Linux Posix Timer

linux_posix_timer/cleaner.sh

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+rm *~ .*

linux_posix_timer/compile.sh

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+gcc -c timerexample.c -o timerexample.o
+gcc timerexample.o -o timerexample.exe -lrt
+rm *.o

linux_posix_timer/timerexample.c

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+/*
+ * =====================================================================================
+ *
+ *       Filename:  timerExample.c
+ *
+ *    Description: This file demonstrates the use of POSIX Timer routines
+ *
+ *        Version:  1.0
+ *        Created:  10/12/2020 11:25:06 AM
+ *       Revision:  none
+ *       Compiler:  gcc
+ *
+ *         Author:  ABHISHEK SAGAR (), sachinites@gmail.com
+ *   Organization:  Juniper Networks
+ *
+ * =====================================================================================
+ */
+
+#include <signal.h>
+#include <time.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <memory.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+/* Example */
+
+void
+print_current_system_time(){
+    time_t t;
+    time(&t); /* Get the current time of the system */
+    printf("%s ",ctime(&t));
+}
+
+
+typedef struct pair_{
+
+	int a;
+	int b;
+} pair_t;
+
+pair_t pair = { 10, 20 };
+
+
+/* The Timer callback function which will be called every
+ * time the timer expires. The signature of the function would be :
+ * void <fn-name>(union sigval)
+ * */
+void
+timer_callback(union sigval arg){
+
+    print_current_system_time();
+
+	pair_t *pair = (pair_t *)(arg.sival_ptr); /* extract the user data structure */
+    
+    printf("pair : [%u %u]", pair->a, pair->b );
+}
+
+void
+timer_demo(){
+
+	int ret;
+	timer_t timer;
+	struct sigevent evp;
+    
+    memset(&timer,0,sizeof(timer));
+
+	/* evp variable is used to setup timer properties*/
+	memset(&evp, 0, sizeof(struct sigevent));
+	
+    /* Fill the user defined data structure.
+     * When timer expires, this will be passed as
+     * argument to the timer callback handler */
+	evp.sigev_value.sival_ptr = (void *)&pair;
+
+	/* On timer Expiry, We want kernel to launch the
+ 	 * timer handler routine in a separate thread context */
+	evp.sigev_notify = SIGEV_THREAD;
+	
+	/* Register the timer hander routine. This routine shall
+ 	 * be invoked when timer expires*/
+	evp.sigev_notify_function = timer_callback; 
+
+	/* Create a timer. It is just a timer initialization, Timer
+ 	 * is not fired (Alarmed)  */
+	ret = timer_create (CLOCK_REALTIME,
+						&evp,
+						&timer);
+
+	if ( ret < 0) {
+		
+		printf("Timer Creation failed, errno = %d\n", errno);
+		exit(0);
+	}
+
+	/* Let us say, I want to start the timer after 5 seconds from now
+ 	 * (now =  say, t = 0) and once the 5 seconds elapsed, i 
+ 	 * want the timer to keep firing after every 2 seconds repeatedly.
+ 	 * It simply mean that - if i start the timer as time t = 0, then
+ 	 * timer handler routine (timer_callback) shall be called at t = 5,
+ 	 * t = 7, t = 9 ... so on*/
+
+	/* Let us setup the time intervals */
+
+	struct itimerspec ts;
+
+	/* I want the timer to fire for the first time after 5 seconds
+ 	 * and 0 nano seconds*/
+	ts.it_value.tv_sec = 5;
+	ts.it_value.tv_nsec = 0;
+
+	/* After the timer has fired for the first time, i want the timer
+ 	 * to repeatedly fire after every 2 sec and 0 nano sec */
+	ts.it_interval.tv_sec = 2;
+	ts.it_interval.tv_nsec = 0;
+
+	/* Now start the timer*/
+	ret = timer_settime (timer,
+						 0,
+						 &ts,
+						 NULL);
+
+	if ( ret < 0) {
+		
+		printf("Timer Start failed, errno = %d\n", errno);
+		exit(0);
+	}
+    else{
+        print_current_system_time();
+        printf("Timer Alarmed Successfully\n");
+    }
+}
+
+int
+main(int argc, char **argv){
+
+	timer_demo();
+	pause();
+	return 0;
+}