Description
Learning GOALS The purpose of this assignment is to gain insight into the asynchronous nature of interrupts and signals. You’ll be writing three programs to explore these concepts, which will expand your C programming skills. A Periodic ALARM For this alarm part, you’ll be writing two programs called mySigHandler.c and sendsig.c. The first program will handle three signals: a periodic signal from an alarm, a keyboard interrupt signal, and a user defined signal. The second program will be used to send signals to other programs including mySigHandler.c. Reminder: You are to do this work on the CS instructional lab machines. The setup and handling of signals is different on different platforms and might not work the same on other machines as it does in the CS lab machines. Setting up the Alarm Write a program, mySigHandler.c, with just a main() function that runs an infinite loop such as: while (1){ } 2020/12/19 p6: Signal Handling https://canvas.wisc.edu/courses/205087/assignments/934459 2/10 Before entering the infinite loop, the main() function has to do two things. First, it sets up an alarm that will go off 3 seconds later, causing a SIGALRM signal to be sent to the program. Second, it registers a signal handler to handle the SIGALRM signal so that signal can be received by the program. The signal handler is just another function you need to write inside your program. This handler function should print the pid (process id) of the program and the current time (in the same format as the Linux date command). It should also re-arm the alarm to go off again three seconds later, and then return back to the main function, which continues its infinite loop. At this stage, the output will look like this: [deppeler@liederkranz] (44)$ ls mySigHandler* mySigHandler.c [deppeler@liederkranz] (45)$ ./mySigHandler Pid and time print every 3 seconds. Enter Ctrl-C to end the program. PID: 6280 CURRENT TIME: Tue Nov 24 21:44:01 2020 PID: 6280 CURRENT TIME: Tue Nov 24 21:44:04 2020 PID: 6280 CURRENT TIME: Tue Nov 24 21:44:07 2020 PID: 6280 CURRENT TIME: Tue Nov 24 21:44:10 2020 PID: 6280 CURRENT TIME: Tue Nov 24 21:44:13 2020 ^C [deppeler@liederkranz] (46)$ Notice that to stop the program from running, you type in a Ctrl+c (^C in the output above) in the command shell where the program is running. Typing Ctrl+c sends an interrupt signal (called SIGINT) to the running program. The default behavior of the SIGINT signal is to terminate the program. Since both main() and the alarm handler need to know/use the number of seconds in order to arm the alarm, make this value a global variable. Recall that signal handlers are not called directly in the program. They cannot receive arguments from other functions in the program and so we’ll use global variables to share information with them. You’ll use library functions and system calls to write the above program. It is important to check the return values of these functions, so that your program detects error conditions and acts in response to those errors. Refer the man pages of the following functions that you will use. To use the man pages, just type man at the Linux prompt. The manual section numbers will be either 2 (system calls) or 3 (C library functions). Read more on how to use man pages http://www.linfo.org/man.html (http://www.linfo.org/man.html) time() and ctime(): are library calls to help your handler function obtain and print the time in the correct format. getpid(): is a system call to help your handler function obtain the pid of the program. alarm(): is used to set a SIGALRM signal to occur in a specified number of seconds. sigaction(): is used to register a handler function to be called when the specific type of signal (specified as the first parameter) is sent to the program. You will need to create multiple handlers 2020/12/19 p6: Signal Handling https://canvas.wisc.edu/courses/205087/assignments/934459 3/10 where each is connected to its particular function. You are particularly interested in setting the sa_handler field of the structure that sigaction() needs; it specifies the handler function to run upon receiving the signal. DO NOT USE the signal() system call; instead, use sigaction() to register your handler. Note: Make sure to initialize the sigaction struct via memset() so that it is cleared (i.e, zeroed out) before you use it. struct sigaction act; memset (&act, 0, sizeof(act)); User Defined Signals Linux has two basic user defined signals, SIGUSR1 and SIGUSR2. As the name suggests these signals are defined by a user program, which is free to choose whatever action it should take on catching these signals. Extend