Futures — Anaconda Enterprise 4.4 documentation

Anaconda Enterprise: Documentation

# Futures

Dask supports a real-time task framework that extends Python’s concurrent.futures interface. This interface is good for arbitrary task scheduling, like dask.delayed, but is immediate rather than lazy, which provides some more flexibility in situations where the computations may evolve over time.

These features depend on the second generation task scheduler found in dask.distributed (which, despite its name, runs very well on a single machine).

## Start Dask Client

You must start a `Client` to use the futures interface. This tracks state among the various worker processes or threads.

    from dask.distributed import Client

    client = Client()  # start local workers as processes
    # or
    client = Client(processes=False)  # start local workers as threads

If you have Bokeh installed then this starts up a diagnostic dashboard at http://localhost:8786 .

## Submit Tasks

`Client.submit`(func, \*args, \*\*kwargs) | Submit a function application to the scheduler
`Client.map`(func, \*iterables, \*\*kwargs) | Map a function on a sequence of arguments
`Future.result`([timeout]) | Wait until computation completes, gather result to local process.

Then you can submit individual tasks using the `submit` method.

    def inc(x):
        return x + 1

    def add(x, y):
        return x + y

    a = client.submit(inc, 10)  # calls inc(10) in background thread or process
    b = client.submit(inc, 20)  # calls inc(20) in background thread or process

Submit returns a `Future`, which refers to a remote result. This result may not yet be completed:

    >>> a
    <Future: status: pending, key: inc-b8aaf26b99466a7a1980efa1ade6701d>

Eventually it will complete. The result stays in the remote thread/process/worker until you ask for it back explicitly.

    >>> a
    <Future: status: finished, type: int, key: inc-b8aaf26b99466a7a1980efa1ade6701d>

    >>> a.result()  # blocks until task completes and data arrives
    11

You can pass futures as inputs to submit. Dask automatically handles dependency tracking; once all input futures have completed they will be moved onto a single worker (if necessary), and then the computation that depends on them will be started. You do not need to wait for inputs to finish before submitting a new task; Dask will handle this automatically.

    c = client.submit(add, a, b)  # calls add on the results of a and b

Similar to Python’s `map` you can use `Client.map` to call the same function and many inputs:

    futures = client.map(inc, range(1000))

However note that each task comes with about 1ms of overhead. If you want to map a function over a large number of inputs then you might consider dask.bag or dask.dataframe instead.

## Move Data

`Future.result`([timeout]) | Wait until computation completes, gather result to local process.
`Client.gather`(futures[, errors, maxsize, ...]) | Gather futures from distributed memory
`Client.scatter`(data[, workers, broadcast, ...]) | Scatter data into distributed memory

Given any future you can call the `.result` method to gather the result. This will block until the future is done computing and then transfer the result back to your local process if necessary.

    >>> c.result()
    32

You can gather many results concurrently using the `Client.gather` method. This can be more efficient than calling `.result()` on each future sequentially.

    >>> # results = [future.result() for future in futures]
    >>> results = client.gather(futures)  # this can be faster

If you have important local data that you want to include in your computation you can either include it as a normal input to a submit or map call:

    >>> df = pd.read_csv('training-data.csv')
    >>> future = client.submit(my_function, df)

Or you can `scatter` it explicitly. Scattering moves your data to a worker and returns a future pointing to that data:

    >>> remote_df = client.scatter(df)
    >>> remote_df
    <Future: status: finished, type: DataFrame, key: bbd0ca93589c56ea14af49cba470006e>

    >>> future = client.submit(my_function, remote_df)

Both of these accomplish the same result, but using scatter can sometimes be faster. This is especially true if you use processes or distributed workers (where data transfer is necessary) and you want to use `df` in many computations. Scattering the data beforehand avoids excessive data movement.

Calling scatter on a list scatters all elements individually. Dask will spread these elements evenly throughout workers in a round-robin fashion:

    >>> client.scatter([1, 2, 3])
    [<Future: status: finished, type: int, key: c0a8a20f903a4915b94db8de3ea63195>,
     <Future: status: finished, type: int, key: 58e78e1b34eb49a68c65b54815d1b158>,
     <Future: status: finished, type: int, key: d3395e15f605bc35ab1bac6341a285e2>]

## References, Cancellation, and Exceptions

`Future.cancel`([force]) | Cancel request to run this future
`Future.exception`([timeout]) | Return the exception of a failed task
`Future.traceback`([timeout]) | Return the traceback of a failed task
`Client.cancel`(futures[, asynchronous, force]) | Cancel running futures

Dask will only compute and hold onto results for which there are active futures. In this way your local variables define what is active in Dask. When a future is garbage collected by your local Python session, Dask will feel free to delete that data or stop ongoing computations that were trying to produce it.

    >>> del future  # deletes remote data once future is garbage collected

You can also explicitly cancel a task using the `Future.cancel` or `Client.cancel` methods.

