inline void remove_if_can_lock_file(const char *file_path)
{
file_handle_t fhnd = open_existing_file(file_path, read_write);
if(fhnd != invalid_file()){
bool acquired;
if(try_acquire_file_lock(fhnd, acquired) && acquired){
delete_file(file_path);
}
close_file(fhnd);
}
}
robust_mutex_lock_file()
{
permissions p;
p.set_unrestricted();
//Remove old lock files of other processes
remove_old_robust_lock_files();
//Create path and obtain lock file path for this process
create_and_get_robust_lock_file_path(fname, get_current_process_id());
//Now try to open or create the lock file
fd = create_or_open_file(fname.c_str(), read_write, p);
//If we can't open or create it, then something unrecoverable has happened
if(fd == invalid_file()){
throw interprocess_exception(other_error, "Robust emulation robust_mutex_lock_file constructor failed: could not open or create file");
}
//Now we must take in care a race condition with another process
//calling "remove_old_robust_lock_files()". No other threads from this
//process will be creating the lock file because intermodule_singleton
//guarantees this. So let's loop acquiring the lock and checking if we
//can't exclusively create the file (if the file is erased by another process
//then this exclusive open would fail). If the file can't be exclusively created
//then we have correctly open/create and lock the file. If the file can
//be exclusively created, then close previous locked file and try again.
while(1){
bool acquired;
if(!try_acquire_file_lock(fd, acquired) || !acquired ){
throw interprocess_exception(other_error, "Robust emulation robust_mutex_lock_file constructor failed: try_acquire_file_lock");
}
//Creating exclusively must fail with already_exists_error
//to make sure we've locked the file and no one has
//deleted it between creation and locking
file_handle_t fd2 = create_new_file(fname.c_str(), read_write, p);
if(fd2 != invalid_file()){
close_file(fd);
fd = fd2;
continue;
}
//If exclusive creation fails with expected error go ahead
else if(error_info(system_error_code()).get_error_code() == already_exists_error){ //must already exist
//Leak descriptor to mantain the file locked until the process dies
break;
}
//If exclusive creation fails with unexpected error throw an unrecoverable error
else{
close_file(fd);
throw interprocess_exception(other_error, "Robust emulation robust_mutex_lock_file constructor failed: create_file filed with unexpected error");
}
}
}
inline bool robust_spin_mutex<Mutex>::is_owner_dead(boost::uint32_t own)
{
//If owner is an invalid id, then it's clear it's dead
if(own == (boost::uint32_t)get_invalid_process_id()){
return true;
}
//Obtain the lock filename of the owner field
std::string file;
this->owner_to_filename(own, file);
//Now the logic is to open and lock it
file_handle_t fhnd = open_existing_file(file.c_str(), read_write);
if(fhnd != invalid_file()){
//If we can open the file, lock it.
bool acquired;
if(try_acquire_file_lock(fhnd, acquired) && acquired){
//If locked, just delete the file
delete_file(file.c_str());
close_file(fhnd);
return true;
}
//If not locked, the owner is suppossed to be still alive
close_file(fhnd);
}
else{
//If the lock file does not exist then the owner is dead (a previous cleanup)
//function has deleted the file. If there is another reason, then this is
//an unrecoverable error
if(error_info(system_error_code()).get_error_code() == not_found_error){
return true;
}
}
return false;
}
/*
* osprd_ioctl(inode, filp, cmd, arg)
* Called to perform an ioctl on the named file.
*/
int osprd_ioctl(struct inode *inode, struct file *filp,
unsigned int cmd, unsigned long arg)
{
osprd_info_t *d = file2osprd(filp); // device info
int r = 0; // return value: initially 0
// Set 'r' to the ioctl's return value: 0 on success, negative on error
if (cmd == OSPRDIOCACQUIRE) {
// EXERCISE: Lock the ramdisk.
//
// If *filp is open for writing (filp_writable), then attempt
// to write-lock the ramdisk; otherwise attempt to read-lock
// the ramdisk.
