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Computers and Technology, 27.10.2020 23:00 help445492
In the example program below, a variable is used to protect the critical section. Why did it fail? Use pthread_mutex_init( ) and pthread_mutex_lock( )/pthread_mutex_unlock( ) system call to modify this program so that the result is correct.
// when input thread number to be 100
// then two output are different
#include
#include
char USAGE[] = "naive_lock n_threads\n"
"USAGE: run n threads with a naive lock\n";
int lock = 0; //0 for unlocked, 1 for locked
int shared = 0; //shared variable
void * incrementer(void * args){
int i;
for(i=0;i 0); //spin until unlocked
lock = 1; //set lock
shared++; //increment
lock = 0; //unlock
}
return NULL;
}
int main(int argc, char * argv[]){
pthread_t * threads;
int n, i;
if(argc < 2){
fprintf(stderr, "USAGE: program number_of_thread\n");
exit(1);
}
//convert argv[1] to a long
if((n = atol(argv[1])) == 0){
fprintf(stderr, "ERROR: Invalid number of threads\n");
exit(1);
}
//allocate array of pthread_t identifiers
threads = calloc(n, sizeof(pthread_t));
//create n threads
for(i=0;i
pthread_create(&threads[i], NULL, incrementer, NULL);
}
//join all threads
for(i=0;i
pthread_join(threads[i], NULL);
}
//print shared value and result
printf("Shared: %d\n",shared);
printf("Expect: %d\n",n*100);
return 0;
}
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