/*-------------------------------------------------------------------------*
*--- ---*
*--- selfCaller.c ---*
*--- ---*
*--- This program demonstrates process programming and ---*
*--- signalling by "recursively" calling itself a limited number of ---*
*--- and selectively signally its parent process. ---*
*--- ---*
*--- ---- ---- ---- ---- ---- ---- ---- ---- ---*
*--- ---*
*--- Version 1a Joseph Phillips ---*
*--- ---*
*-------------------------------------------------------------------------*/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
const int TEXT_LEN = 16;
const int NUM_SECS_TO_RUN = 30;
#define PROGNAME "selfCaller"
int numTimesCalled[3] = { 0, 0, 0 };
pid_t pidToSignal = -1;
pid_t childPid = -1;
int level = +2;
int shouldRun = 1;
// YOUR SIGNAL HANDLERS HERE
void sigAlarmHandler(int sigNum)
{
printf("Process %d: called level 0\n", level);
alarm(rand() % 10 + 1);
numTimesCalled[0]++;
if (level != 2)
{
kill(pidToSignal, 10);
}
}
void sigUser1Handler(int sigNum)
{
printf("Process %d: called level 1\n", level);
numTimesCalled[1]++;
if (level != 2)
{
kill(pidToSignal, 12);
}
}
void sigUser2Handler(int sigNum)
{
printf("Process %d: called level 2\n", level);
numTimesCalled[2]++;
}
void sigIntHandler(int sigNum)
{
alarm(0);
shouldRun = 0;
}
int main(int argc, char *argv[])
{
srand(getpid());
// YOUR CODE HERE
// 3a - check command line args and set level
if (argc > 1 && (strcmp(argv[1], "0") == 0 || strcmp(argv[1], "1") == 0))
{
level = atoi(argv[1]);
}
else
{
level = 2;
}
// 3b - recursively call program
if (level > 0)
{
childPid = fork();
if (childPid == 0)
{
char text[TEXT_LEN];
snprintf(text, TEXT_LEN, "%d", level - 1);
execl(PROGNAME, PROGNAME, text, NULL);
fprintf(stderr, "Cannot find %s\n", PROGNAME);
exit(EXIT_FAILURE);
}
}
// 3c - install signal handlers
struct sigaction act;
memset(&act, '\0', sizeof(act));
act.sa_handler = sigAlarmHandler;
sigaction(SIGALRM, &act, NULL);
act.sa_handler = sigUser1Handler;
sigaction(SIGUSR1, &act, NULL);
act.sa_handler = sigUser2Handler;
sigaction(SIGUSR2, &act, NULL);
act.sa_handler = sigIntHandler;
sigaction(SIGINT, &act, NULL);
// 3d - send alarm at specified interval
alarm(rand() % 10 + 1);
// 3e - code copied from assignment
if (level == 2)
{
int i;
for (i = 0; i < NUM_SECS_TO_RUN; i++)
{
sleep(1);
}
}
else
{
pidToSignal = getppid();
while (shouldRun)
{
sleep(1);
}
}
// 3f - send SIGINT to child and wait for child
if (childPid > 0)
{
kill(childPid, 2);
wait(NULL);
}
// 3g - code copied from assignment
printf("Level %d: %d %d %d\n", level,
numTimesCalled[0], numTimesCalled[1], numTimesCalled[2]
);
return (EXIT_SUCCESS);
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C language is one of the most popular general-purpose programming language developed by Dennis Ritchie at Bell laboratories for UNIX operating system. The initial release of C Language was in the year 1972. Most of the desktop operating systems are written in C Language.
When ever you want to perform a set of operations based on a condition if-else is used.
if(conditional-expression) {
// code
} else {
// code
}
You can also use if-else for nested Ifs and if-else-if ladder when multiple conditions are to be performed on a single variable.
Switch is an alternative to if-else-if ladder.
switch(conditional-expression) {
case value1:
// code
break; // optional
case value2:
// code
break; // optional
...
default:
// code to be executed when all the above cases are not matched;
}
For loop is used to iterate a set of statements based on a condition.
for(Initialization; Condition; Increment/decrement){
// code
}
While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.
while(condition) {
// code
}
Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.
do {
// code
} while (condition);
Array is a collection of similar data which is stored in continuous memory addresses. Array values can be fetched using index. Index starts from 0 to size-1.
data-type array-name[size];
data-type array-name[size][size];
Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity.
Two types of functions are present in C
Library functions are the in-built functions which are declared in header files like printf(),scanf(),puts(),gets() etc.,
User defined functions are the ones which are written by the programmer based on the requirement.
return_type function_name(parameters);
function_name (parameters)
return_type function_name(parameters) {
//code
}