    >>> future.cancel()  # deletes data even if other futures point to it

If a future fails, then Dask will raise the remote exceptions and tracebacks if you try to get the result.

    def div(x, y):
        return x / y

    >>> a = client.submit(div, 1, 0)  # 1 / 0 raises a ZeroDivisionError
    >>> a
    <Future: status: error, key: div-3601743182196fb56339e584a2bf1039>

    >>> a.result()
          1 def div(x, y):
    ----> 2     return x / y

    ZeroDivisionError: division by zero

All futures that depend on an erred future also err with the same exception:

    >>> b = client.submit(inc, a)
    >>> b
    <Future: status: error, key: inc-15e2e4450a0227fa38ede4d6b1a952db>

You can collect the exception or traceback explicitly with the `Future.exception` or `Future.traceback` methods.

## Waiting on Futures

`as_completed`([futures, loop, with_results]) | Return futures in the order in which they complete
`wait`(fs[, timeout, return_when]) | Wait until all futures are complete

You can wait on a future or collection of futures using the `wait` function:

    from dask.distributed import wait

    >>> wait(futures)

This blocks until all futures are finished or have erred.

You can also iterate over the futures as they complete using the `as_completed` function:

    from dask.distributed import as_completed

    futures = client.map(score, x_values)

    best = -1
    for future in as_completed(futures):
       y = future.result()
       if y > best:
           best = y

For greater efficiency you can also ask `as_completed` to gather the results in the background.

    for future in as_completed(futures, results=True):
       ...

Or collect futures all futures in batches that had arrived since the last iteration

    for batch in as_completed(futures, results=True).batches():
       for future in batch:
           ...

Additionally, for iterative algorithms you can add more futures into the `as_completed` iterator

    seq = as_completed(futures)

    for future in seq:
        y = future.result()
        if condition(y):
            new_future = client.submit(...)
            seq.add(new_future)  # add back into the loop

## Fire and Forget

`fire_and_forget`(obj) | Run tasks at least once, even if we release the futures

Sometimes we don’t care about gathering the result of a task, and only care about side effects that it might have, like writing a result to a file.

    >>> a = client.submit(load, filename)
    >>> b = client.submit(process, a)
    >>> c = client.submit(write, c, out_filename)

As noted above, Dask will stop work that doesn’t have any active futures. It thinks that because no one has a pointer to this data that no one cares. You can tell Dask to compute a task anyway, even if there are no active futures, using the `fire_and_forget` function:

    from dask.distributed import fire_and_forget

    >>> fire_and_forget(c)

This is particularly useful when a future may go out of scope, for example as part of a function:

    def process(filename):
        out_filename = 'out-' + filename
        a = client.submit(load, filename)
        b = client.submit(process, a)
        c = client.submit(write, c, out_filename)
        fire_and_forget(c)
        return  # here we lose the reference to c, but that's now ok

    for filename in filenames:
        process(filename)

## Submit Tasks from Tasks

`get_client`([address, timeout]) | Get a client while within a task
`secede`() | Have this task secede from the worker’s thread pool

Tasks can launch other tasks by getting their own client. This enables complex and highly dynamic workloads.

    from dask.distributed import get_client

    def my_function(x):
        ...

        # Get locally created client
        client = get_client()

        # Do normal client operations, asking cluster for computation
        a = client.submit(...)
        b = client.submit(...)
        a, b = client.gather([a, b])

        return a + b

It also allows you to set up long running tasks that watch other resources like sockets or physical sensors:

    def monitor(device):
       client = get_client()
       while True:
           data = device.read_data()
           future = client.submit(process, data)
           fire_and_forget(future)

    for device in devices:
        fire_and_forget(client.submit(monitor))

However, each running task takes up a single thread, and so if you launch many tasks that launch other tasks then it is possible to deadlock the system if you are not careful. You can call the `secede` function from within a task to have it remove itself from the dedicated thread pool into an administrative thread that does not take up a slot within the Dask worker:

    from dask.distributed import get_client, secede

    def monitor(device):
       client = get_client()
       secede()
       while True:
           data = device.read_data()
           future = client.submit(process, data)
           fire_and_forget(future)

## Coordinate Data Between Clients

`Queue`([name, client, maxsize]) | Distributed Queue
`Variable`([name, client, maxsize]) | Distributed Global Variable

In the section above we saw that you could have multiple clients running at the same time, each of which generated and manipulated futures. These clients can coordinate with each other using Dask `Queue` and `Variable` objects, which can communicate futures or small bits of data between clients sensibly.

Dask queues follow the API for the standard Python Queue, but now move futures or small messages between clients. Queues serialize sensibly and reconnect themselves on remote clients if necessary.

    from dask.distributed import Queue

    def load_and_submit(filename):
        data = load(filename)
        client = get_client()
        future = client.submit(process, data)
        queue.put(future)

    client = Client()

    queue = Queue()

    for filename in filenames:
        future = client.submit(load_and_submit, filename)
        fire_and_forget(filename)

    while True:
        future = queue.get()
        print(future.result())

Queues can also send small pieces of information, anything that is msgpack encodable (ints, strings, bools, lists, dicts, etc..). This can be useful to send back small scores or administrative messages:

    def func(x):
        try:
           ...
        except Exception as e:
            error_queue.put(str(e))

    error_queue = Queue()

Variables are like Queues in that they communicate futures and small data between clients. However variables hold only a single value. You can get or set that value at any time.