your implementation of mySigHandler.c so that it prints a message on receiving a SIGUSR1 signal. It should also increment a global counter to keep tally of the number of times it receives SIGUSR1. To achieve this, you will need to write another signal handler and register it to handle the SIGUSR1 signal using sigaction() one more time. Test your implementation by using the kill command at the Linux prompt to send a SIGUSR1 signal to mySigHandler.c. Later in this assignment, you will implement a small program that can be used to send signals to other programs. See the user manual command man kill to see how to use the kill command to send user signals and interrupts from the Linux prompt. Note: If you are working remotely in different remote sessions, make sure that the different ssh sessions are on the same Linux machine (e.g., rockhopper-04). Otherwise sending signals from a program in one session to a program (pid) in another session is going to fail. Handling the Ctrl-C the Keyboard Interrupt Signal The last modification you’ll make to your mySigHandler.c program will change the default behavior that occurs when Ctrl+c (read as “control C”) is typed. Ctrl-C is the keyboard interrupt signal. When Ctrl-C is signaled, the mySigHandler program should first print the number of times it received the SIGUSR1 signal (from the sendsig program explained later) and then call exit(0). To handle the keyboard interrupt signal, you will need to write another signal handler and register it to handle the SIGINT signal again using sigaction(). With this modification the output of the program should look something like this: [deppeler@liederkranz] (66)$ ./mySigHandler Pid and time print every 3 seconds. Enter Ctrl-C to end the program. PID: 10985 CURRENT TIME: Tue Nov 24 22:00:12 2020 2020/12/19 p6: Signal Handling https://canvas.wisc.edu/courses/205087/assignments/934459 4/10 PID: 10985 CURRENT TIME: Tue Nov 24 22:00:15 2020 PID: 10985 CURRENT TIME: Tue Nov 24 22:00:18 2020 SIGUSR1 handled and counted! PID: 10985 CURRENT TIME: Tue Nov 24 22:00:21 2020 SIGUSR1 handled and counted! PID: 10985 CURRENT TIME: Tue Nov 24 22:00:24 2020 PID: 10985 CURRENT TIME: Tue Nov 24 22:00:27 2020 SIGUSR1 handled and counted! SIGUSR1 handled and counted! PID: 10985 CURRENT TIME: Tue Nov 24 22:00:30 2020 SIGUSR1 handled and counted! PID: 10985 CURRENT TIME: Tue Nov 24 22:00:54 2020 PID: 10985 CURRENT TIME: Tue Nov 24 22:00:57 2020 ^C SIGINT handled. SIGUSR1 was handled 5 times. Exiting now. [deppeler@liederkranz] (67)$ Sending Signals Write a simple program sendsig.c which you can use to send signals (SIGINT and SIGUSR1) to other programs like mySigHandler. You can send signals to other programs by using their pid. For this program, you will need to use the system call kill(). Your sendsig program requires two command line arguments: the first argument indicates the type of signal (-i for SIGINT or -u for SIGUSR1) and the second argument is the pid of the process to which the signal is sent. The output of sendsig should look like the following: [deppeler@liederkranz] (77)$ sendsig Usage: [deppeler@liederkranz] (78)$ sendsig -u 18163 [deppeler@liederkranz] (79)$ sendsig -u 18163 [deppeler@liederkranz] (80)$ sendsig -i 18163 Run your sendsig program with the process id of a running mySigHandler program to see how your mySigHandler program handles the user signals (-u and -i) that you send. Make sure that both programs work as required (shown in examples). For example: 1. Start mySigHandler in a terminal window. 2. Note the pid for the running process and let it run. 3. Open a new terminal window connected to the same machine. 4. Run sendsig with -u and the pid of mySigHandler 5. Check that mySigHandler handles the user signal as required. 6. Try sendsig -u pid a few more times. 7. Then, try sendsig -i pid to end your mySigHandler program. Divide by ZERO 2020/12/19 p6: Signal Handling https://canvas.wisc.edu/courses/205087/assignments/934459 5/10 For the third program, you will add an exception handler that handles divide by 0 exceptions. For this part, write a program, division.c, with an infinite loop that does the following: Prompt for and read in one integer value. Prompt for and read in a second integer value. Calculate the quotient and remainder of doing the integer division operation: int1 / int2 Print the results as shown in the examples that follow. Keep a total count of how many division operations were successfully completed. DO NOT USE fscanf() or scanf() for this assignment. Do use fgets() to read each line of input (use a buffer of 100 bytes). Do use atoi() to translate that C string to an