//
// This lock request must block using 'd->blockq' until:
// 1) no other process holds a write lock;
// 2) either the request is for a read lock, or no other process
// holds a read lock; and
// 3) lock requests should be serviced in order, so no process
// that blocked earlier is still blocked waiting for the
// lock.
//
// If a process acquires a lock, mark this fact by setting
// 'filp->f_flags |= F_OSPRD_LOCKED'. You also need to
// keep track of how many read and write locks are held:
// change the 'osprd_info_t' structure to do this.
//
// Also wake up processes waiting on 'd->blockq' as needed.
//
// If the lock request would cause a deadlock, return -EDEADLK.
// If the lock request blocks and is awoken by a signal, then
// return -ERESTARTSYS.
// Otherwise, if we can grant the lock request, return 0.
// 'd->ticket_head' and 'd->ticket_tail' should help you
// service lock requests in order. These implement a ticket
// order: 'ticket_tail' is the next ticket, and 'ticket_head'
// is the ticket currently being served. You should set a local
// variable to 'd->ticket_head' and increment 'd->ticket_head'.
// Then, block at least until 'd->ticket_tail == local_ticket'.
// (Some of these operations are in a critical section and must
// be protected by a spinlock; which ones?)
// Used to track the current request
unsigned local_ticket;
if(check_deadlock(d))
return -EDEADLK;
// If we can't acquire the lock we put ourselves in the back of the queue
// when the lock is released ticket_head will be incremented and we'll be
// woken up
while(try_acquire_file_lock(filp) != 0)
{
spin_lock(&d->mutex);
d->ticket_tail++;
local_ticket = d->ticket_tail;
d->lock_waiter_l = list_add_to_front(d->lock_waiter_l, current->pid);
spin_unlock(&d->mutex);
wait_event_interruptible(d->blockq, d->ticket_head == local_ticket || d->num_to_requeue > 0);
spin_lock(&d->mutex);
d->lock_waiter_l = list_remove_element(d->lock_waiter_l, current->pid);
spin_unlock(&d->mutex);
// process any pending signals by re-queueing everything
if(d->num_to_requeue > 0)
{
// Note: do NOT wake threads here, each thread should requeue only ONCE
spin_lock(&d->mutex);
d->num_to_requeue--;
spin_unlock(&d->mutex);
// If we find another pending signal, dispatch that too
if(signal_pending(current))
return -ERESTARTSYS;
}
else if(signal_pending(current)) // See if we were woken up by a signal
{
// For simplicity, we requeue all waiting tasks (-1 which
// is the process) being "popped" off the wait queue
spin_lock(&d->mutex);
d->num_to_requeue = (d->ticket_tail - d->ticket_head - 1);
d->ticket_head = 0;
d->ticket_tail = 0;
// All threads are woken to notify them of requeuing
// meanwhile, we wait until that finishes (no need to check
// for more interrupts, the process will exit anyway).
wake_up_all(&d->blockq);
spin_unlock(&d->mutex);
// Sanity check
if(d->num_to_requeue > 0)
{
wait_event(d->blockq, d->num_to_requeue == 0);
wake_up_all(&d->blockq); // Wake everyone up again to check for other pending signals
}
return -ERESTARTSYS;
}
}
r = 0;
} else if (cmd == OSPRDIOCTRYACQUIRE) {
// EXERCISE: ATTEMPT to lock the ramdisk.
//
// This is just like OSPRDIOCACQUIRE, except it should never
// block. If OSPRDIOCACQUIRE would block or return deadlock,
// OSPRDIOCTRYACQUIRE should return -EBUSY.
// Otherwise, if we can grant the lock request, return 0.
r = try_acquire_file_lock(filp);
if(r == -EDEADLK)
r = -EBUSY;
} else if (cmd == OSPRDIOCRELEASE) {
// EXERCISE: Unlock the ramdisk.
//
// If the file hasn't locked the ramdisk, return -EINVAL.
// Otherwise, clear the lock from filp->f_flags, wake up
// the wait queue, perform any additional accounting steps
// you need, and return 0.
r = release_file_lock(filp);
} else
r = -ENOTTY; /* unknown command */
return r;
}