    >>> var = Variable('stopping-criterion')
    >>> var.set(False)

    >>> var.get()
    False

This is often used to signal stopping criteria or current parameters, etc. between clients.

If you want to share large pieces of information then scatter the data first

    >>> parameters = np.array(...)
    >>> future = client.scatter(parameters)
    >>> var.set(future)

## API

Client

`Client`([address, loop, timeout, ...]) | Connect to and drive computation on a distributed Dask cluster
`Client.cancel`(futures[, asynchronous, force]) | Cancel running futures
`Client.compute`(collections[, sync, ...]) | Compute dask collections on cluster
`Client.gather`(futures[, errors, maxsize, ...]) | Gather futures from distributed memory
`Client.get`(dsk, keys[, restrictions, ...]) | Compute dask graph
`Client.get_dataset`(name, \*\*kwargs) | Get named dataset from the scheduler
`Client.get_executor`(\*\*kwargs) | Return a concurrent.futures Executor for submitting tasks on this Client.
`Client.has_what`([workers]) | Which keys are held by which workers
`Client.list_datasets`(\*\*kwargs) | List named datasets available on the scheduler
`Client.map`(func, \*iterables, \*\*kwargs) | Map a function on a sequence of arguments
`Client.ncores`([workers]) | The number of threads/cores available on each worker node
`Client.persist`(collections[, ...]) | Persist dask collections on cluster
`Client.publish_dataset`(\*\*kwargs) | Publish named datasets to scheduler
`Client.rebalance`([futures, workers]) | Rebalance data within network
`Client.replicate`(futures[, n, workers, ...]) | Set replication of futures within network
`Client.restart`(\*\*kwargs) | Restart the distributed network
`Client.run`(function, \*args, \*\*kwargs) | Run a function on all workers outside of task scheduling system
`Client.run_on_scheduler`(function, \*args, ...) | Run a function on the scheduler process
`Client.scatter`(data[, workers, broadcast, ...]) | Scatter data into distributed memory
`Client.shutdown`([timeout]) | Close this client
`Client.scheduler_info`(\*\*kwargs) | Basic information about the workers in the cluster
`Client.shutdown`([timeout]) | Close this client
`Client.start_ipython_workers`([workers, ...]) | Start IPython kernels on workers
`Client.start_ipython_scheduler`([magic_name, ...]) | Start IPython kernel on the scheduler
`Client.submit`(func, \*args, \*\*kwargs) | Submit a function application to the scheduler
`Client.unpublish_dataset`(name, \*\*kwargs) | Remove named datasets from scheduler
`Client.upload_file`(filename, \*\*kwargs) | Upload local package to workers
`Client.who_has`([futures]) | The workers storing each future’s data

Future

`Future`(key, client[, inform, state]) | A remotely running computation
`Future.add_done_callback`(fn) | Call callback on future when callback has finished
`Future.cancel`([force]) | Cancel request to run this future
`Future.cancelled`() | Returns True if the future has been cancelled
`Future.done`() | Is the computation complete?
`Future.exception`([timeout]) | Return the exception of a failed task
`Future.result`([timeout]) | Wait until computation completes, gather result to local process.
`Future.traceback`([timeout]) | Return the traceback of a failed task

Functions

`as_completed`([futures, loop, with_results]) | Return futures in the order in which they complete
`fire_and_forget`(obj) | Run tasks at least once, even if we release the futures
`get_client`([address, timeout]) | Get a client while within a task
`secede`() | Have this task secede from the worker’s thread pool
`wait`(fs[, timeout, return_when]) | Wait until all futures are complete

`distributed.` `as_completed`(futures=None, loop=None, with_results=False)

  Return futures in the order in which they complete

  This returns an iterator that yields the input future objects in the order in which they complete. Calling `next` on the iterator will block until the next future completes, irrespective of order.

  Additionally, you can also add more futures to this object during computation with the `.add` method

  Examples

      >>> x, y, z = client.map(inc, [1, 2, 3])
      >>> for future in as_completed([x, y, z]):
      ...     print(future.result())
      3
      2
      4

  Add more futures during computation

      >>> x, y, z = client.map(inc, [1, 2, 3])
      >>> ac = as_completed([x, y, z])
      >>> for future in ac:
      ...     print(future.result())
      ...     if random.random() < 0.5:
      ...         ac.add(c.submit(double, future))
      4
      2
      8
      3
      6
      12
      24

  Optionally wait until the result has been gathered as well

      >>> ac = as_completed([x, y, z], with_results=True)
      >>> for future, result in ac:
      ...     print(result)
      2
      4
      3

`distributed.` `fire_and_forget`(obj)

  Run tasks at least once, even if we release the futures

  Under normal operation Dask will not run any tasks for which there is not an active future (this avoids unnecessary work in many situations). However sometimes you want to just fire off a task, not track its future, and expect it to finish eventually. You can use this function on a future or collection of futures to ask Dask to complete the task even if no active client is tracking it.

