Remarks#

Define & start the Flow via an explicit function call inside if __name__ == '__main__'. For example

✅ Do

from jina import Flow, Executor, requests

class CustomExecutor(Executor):
    @requests
    def foo(self, **kwargs):
        ...

def main():
    f = Flow().add(uses=CustomExecutor)
    with f:
        ...

if __name__ == '__main__':
    main()

😔 Don’t

from jina import Flow, Executor, requests

class CustomExecutor(Executor):
    @requests
    def foo(self, **kwargs):
        ...

f = Flow().add(uses=CustomExecutor)
with f:
    ...

"""
# error
This probably means that you are not using fork to start your
child processes and you have forgotten to use the proper idiom
in the main module:

    if _name_ == '_main_':
        freeze_support()
        ...

The "freeze_support()" line can be omitted if the program
is not going to be frozen to produce an executable.

"""

Declare Executors on the top-level of the module

✅ Do

class CustomExecutor(Executor):
    @requests
    def foo(self, **kwargs):
        ...

def main():
    f = Flow().add(uses=Executor)
    with f:
        ...

😔 Don’t

def main():
    class CustomExecutor(Executor):
        @requests
        def foo(self, **kwargs):
            ...

    f = Flow().add(uses=Executor)
    with f:
        ...

Always provide absolute path

While passing filepaths to different jina arguments (e.g.- uses, py_modules), always pass the absolute path.

multiprocessing Spawn#

Few cases require to use spawn start method for multiprocessing. (e.g.- Cannot re-initialize CUDA in forked subprocess. To use CUDA with multiprocessing, you must use the ‘spawn’ start method)

Please set JINA_MP_START_METHOD=spawn before starting the Python script to enable this.

Hint

There’s no need to set this for Windows, as it only supports spawn method for multiprocessing.
Avoid un-picklable objects

Here’s a list of types that can be pickled in Python. Since spawn relies on pickling, we should avoid using code that cannot be pickled.
Hint

Here are a few errors which indicates that you are using some code that is not pickable.
```
pickle.PicklingError: Can't pickle: it's not the same object
AssertionError: can only join a started process
```
Inline functions, such as nested or lambda functions are not picklable. Use functools.partial instead.

Debugging Executor in a Flow#

Standard Python breakpoints will not work inside Executor methods when called inside a Flow context manager. Nevertheless, import epdb; epdb.set_trace() will work just as a native python breakpoint. Note that you need to pip install epdb to have acces to this type of breakpoints.

✅ Do

from jina import Flow, Executor, requests
 
class CustomExecutor(Executor):
    @requests
    def foo(self, **kwargs):
        a = 25
        import epdb; epdb.set_trace() 
        print(f'\n\na={a}\n\n')
 
def main():
    f = Flow().add(uses=CustomExecutor)
    with f:
        f.post(on='')

if __name__ == '__main__':
    main()

😔 Don’t

from jina import Flow, Executor, requests
 
class CustomExecutor(Executor):
    @requests
    def foo(self, **kwargs):
        a = 25
        breakpoint()
        print(f'\n\na={a}\n\n')
 
def main():
    f = Flow().add(uses=CustomExecutor)
    with f:
        f.post(on='')
 
if __name__ == '__main__':
    main()