integer. Normally, we’d design our programs to check the user input for validity. For this program we’ll ignore error checking the input. If the user enters a bad integer value, don’t worry about it. Just use whatever value atoi() returns. At this stage the sample run of the program would appear as: [deppeler@liederkranz] (121)$ ls division* division.c [deppeler@liederkranz] (122)$ ./division Enter first integer: 12 Enter second integer: 2 12 / 2 is 6 with a remainder of 0 Enter first integer: 100 Enter second integer: -7 100 / -7 is -14 with a remainder of 2 Enter first integer: 10 Enter second integer: 20 10 / 20 is 0 with a remainder of 10 Enter first integer: ab17 Enter second integer: 3 0 / 3 is 0 with a remainder of 0 Enter first integer: ^C [deppeler@liederkranz] (123)$ Please note the behavior of the program example for a non-numeric input ‘ab17’. Handle similar inputs in the same way. Try giving the input for the second integer as 0. This will cause a divide by zero exception. This arithmetic error that occurs typically causes a program to crash, but we can implement a signal handler to override this default behavior of the SIGFPE signal. Modify your program with a handler that is registered to run if the program receives the SIGFPE signal. In the signal handler you will print a message stating that a divide by 0 operation was attempted, print 2020/12/19 p6: Signal Handling https://canvas.wisc.edu/courses/205087/assignments/934459 6/10 the number of successfully completed division operations, and then gracefully exit the program using exit(0) instead of crashing. Below is a sample output of how your program should behave: [deppeler@liederkranz] (132)$ ./division Enter first integer: 1 Enter second integer: 2 1 / 2 is 0 with a remainder of 1 Enter first integer: 1 Enter second integer: 0 Error: a division by 0 operation was attempted. Total number of operations completed successfully: 1 The program will be terminated. [deppeler@liederkranz] (133)$ As was mentioned above, a global variable is used so that the count of the number of completed divisions can be accessible by both main() and your signal handler. Lastly, your program should have a separate handler for the keyboard interrupt Ctrl+c just like the mySigHandler.c program did. Except in this program on the first Ctrl+c signal, the handler should print the number of successfully completed division operations, and then exit the program using exit(0). Here is the sample output for division.c that shows the graceful exit of the program in case of a SIGINT signal. [deppeler@liederkranz] (143)$ ./division Enter first integer: 1 Enter second integer: 2 1 / 2 is 0 with a remainder of 1 Enter first integer: 3 Enter second integer: 4 3 / 4 is 0 with a remainder of 3 Enter first integer: ^C Total number of operations completed successfully: 2 The program will be terminated. [deppeler@liederkranz] (144)$ Note: Implement two independent handlers; do not combine the handlers. Do not place the calls to sigaction() within the loop! These calls should be completed before entering the loop that requests and does division on the two integers. REQUIREMENTS Your program must follow style guidelines as given in the Style Guide. Since you will be creating the entire source files on your own, style will count for more points on this assignment. Your program must follow commenting guidelines as given in the Commenting Guide. Since you will be creating the entire source files on your own, commenting will count for more points on this assignment. Your programs should operate exactly as the sample outputs shown above. 2020/12/19 p6: Signal Handling https://canvas.wisc.edu/courses/205087/assignments/934459 7/10 Project p6 f20 We will compile each of your programs with gcc -Wall -m32 -std=gnu99 on the Linux lab machines. So, your programs must compile there, and without warnings or errors. Your program must print error messages, as described and shown in the sample runs above. SUBMITTING Your Work SUBMISSION HAS BEEN ENABLED. Leave plenty of time before the deadline to complete the two steps for submission found below. There is a 24 hour grace period after the deadline for emergencies. Submitting during this grace period results in your submission being marked late but it will be accepted for grading without penalty. No submissions or updates to submissions are accepted after this grace period. 1.) Submit only the files listed below under Project p6 in Assignments on Canvas as a single submission. Do not zip, compress, submit your files in a folder, or submit each file individually. mySigHandler.c sendsig.c division.c Repeated Submission: You may resubmit your work repeatedly so we strongly encourage you to use Canvas to store a backup of your current work. If you resubmit, Canvas will modify your file names by appending a hyphen and a number (e.g., mySigHandler-1.c). 