  The results will not be kept in memory after the task completes (unless there is an active future) so this is only useful for tasks that depend on side effects.

  Parameters: | obj (Future, list, dict, dask collection) – The futures that you want to run at least once

  Examples

      >>> fire_and_forget(client.submit(func, *args))

`distributed.` `get_client`(address=None, timeout=3)

  Get a client while within a task

  This client connects to the same scheduler to which the worker is connected

  Examples

      >>> def f():
      ...     client = get_client()
      ...     futures = client.map(lambda x: x + 1, range(10))  # spawn many tasks
      ...     results = client.gather(futures)
      ...     return sum(results)

      >>> future = client.submit(f)
      >>> future.result()
      55

  See also

  `get_worker()`, `worker_client()`, `secede()`

`distributed.` `secede`()

  Have this task secede from the worker’s thread pool

  This opens up a new scheduling slot and a new thread for a new task.

  Examples

      >>> def mytask(x):
      ...     # do some work
      ...     client = get_client()
      ...     futures = client.map(...)  # do some remote work
      ...     secede()  # while that work happens, remove ourself from the pool
      ...     return client.gather(futures)  # return gathered results

  See also

  `get_client()`, `get_worker()`

`distributed.` `wait`(fs, timeout=None, return_when='ALL_COMPLETED')

  Wait until all futures are complete

  Parameters: | fs (list of futures) – timeout (number, optional) – Time in seconds after which to raise a gen.TimeoutError
  Returns: |
  Return type: | Named tuple of completed, not completed

class `distributed.` `Client`(address=None, loop=None, timeout=5, set_as_default=True, scheduler_file=None, security=None, start=None, asynchronous=False, name=None, **kwargs)

  Connect to and drive computation on a distributed Dask cluster

  The Client connects users to a dask.distributed compute cluster. It provides an asynchronous user interface around functions and futures. This class resembles executors in `concurrent.futures` but also allows `Future` objects within `submit/map` calls.

  Parameters: | address (string, or Cluster) – This can be the address of a `Scheduler` server like a string `'127.0.0.1:8786'` or a cluster object like `LocalCluster()` timeout (int) – Timeout duration for initial connection to the scheduler set_as_default (bool (True)) – Claim this scheduler as the global dask scheduler scheduler_file (string (optional)) – Path to a file with scheduler information if available security ((optional)) – Optional security information asynchronous (bool (False by default)) – Set to True if this client will be used within a Tornado event loop name (string (optional)) – Gives the client a name that will be included in logs generated on the scheduler for matters relating to this client

  Examples

  Provide cluster’s scheduler node address on initialization:

      >>> client = Client('127.0.0.1:8786')

  Use `submit` method to send individual computations to the cluster

      >>> a = client.submit(add, 1, 2)
      >>> b = client.submit(add, 10, 20)

  Continue using submit or map on results to build up larger computations

      >>> c = client.submit(add, a, b)

  Gather results with the `gather` method.

      >>> client.gather(c)
      33

  See also

  `distributed.scheduler.Scheduler`
    Internal scheduler
  `call_stack`(futures=None)

    The actively running call stack of all relevant keys

    Parameters: | futures (list (optional)) – A list of futures, defaults to all data

    Examples

        >>> df = dd.read_parquet(...).persist()
        >>> client.call_stack(df)  # call on collections

        >>> client.call_stack()  # Or call with no arguments for all activity

  `cancel`(futures, asynchronous=None, force=False)

    Cancel running futures

    This stops future tasks from being scheduled if they have not yet run and deletes them if they have already run. After calling, this result and all dependent results will no longer be accessible

    Parameters: | futures (list of Futures) – force (boolean (False)) – Cancel this future even if other clients desire it

  `channel`(*args, **kwargs)

    Deprecated: see dask.distributed.Queue instead

  `close`(timeout=10)

    Close this client

    Clients will also close automatically when your Python session ends

    If you started a client without arguments like `Client()` then this will also close the local cluster that was started at the same time.

