# How to have just one instance of a dependency?
**URL:** https://discourse.nameko.io/t/how-to-have-just-one-instance-of-a-dependency/170
**Category:** googlegroup
**Created:** [February 10, 2017, 11:32am UTC](https://discourse.nameko.io/t/how-to-have-just-one-instance-of-a-dependency/170 "2017-02-10T11:32:22Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Richard](https://discourse.nameko.io/u/Richard)
#### Post date: [February 10, 2017, 11:32am UTC](https://discourse.nameko.io/t/how-to-have-just-one-instance-of-a-dependency/170/1 "2017-02-10T11:32:22Z")
I'm converting a flask app to a nameko service, in the old flask all there
was a globally instantiated class which takes about 5 seconds to init.
I've refactored this into a nameko dependency, roughly looking like:
class SlowThing:
def \_\_init\_\_(self):
time.sleep(5)
class MyThing(DependencyProvider):
def get\_dependency(self, worker\_ctx):
return SlowThing()
class MyService:
name = 'my\_service'
rivescript = MyThing()
With the above, SlowThing() will be init'd for each request to the service.
What's the best way to have just one instance of SlowThing() upon service
startup? Should I make that class a singleton? Or is there a better
recommended way?
Thanks in advance.
---
### Author:  [@David\_Szotten](https://discourse.nameko.io/u/David_Szotten)
#### Post date: [February 10, 2017, 11:36am UTC](https://discourse.nameko.io/t/how-to-have-just-one-instance-of-a-dependency/170/2 "2017-02-10T11:36:05Z")
Hi Richard,
Following the example in e.g.
[https://github.com/onefinestay/nameko-sqlalchemy/blob/master/nameko\_sqlalchemy/database\_session.py](https://github.com/onefinestay/nameko-sqlalchemy/blob/master/nameko_sqlalchemy/database_session.py)
you can instantiate your SlowThing in `MyThing.setup()`, and attach it to
self, and then give workers access to that from `get_dependency` (note that
this requires `SlowThing` instances to be threadsafe, i.e. safe for sharing
by multiple concurrent workers)
Best,
David
> **···**
>
> On Friday, 10 February 2017 11:32:23 UTC, Richard wrote:
>
> > I'm converting a flask app to a nameko service, in the old flask all there
> > was a globally instantiated class which takes about 5 seconds to init.
> >
> > I've refactored this into a nameko dependency, roughly looking like:
> >
> > class SlowThing:
> > def \_\_init\_\_(self):
> > time.sleep(5)
> >
> > class MyThing(DependencyProvider):
> >
> > def get\_dependency(self, worker\_ctx):
> > return SlowThing()
> >
> > class MyService:
> > name = 'my\_service'
> > rivescript = MyThing()
> >
> > With the above, SlowThing() will be init'd for each request to the
> > service.
> >
> > What's the best way to have just one instance of SlowThing() upon service
> > startup? Should I make that class a singleton? Or is there a better
> > recommended way?
> >
> > Thanks in advance.
---
### Author:  [@Richard](https://discourse.nameko.io/u/Richard)
#### Post date: [February 10, 2017, 11:37am UTC](https://discourse.nameko.io/t/how-to-have-just-one-instance-of-a-dependency/170/3 "2017-02-10T11:37:37Z")
Perfect thanks. And yes it's thread safe
> **···**
>
> On Friday, February 10, 2017 at 11:36:06 AM UTC, David Szotten wrote:
>
> > Hi Richard,
> >
> > Following the example in e.g.
> > [https://github.com/onefinestay/nameko-sqlalchemy/blob/master/nameko\_sqlalchemy/database\_session.py](https://github.com/onefinestay/nameko-sqlalchemy/blob/master/nameko_sqlalchemy/database_session.py)
> > you can instantiate your SlowThing in `MyThing.setup()`, and attach it to
> > self, and then give workers access to that from `get_dependency` (note that
> > this requires `SlowThing` instances to be threadsafe, i.e. safe for sharing
> > by multiple concurrent workers)
> >
> > Best,
> > David
> >
> > On Friday, 10 February 2017 11:32:23 UTC, Richard wrote:
> >
> > > I'm converting a flask app to a nameko service, in the old flask all
> > > there was a globally instantiated class which takes about 5 seconds to init.
> > >
> > > I've refactored this into a nameko dependency, roughly looking like:
> > >
> > > class SlowThing:
> > > def \_\_init\_\_(self):
> > > time.sleep(5)
> > >
> > > class MyThing(DependencyProvider):
> > >
> > > def get\_dependency(self, worker\_ctx):
> > > return SlowThing()
> > >
> > > class MyService:
> > > name = 'my\_service'
> > > rivescript = MyThing()
> > >
> > > With the above, SlowThing() will be init'd for each request to the
> > > service.
> > >
> > > What's the best way to have just one instance of SlowThing() upon
> > > service startup? Should I make that class a singleton? Or is there a better
> > > recommended way?
> > >
> > > Thanks in advance.