2.) Verify your submission to ensure it is complete and correct. If not, resubmit all of your work rather than updating just some of the files. Make sure you have submitted all the files listed above. Forgetting to submit or not submitting one or more of the listed files will result in you losing credit for the assignment. Make sure the files that you have submitted have the correct contents. Submitting the wrong version of your files, empty files, skeleton files, executable files, corrupted files, or other wrong files will result in you losing credit for the assignment. Make sure your file names exactly match those listed above. If you resubmit your work, Canvas will modify your file names as mentioned in Repeated Submission above. These Canvas modified names are accepted for grading. 2020/12/19 p6: Signal Handling https://canvas.wisc.edu/courses/205087/assignments/934459 8/10 Criteria Ratings Pts 5.0 pts 5.0 pts 5.0 pts 6.0 pts 6.0 pts 6.0 pts 3.0 pts 1.0 pts 1.0 pts 1.0 pts 1.0 pts 1a. mySigHandler.c: Compilation gcc mySigHandler.c -Wall -m32 – std=gnu99 -o mySigHandler 5.0 pts No Errors or Warnings 3.0 pts Compiler Warnings (no errors) 0.0 pts Compiler Errors 1b. sendsig.c: Compilation gcc sendsig.c -Wall -m32 -std=gnu99 -o sendsig 5.0 pts No Errors or Warnings 3.0 pts Compiler Warnings (no errors) 0.0 pts Compiler Errors 1c. division.c: Compilation gcc division.c -Wall -m32 -std=gnu99 -o division 5.0 pts No Errors or Warnings 3.0 pts Compiler Warnings (no errors) 0.0 pts Compiler Errors 2a. mySigHandler.c: Style and Commenting 6.0 to >5.0 pts Excellent 5.0 to >0.0 pts Incomplete 0.0 pts Doesn’t Follow Guides 2b. sendsig.c: Style and Commenting 6.0 to >5.0 pts Excellent 5.0 to >0.0 pts Incomplete 0.0 pts Doesn’t Follow Guides 2c. division.c: Style and Commenting 6.0 to >5.0 pts Excellent 5.0 to >0.0 pts Incomplete 0.0 pts Doesn’t Follow Guides 3a. mySigHandler.c & division.c: sigaction Return Value 3.0 pts Always Checked 2.0 pts Mostly Checked 1.0 pts Sometimes Checked 0.0 pts Never Checked 3b. mySigHandler.c: time Return Value 1.0 pts Always Checked 0.0 pts Not Always Checked 3c. mySigHandler.c: ctime Return Value 1.0 pts Always Checked 0.0 pts Not Always Checked 3d. sendsig.c: kill Return Value 1.0 pts Always Checked 0.0 pts Not Always Checked 3e. division.c: fgets Return Value 1.0 pts Always Checked 0.0 pts Not Always Checked 2020/12/19 p6: Signal Handling https://canvas.wisc.edu/courses/205087/assignments/934459 9/10 Criteria Ratings Pts 5.0 pts 4.0 pts 4.0 pts 5.0 pts 4.0 pts 4.0 pts 5.0 pts 4.0 pts 5.0 pts 4.0 pts 4a. mySigHandler.c & division.c: sigaction Setup and Use struct sigaction setup properly; sigaction() called with proper args (signal() not used); freed if struct sigaction on heap 5.0 to >4.0 pts Correct 4.0 to >0.0 pts Some Issues 0.0 pts Used signal Instead 4b. mySigHandler.c & division.c: sigaction() Call 4.0 pts In main() Before Loop 0.0 pts In Loop or Signal Handlers 5a. mySigHandler.c: main() Infinite Loop 4.0 pts Is Empty 2.0 pts Has Either printf() or alarm() 0.0 pts Has BOTH printf() and alarm() 5b. mySigHandler.c: SIGALRM Handler prints the pid and time, also sets another alarm 5.0 pts Works as Specified 3.0 pts Partially Works 0.0 pts Doesn’t Work 5c. mySigHandler.c: SIGUSR1 Handler prints a message and increments a counter 4.0 pts Works as Specified 2.0 pts Partially Works 0.0 pts Doesn’t Work 5d. mySigHandler.c: SIGINT Handler prints the counter and exits 4.0 pts Works as Specified 2.0 pts Patially Works 0.0 pts Doesn’t Work 6a. sendsig.c: Arguments checked argc for correct number; parsed argv correctly 5.0 pts Works as Specified 3.0 pts Partially Works 0.0 pts Doesn’t Work 6b. sendsig.c: Sends Signal 4.0 pts Sent to Correct Process 0.0 pts Doesn’t Work 7. division.c: main() Loop reads 2 integers and displays quotient and remainder 5.0 pts Works as Specified 3.0 pts Partially Works 0.0 pts Doesn’t Work 8a. division.c: SIGFPE Handler prints number of successful divisions and exits 4.0 pts Works as Specified 2.0 pts Partially Works 0.0 pts Doesn’t Work 2020/12/19 p6: Signal Handling https://canvas.wisc.edu/courses/205087/assignments/934459 10/10 Total Points: 90.0 Criteria Ratings Pts 2.0 pts 4.0 pts 8b. division.c: SIGFPE Handler Error Message 2.0 pts Printed 0.0 pts Not Printed 8c. division.c: SIGINT Handler prints number of successful divisions and exits 4.0 pts Works as Specified 2.0 pts Partially Works 0.0 pts Doesn’t Work