    See also

    `Client.restart()`

  `compute`(collections, sync=False, optimize_graph=True, workers=None, allow_other_workers=False, resources=None, **kwargs)

    Compute dask collections on cluster

    Parameters: | collections (iterable of dask objects or single dask object) – Collections like dask.array or dataframe or dask.value objects sync (bool (optional)) – Returns Futures if False (default) or concrete values if True optimize_graph (bool) – Whether or not to optimize the underlying graphs workers (str, list, dict) – Which workers can run which parts of the computation If a string a list then the output collections will run on the listed workers, but other sub-computations can run anywhere If a dict then keys should be (tuples of) collections and values should be addresses or lists. allow_other_workers (bool, list) – If True then all restrictions in workers= are considered loose If a list then only the keys for the listed collections are loose **kwargs – Options to pass to the graph optimize calls
    Returns: |
    Return type: | List of Futures if input is a sequence, or a single future otherwise

    Examples

        >>> from dask import delayed
        >>> from operator import add
        >>> x = delayed(add)(1, 2)
        >>> y = delayed(add)(x, x)
        >>> xx, yy = client.compute([x, y])
        >>> xx
        <Future: status: finished, key: add-8f6e709446674bad78ea8aeecfee188e>
        >>> xx.result()
        3
        >>> yy.result()
        6

    Also support single arguments

        >>> xx = client.compute(x)

    See also

    `Client.get()`
      Normal synchronous dask.get function
  `gather`(futures, errors='raise', maxsize=0, direct=None, asynchronous=None)

    Gather futures from distributed memory

    Accepts a future, nested container of futures, iterator, or queue. The return type will match the input type.

    Parameters: | futures (Collection of futures) – This can be a possibly nested collection of Future objects. Collections can be lists, sets, iterators, queues or dictionaries errors (string) – Either ‘raise’ or ‘skip’ if we should raise if a future has erred or skip its inclusion in the output collection maxsize (int) – If the input is a queue then this produces an output queue with a maximum size.
    Returns: | results (a collection of the same type as the input, but now with) gathered results rather than futures

    Examples

        >>> from operator import add
        >>> c = Client('127.0.0.1:8787')
        >>> x = c.submit(add, 1, 2)
        >>> c.gather(x)
        3
        >>> c.gather([x, [x], x])  # support lists and dicts
        [3, [3], 3]

        >>> seq = c.gather(iter([x, x]))  # support iterators
        >>> next(seq)
        3

    See also

    `Client.scatter()`
      Send data out to cluster
  `get`(dsk, keys, restrictions=None, loose_restrictions=None, resources=None, sync=True, asynchronous=None, **kwargs)

    Compute dask graph

    Parameters: | dsk (dict) – keys (object, or nested lists of objects) – restrictions (dict (optional)) – A mapping of {key: {set of worker hostnames}} that restricts where jobs can take place sync (bool (optional)) – Returns Futures if False or concrete values if True (default).

    Examples

        >>> from operator import add
        >>> c = Client('127.0.0.1:8787')
        >>> c.get({'x': (add, 1, 2)}, 'x')
        3

    See also

    `Client.compute()`
      Compute asynchronous collections
  `get_dataset`(name, **kwargs)

    Get named dataset from the scheduler

    See also

    `Client.publish_dataset()`, `Client.list_datasets()`

  `get_executor`(**kwargs)

    Return a concurrent.futures Executor for submitting tasks on this Client.

    Parameters: | **kwargs – Any submit()- or map()- compatible arguments, such as workers or resources.
    Returns: | An Executor object that’s fully compatible with the concurrent.futures API.

  static `get_restrictions`(collections, workers, allow_other_workers)

    Get restrictions from inputs to compute/persist

  `get_versions`(check=False)

    Return version info for the scheduler, all workers and myself

    Parameters: | check (boolean, default False) – raise ValueError if all required & optional packages do not match

    Examples

        >>> c.get_versions()

  `has_what`(workers=None, **kwargs)

    Which keys are held by which workers

    Parameters: | workers (list (optional)) – A list of worker addresses, defaults to all

    Examples

        >>> x, y, z = c.map(inc, [1, 2, 3])
        >>> wait([x, y, z])
        >>> c.has_what()
        {'192.168.1.141:46784': ['inc-1c8dd6be1c21646c71f76c16d09304ea',
                                 'inc-fd65c238a7ea60f6a01bf4c8a5fcf44b',
                                 'inc-1e297fc27658d7b67b3a758f16bcf47a']}

    See also

    `Client.who_has()`, `Client.ncores()`

  `list_datasets`(**kwargs)

    List named datasets available on the scheduler

    See also

    `Client.publish_dataset()`, `Client.get_dataset()`

  `map`(func, *iterables, **kwargs)

    Map a function on a sequence of arguments

    Arguments can be normal objects or Futures

    Parameters: | func (callable) – iterables (Iterables, Iterators, or Queues) – key (str, list) – Prefix for task names if string. Explicit names if list. pure (bool (defaults to True)) – Whether or not the function is pure. Set `pure=False` for impure functions like `np.random.random`. workers (set, iterable of sets) – A set of worker hostnames on which computations may be performed. Leave empty to default to all workers (common case)

    Examples

        >>> L = client.map(func, sequence)

    Returns: | List, iterator, or Queue of futures, depending on the type of the inputs.

    See also

    `Client.submit()`
      Submit a single function
  `nbytes`(keys=None, summary=True, **kwargs)

    The bytes taken up by each key on the cluster

    This is as measured by `sys.getsizeof` which may not accurately reflect the true cost.

