Write a program that tests the existence of a lock on a file. Use the program writelock-

afile.c to lock a file. When there is a lock on a file, your program (testlock.c) should print the ID of the process holding the lock. Otherwise, it prints the message File is not locked.

C language under Linux

For example, in one window do: $ touch test-file $ ./writelockafile test-file my pid is 5166 locking locked; hit enter to unlock... In another window, run: $ ./testlock test-file File is locked by 5166 When the file is not locked, you should get: $ ./testlock test-file File is not locked For a non-existent file, you should get: ./testlock non-existent-file *** No such file or directory

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writelockafile.c:

#include #include #include #include

/* Creates a write lock on a file */ int main (int argc, char* argv[]) { char* file = argv[1]; int fd; struct flock lock;

printf ("my pid is %d ", (int) getpid ());

printf ("opening %s ", file); /* Open a file descriptor to the file */ fd = open (file, O_WRONLY); printf ("locking "); /* Initialize the flock structure */ memset (&lock, 0, sizeof(lock)); lock.l_type = F_WRLCK; /* Place a write lock on the file */ fcntl (fd, F_SETLKW, &lock);

printf ("locked; hit enter to unlock... "); /* Wait for the user to hit enter */ getchar ();

printf ("unlocking "); /* Release the lock */ lock.l_type = F_UNLCK; fcntl (fd, F_SETLKW, &lock);

close (fd); return 0; }

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Makefile:

all: writelockafile.o cc -o writelockafile writelockafile.o

writelockafile.o: writelockafile.c cc -c writelockafile.c

clean: rm -f *.o writelockafile