignment is to help you become more familiar with different styles of concurrentprogramming and exceptional control flow.LogisticsYou must work alone on this assignment. All the files you need are in the directory:/afs/cs.cmu.edu/academic/class/15213-f00/H4Start by copying the file H4.tar from that directory to a (protected) directory in which you plan to doyour work. Then give the command: tar xvf H4.tar. This will cause 8 files to be unpacked into thedirectory: 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 tfgets-thread.c files. Enter your Andrew login ID at the top of each these two files. Do this right away soyou don’t forget.DescriptionThe standard library functionchar *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 returnss. If we were to call fgets with the stdin stream,char *s = fgets(s, BUFSIZE, stdin);1then 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 within5 seconds, then tfgets behaves just like fgets, immediately returning a pointer to s. If 5 seconds elapsewithout 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 otherbased on threads:tfgets-proc.c: This solution will implement tfgets using processes, signals, and nonlocaljumps.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 (tfgets-main.c) that calls tfgets and prints the result. The output is a pair of binaries called tfgets-procand tfgets-thread. If your solutions are working properly, these binaries will immediately echo theinput 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.RulesDo 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.EvaluationEach solution is worth 5 points, for a total of 10 points.Hints and suggestionsTo 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 followingLinux 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, whichkills a peer thread.2Programming with processes, signals, and non-local jumps is described in detail in Handout 6: Ex-ceptional Control Flow.Because your process-based solution will need to perform a nonlocal jump from a signal handler, youmust 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, theirbehaviors and interfaces are identical.The pause function, which we haven’t discussed in class, simply blocks the process and waits for asignal to arrive.We have included some error-handling wrapper routines in ics.c that might be helpful to you. Youare not required to use them.Remember that man pages are your friends. For example, type man pthread cancel to learnmore about the pthread cancel function.Hand inTo handin your tfgets-proc.c and tfgets-thread.c files, typemake handin NAME=usernamewhere username is your Andrew login ID. After the handin, if you discover a mistake and want to submita revised copy, typemake handin NAME=username VERSION=2You can verify your handin by looking in/afs/cs.cmu.edu/academic/class/15213-f00/H4/handinYou have list and insert permissions in this directory, but no read or write
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