    Parameters: | keys (list (optional)) – A list of keys, defaults to all keys summary (boolean, (optional)) – Summarize keys into key types

    Examples

        >>> x, y, z = c.map(inc, [1, 2, 3])
        >>> c.nbytes(summary=False)
        {'inc-1c8dd6be1c21646c71f76c16d09304ea': 28,
         'inc-1e297fc27658d7b67b3a758f16bcf47a': 28,
         'inc-fd65c238a7ea60f6a01bf4c8a5fcf44b': 28}

        >>> c.nbytes(summary=True)
        {'inc': 84}

    See also

    `Client.who_has()`

  `ncores`(workers=None, **kwargs)

    The number of threads/cores available on each worker node

    Parameters: | workers (list (optional)) – A list of workers that we care about specifically. Leave empty to receive information about all workers.

    Examples

        >>> c.ncores()
        {'192.168.1.141:46784': 8,
         '192.167.1.142:47548': 8,
         '192.167.1.143:47329': 8,
         '192.167.1.144:37297': 8}

    See also

    `Client.who_has()`, `Client.has_what()`

  `normalize_collection`(collection)

    Replace collection’s tasks by already existing futures if they exist

    This normalizes the tasks within a collections task graph against the known futures within the scheduler. It returns a copy of the collection with a task graph that includes the overlapping futures.

    Examples

        >>> len(x.dask)  # x is a dask collection with 100 tasks
        100
        >>> set(client.futures).intersection(x.dask)  # some overlap exists
        10

        >>> x = client.normalize_collection(x)
        >>> len(x.dask)  # smaller computational graph
        20

    See also

    `Client.persist()`
      trigger computation of collection’s tasks
  `persist`(collections, optimize_graph=True, workers=None, allow_other_workers=None, resources=None, **kwargs)

    Persist dask collections on cluster

    Starts computation of the collection on the cluster in the background. Provides a new dask collection that is semantically identical to the previous one, but now based off of futures currently in execution.

    Parameters: | collections (sequence or single dask object) – Collections like dask.array or dataframe or dask.value objects optimize_graph (bool) – Whether or not to optimize the underlying graphs workers (str, list, dict) – Which workers can run which parts of the computation If a string a list then the output collections will run on the listed workers, but other sub-computations can run anywhere If a dict then keys should be (tuples of) collections and values should be addresses or lists. allow_other_workers (bool, list) – If True then all restrictions in workers= are considered loose If a list then only the keys for the listed collections are loose kwargs – Options to pass to the graph optimize calls
    Returns: |
    Return type: | List of collections, or single collection, depending on type of input.

    Examples

        >>> xx = client.persist(x)
        >>> xx, yy = client.persist([x, y])

    See also

    `Client.compute()`

  `processing`(workers=None)

    The tasks currently running on each worker

    Parameters: | workers (list (optional)) – A list of worker addresses, defaults to all

    Examples

        >>> x, y, z = c.map(inc, [1, 2, 3])
        >>> c.processing()
        {'192.168.1.141:46784': ['inc-1c8dd6be1c21646c71f76c16d09304ea',
                                 'inc-fd65c238a7ea60f6a01bf4c8a5fcf44b',
                                 'inc-1e297fc27658d7b67b3a758f16bcf47a']}

    See also

    `Client.stacks()`, `Client.who_has()`, `Client.has_what()`, `Client.ncores()`

  `profile`(key=None, start=None, stop=None, workers=None, merge_workers=True)

    Collect statistical profiling information about recent work

    Parameters: | key (str) – Key prefix to select, this is typically a function name like ‘inc’ Leave as None to collect all data start (time) – stop (time) – workers (list) – List of workers to restrict profile information

    Examples

        >>> client.profile()  # call on collections

  `publish_dataset`(**kwargs)

    Publish named datasets to scheduler

    This stores a named reference to a dask collection or list of futures on the scheduler. These references are available to other Clients which can download the collection or futures with `get_dataset`.

    Datasets are not immediately computed. You may wish to call `Client.persist` prior to publishing a dataset.

    Parameters: | kwargs (dict) – named collections to publish on the scheduler

    Examples

    Publishing client:

        >>> df = dd.read_csv('s3://...')
        >>> df = c.persist(df)
        >>> c.publish_dataset(my_dataset=df)

    Receiving client:

        >>> c.list_datasets()
        ['my_dataset']
        >>> df2 = c.get_dataset('my_dataset')

    Returns: |
    Return type: | None

    See also

    `Client.list_datasets()`, `Client.get_dataset()`, `Client.unpublish_dataset()`, `Client.persist()`

  `rebalance`(futures=None, workers=None, **kwargs)

    Rebalance data within network

    Move data between workers to roughly balance memory burden. This either affects a subset of the keys/workers or the entire network, depending on keyword arguments.

    This operation is generally not well tested against normal operation of the scheduler. It it not recommended to use it while waiting on computations.

    Parameters: | futures (list, optional) – A list of futures to balance, defaults all data workers (list, optional) – A list of workers on which to balance, defaults to all workers

  `replicate`(futures, n=None, workers=None, branching_factor=2, **kwargs)

    Set replication of futures within network

    Copy data onto many workers. This helps to broadcast frequently accessed data and it helps to improve resilience.

