ece282/lab06/lockingappend.c

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/stat.h>

#define MAX_ATTEMPTS 5	// Maximum retry attempts

int main(int argc, char *argv[]) {
	if (argc < 3) {
		fprintf(stderr, "Usage: %s <target_file> \"text to append\"\n", argv[0]);
		return 1;
	}

	char *target_file = argv[1];
	char *text_to_append = argv[2];
	char lock_file[256];

	// Generate lock file name
	snprintf(lock_file, sizeof(lock_file), "%s.LCK", target_file);

	// Check if the target file exists; if not, create it
	struct stat buffer;
	if (stat(target_file, &buffer) != 0) {
		// File does not exist, create it
		printf("Target file does not exist. Creating %s...\n", target_file);
		FILE *file = fopen(target_file, "w");
		if (!file) {
			perror("Error creating file");
			return 1;
		}
		fclose(file);
	}

	int attempts = 0;

	while (attempts < MAX_ATTEMPTS) {
		if (link(target_file, lock_file) == 0) {
			// Link created successfully
			printf("Lock acquired: %s\n", lock_file);

			FILE *file = fopen(target_file, "a");
			if (file) {
				fprintf(file, "%s\n", text_to_append);
				fclose(file);
				printf("Text appended to %s\n", target_file);
			} else {
				perror("fopen");
			}

			// used for debugging
			// sleep(5);
			unlink(lock_file);
			// Remove the lock
			printf("Lock released: %s\n", lock_file);
			return 0;
		} else {
			perror("link");
			sleep(1);
			attempts++;
		}
	}

	printf("Failed to acquire lock after %d attempts.\n", MAX_ATTEMPTS);
	return 1;
}