This code is about.
Race conditions: Scheduling and compiler behaviour play a significant role in process or thread synchronization. The simplest scenario to demonstrate the need to synchronization comes from the race conditions created between two threads/process trying to modify a value of a shared variable, which typically results in data inconsistency, and erroneous results. The following example demonstrates this situation:
I'm new to C and am having trouble with what is happening with this warning. What does the warning mean and how can i fix it. The code i wrote is here:
q1.c: In function ‘runner’:
q1.c:13:1: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘long int’ [-Wformat=]
printf("T tid: %d x before: %d\n", syscall(SYS_gettid),x); int i;
^
q1.c:19:1: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘long int’ [-Wformat=]
printf("T tid: %d x after: %d\n", syscall(SYS_gettid),x);
Here's the code:
// Race condition
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/syscall.h>
int x=0;
void * runner(void *arg)
{
printf("T tid: %d x before: %d\n", syscall(SYS_gettid),x); int i;
for (i = 0; i < 100000; i++ )
{
x = x + 1;
}
printf("T tid: %d x after: %d\n", syscall(SYS_gettid),x);
}
int program()
{
pthread_t t1,t2,t3,t4;
printf("Parent pid: %d x before threads: %d\n", getpid(),x); int i;
if(pthread_create(&t1,NULL, runner, NULL)){ printf("Error creating thread 1\n"); return 1;
}
if(pthread_create(&t2,NULL, runner, NULL)){ printf("Error creating thread 2\n"); return 1;
}
if(pthread_create(&t3,NULL, runner, NULL)){ printf("Error creating thread 1\n"); return 1;
}
if(pthread_create(&t4,NULL, runner, NULL)){ printf("Error creating thread 1\n"); return 1;
}
if(pthread_join(t1,NULL)){ printf("error joining thread 1"); return 1;
}
if(pthread_join(t2,NULL)){ printf("error joining thread 1"); return 1;
}
if(pthread_join(t3,NULL)){ printf("error joining thread 1"); return 1;
}
if(pthread_join(t4,NULL)){ printf("error joining thread 1"); return 1;
}
printf("Parent pid: %d x after threads: %d\n", getpid(),x); return 0;
}
int main(int argc, char *argv[]) {
int count=0;
// loop runs the program count times
while(count<5)
{
// running program program();
count++;
//reset global x for next run of program. x=0;
printf("\n\n");
}
return 0;
}
You have to change "%d"
with "%ld"
, "%d"
is for signed int
and here the l
stands for long
so "%ld"
is for signed long int
.