    This performs a tree copy of the data throughout the network individually on each piece of data. This operation blocks until complete. It does not guarantee replication of data to future workers.

    Parameters: | futures (list of futures) – Futures we wish to replicate n (int, optional) – Number of processes on the cluster on which to replicate the data. Defaults to all. workers (list of worker addresses) – Workers on which we want to restrict the replication. Defaults to all. branching_factor (int, optional) – The number of workers that can copy data in each generation

    Examples

        >>> x = c.submit(func, *args)
        >>> c.replicate([x])  # send to all workers
        >>> c.replicate([x], n=3)  # send to three workers
        >>> c.replicate([x], workers=['alice', 'bob'])  # send to specific
        >>> c.replicate([x], n=1, workers=['alice', 'bob'])  # send to one of specific workers
        >>> c.replicate([x], n=1)  # reduce replications

    See also

    `Client.rebalance()`

  `restart`(**kwargs)

    Restart the distributed network

    This kills all active work, deletes all data on the network, and restarts the worker processes.

  `run`(function, *args, **kwargs)

    Run a function on all workers outside of task scheduling system

    This calls a function on all currently known workers immediately, blocks until those results come back, and returns the results asynchronously as a dictionary keyed by worker address. This method if generally used for side effects, such and collecting diagnostic information or installing libraries.

    If your function takes an input argument named `dask_worker` then that variable will be populated with the worker itself.

    Parameters: | function (callable) – *args (arguments for remote function) – **kwargs (keyword arguments for remote function) – workers (list) – Workers on which to run the function. Defaults to all known workers.

    Examples

        >>> c.run(os.getpid)
        {'192.168.0.100:9000': 1234,
         '192.168.0.101:9000': 4321,
         '192.168.0.102:9000': 5555}

    Restrict computation to particular workers with the `workers=` keyword argument.

        >>> c.run(os.getpid, workers=['192.168.0.100:9000',
        ...                           '192.168.0.101:9000'])
        {'192.168.0.100:9000': 1234,
         '192.168.0.101:9000': 4321}

        >>> def get_status(dask_worker):
        ...     return dask_worker.status

        >>> c.run(get_hostname)
        {'192.168.0.100:9000': 'running',
         '192.168.0.101:9000': 'running}

  `run_coroutine`(function, *args, **kwargs)

    Spawn a coroutine on all workers.

    This spaws a coroutine on all currently known workers and then waits for the coroutine on each worker. The coroutines’ results are returned as a dictionary keyed by worker address.

    Parameters: | function (a coroutine function) – (typically a function wrapped in gen.coroutine or a Python 3.5+ async function) *args (arguments for remote function) – **kwargs (keyword arguments for remote function) – wait (boolean (default True)) – Whether to wait for coroutines to end. workers (list) – Workers on which to run the function. Defaults to all known workers.

  `run_on_scheduler`(function, *args, **kwargs)

    Run a function on the scheduler process

    This is typically used for live debugging. The function should take a keyword argument `dask_scheduler=`, which will be given the scheduler object itself.

    Examples

        >>> def get_number_of_tasks(dask_scheduler=None):
        ...     return len(dask_scheduler.task_state)

        >>> client.run_on_scheduler(get_number_of_tasks)
        100

    See also

    `Client.run()`
      Run a function on all workers
    `Client.start_ipython_scheduler()`
      Start an IPython session on scheduler
  `scatter`(data, workers=None, broadcast=False, direct=None, hash=True, maxsize=0, timeout=3, asynchronous=None)

    Scatter data into distributed memory

    This moves data from the local client process into the workers of the distributed scheduler. Note that it is often better to submit jobs to your workers to have them load the data rather than loading data locally and then scattering it out to them.

    Parameters: | data (list, iterator, dict, Queue, or object) – Data to scatter out to workers. Output type matches input type. workers (list of tuples (optional)) – Optionally constrain locations of data. Specify workers as hostname/port pairs, e.g. `('127.0.0.1', 8787)`. broadcast (bool (defaults to False)) – Whether to send each data element to all workers. By default we round-robin based on number of cores. direct (bool (defaults to automatically check)) – Send data directly to workers, bypassing the central scheduler This avoids burdening the scheduler but assumes that the client is able to talk directly with the workers. maxsize (int (optional)) – Maximum size of queue if using queues, 0 implies infinite hash (bool (optional)) – Whether or not to hash data to determine key. If False then this uses a random key
    Returns: |
    Return type: | List, dict, iterator, or queue of futures matching the type of input.

