How to lock django command for single run. Django. Python.

Question

How to lock django commands so it will not run twise in the same time?

Answer 1

Create a lock somewhere - I recently saw very simple lock implementation that used cache:

LOCK_EXPIRE = 60 * 5

lock_id = "%s-lock-%s" % (self.name, id_hexdigest) #computed earlier

is_locked = lambda: str(cache.get(lock_id)) == "true"
acquire_lock = lambda: cache.set(lock_id, "true", LOCK_EXPIRE)
release_lock = lambda: cache.set(lock_id, "nil", 1)

if not is_locked():
    aquire_lock()
    try:
        #do something
    finally:
        release_lock()

It's just one of many possible implementations.

Edit: Corrected, I just pasted code without thinking. try...finally block is used to ensure that lock is always released, no matter what happens - but of course if statement is also necessary.

Answer 2

There are a bunch of different ways to do this. cji's method looks like it'd work just fine. One thing I tend to do is if my background jobs are operating on model objects, I use status fields to determine if the job can run.

class BookModel(models.Model):
    status_choices = ((1, 'new'), ('2', 'processed'))
    name = models.CharField(max_length=12)
    status = models.CharField(max_length=12, choices=status_choices)

Then if I'm performing something on those books I can do something like so:

if book.status is 1:
    ## do something