RuntimeError when using Theano shared variable in a Celery celery worker

Question

I have a Celery task called simple_theano_tasks:

@app.task(bind=True, queue='test')
def simple_theano_tasks(self):
  import theano, numpy as np
  my_array = np.zeros((0,), dtype=theano.config.floatX)
  shared = theano.shared(my_array, name='my_variable', borrow=True)
  print 'Done. Shared value is {}'.format(shared.get_value())

---

When THEANO is configured to use the CPU, everything works as expected (no error):

$ THEANO_FLAGS=device=cpu celery -A my_project worker -c1 -l info -Q test
[INFO/MainProcess] Received task: my_project.tasks.simple_theano_tasks[xxxx]
[WARNING/Worker-1] Done. Shared value is []
[INFO/MainProcess] Task my_project.tasks.simple_theano_tasks[xxxx] succeeded in 0.00407959899985s

---

Now, when I do the exact same thing with GPU enabled, Theano (or CUDA) raise an error:

$ THEANO_FLAGS=device=gpu celery -A my_project worker -c1 -l info -Q test

 ...

 Using gpu device 0: GeForce GTX 670M (CNMeM is enabled)

 ...

[INFO/MainProcess] Received task: my_project.tasks.simple_theano_tasks[xxx]
[ERROR/MainProcess] Task my_project.tasks.simple_theano_tasks[xxx] raised unexpected: RuntimeError("Cuda error 'initialization error' while copying %lli data element to device memory",)
Traceback (most recent call last):
  File "/.../local/lib/python2.7/site-packages/celery/app/trace.py", line 240, in trace_task
R = retval = fun(*args, **kwargs)
  File "/.../local/lib/python2.7/site-packages/celery/app/trace.py", line 438, in __protected_call__
return self.run(*args, **kwargs)
  File "/.../my_project/tasks.py", line 362, in simple_theano_tasks
shared = theano.shared(my_array, name='my_variable', borrow=True)
  File "/.../local/lib/python2.7/site-packages/theano/compile/sharedvalue.py", line 247, in shared
allow_downcast=allow_downcast, **kwargs)
  File "/.../local/lib/python2.7/site-packages/theano/sandbox/cuda/var.py", line 229, in float32_shared_constructor
deviceval = type_support_filter(value, type.broadcastable, False, None)
RuntimeError: Cuda error 'initialization error' while copying %lli data element to device memory

---

Finally, when I run the exact same code in a Python shell I have no error:

$ THEANO_FLAGS=device=gpu python
Python 2.7.6 (default, Mar 22 2014, 22:59:56) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import theano, numpy as np
Using gpu device 0: GeForce GTX 670M (CNMeM is enabled)
>>> my_array = np.zeros((0,), dtype=theano.config.floatX)
>>> shared = theano.shared(my_array, name='my_variable', borrow=True)
>>> print 'Done. Shared value is {}'.format(shared.get_value())
Done. Shared value is []

---

Does anyone has an idea of:

• Why does theano behave differently inside a Celery worker?
• How to fix this?

---

Some additional context:

• I am using [email protected] and [email protected]

• "~/.theanorc" file

  [global]
  floatX=float32
  device=gpu
  
  [mode]=FAST_RUN
  
  [nvcc]
  fastmath=True
  
  [lib]
  cnmem=0.1
  
  [cuda]
  root=/usr/local/cuda
  

Answer 1

A workaround is to:

1. Specify the CPU as the target device (in ".theanorc" or using "THEANO_FLAGS=device=cpu")
2. Later, override the assigned device to a specified GPU

---

Celery task is now:

@app.task(bind=True, queue='test')
def simple_theano_tasks(self):
  # At this point, no theano import statements have been processed, and so the device is unbound
  import theano, numpy as np
  import theano.sandbox.cuda
  theano.sandbox.cuda.use('gpu') # enable gpu
  my_array = np.zeros((0,), dtype=theano.config.floatX)
  shared = theano.shared(my_array, name='my_variable', borrow=True)
  print 'Done. Shared value is {}'.format(shared.get_value())

---

Note: I found the solution reading this article about using multiple GPU