    Examples

        >>> c = Client('127.0.0.1:8787')
        >>> c.scatter(1)
        <Future: status: finished, key: c0a8a20f903a4915b94db8de3ea63195>

        >>> c.scatter([1, 2, 3])
        [<Future: status: finished, key: c0a8a20f903a4915b94db8de3ea63195>,
         <Future: status: finished, key: 58e78e1b34eb49a68c65b54815d1b158>,
         <Future: status: finished, key: d3395e15f605bc35ab1bac6341a285e2>]

        >>> c.scatter({'x': 1, 'y': 2, 'z': 3})
        {'x': <Future: status: finished, key: x>,
         'y': <Future: status: finished, key: y>,
         'z': <Future: status: finished, key: z>}

    Constrain location of data to subset of workers

        >>> c.scatter([1, 2, 3], workers=[('hostname', 8788)])

    Handle streaming sequences of data with iterators or queues

        >>> seq = c.scatter(iter([1, 2, 3]))
        >>> next(seq)
        <Future: status: finished, key: c0a8a20f903a4915b94db8de3ea63195>,

    Broadcast data to all workers

        >>> [future] = c.scatter([element], broadcast=True)

    See also

    `Client.gather()`
      Gather data back to local process
  `scheduler_info`(**kwargs)

    Basic information about the workers in the cluster

    Examples

        >>> c.scheduler_info()
        {'id': '2de2b6da-69ee-11e6-ab6a-e82aea155996',
         'services': {},
         'type': 'Scheduler',
         'workers': {'127.0.0.1:40575': {'active': 0,
                                         'last-seen': 1472038237.4845693,
                                         'name': '127.0.0.1:40575',
                                         'services': {},
                                         'stored': 0,
                                         'time-delay': 0.0061032772064208984}}}

  `shutdown`(timeout=10)

    Close this client

    Clients will also close automatically when your Python session ends

    If you started a client without arguments like `Client()` then this will also close the local cluster that was started at the same time.

    See also

    `Client.restart()`

  `stacks`(workers=None)

    The task queues on each worker

    Parameters: | workers (list (optional)) – A list of worker addresses, defaults to all

    Examples

        >>> x, y, z = c.map(inc, [1, 2, 3])
        >>> c.stacks()
        {'192.168.1.141:46784': ['inc-1c8dd6be1c21646c71f76c16d09304ea',
                                 'inc-fd65c238a7ea60f6a01bf4c8a5fcf44b',
                                 'inc-1e297fc27658d7b67b3a758f16bcf47a']}

    See also

    `Client.processing()`, `Client.who_has()`, `Client.has_what()`, `Client.ncores()`

  `start`(**kwargs)

    Start scheduler running in separate thread

  `start_ipython_scheduler`(magic_name='scheduler_if_ipython', qtconsole=False, qtconsole_args=None)

    Start IPython kernel on the scheduler

    Parameters: | magic_name (str or None (optional)) – If defined, register IPython magic with this name for executing code on the scheduler. If not defined, register %scheduler magic if IPython is running. qtconsole (bool (optional)) – If True, launch a Jupyter QtConsole connected to the worker(s). qtconsole_args (list(str) (optional)) – Additional arguments to pass to the qtconsole on startup.

    Examples

        >>> c.start_ipython_scheduler()
        >>> %scheduler scheduler.processing
        {'127.0.0.1:3595': {'inc-1', 'inc-2'},
         '127.0.0.1:53589': {'inc-2', 'add-5'}}

        >>> c.start_ipython_scheduler(qtconsole=True)

    Returns: | connection_info – connection_info dict containing info necessary to connect Jupyter clients to the scheduler.
    Return type: | dict

    See also

    `Client.start_ipython_workers()`
      Start IPython on the workers
  `start_ipython_workers`(workers=None, magic_names=False, qtconsole=False, qtconsole_args=None)

    Start IPython kernels on workers

    Parameters: | workers (list (optional)) – A list of worker addresses, defaults to all magic_names (str or list(str) (optional)) – If defined, register IPython magics with these names for executing code on the workers. If string has asterix then expand asterix into 0, 1, ..., n for n workers qtconsole (bool (optional)) – If True, launch a Jupyter QtConsole connected to the worker(s). qtconsole_args (list(str) (optional)) – Additional arguments to pass to the qtconsole on startup.

    Examples

        >>> info = c.start_ipython_workers()
        >>> %remote info['192.168.1.101:5752'] worker.data
        {'x': 1, 'y': 100}

        >>> c.start_ipython_workers('192.168.1.101:5752', magic_names='w')
        >>> %w worker.data
        {'x': 1, 'y': 100}

        >>> c.start_ipython_workers('192.168.1.101:5752', qtconsole=True)

    Add asterix * in magic names to add one magic per worker

        >>> c.start_ipython_workers(magic_names='w_*')
        >>> %w_0 worker.data
        {'x': 1, 'y': 100}
        >>> %w_1 worker.data
        {'z': 5}

    Returns: | iter_connection_info – List of connection_info dicts containing info necessary to connect Jupyter clients to the workers.
    Return type: | list

    See also

    `Client.start_ipython_scheduler()`
      start ipython on the scheduler
  `submit`(func, *args, **kwargs)

    Submit a function application to the scheduler

    Parameters: | func (callable) – *args – **kwargs – pure (bool (defaults to True)) – Whether or not the function is pure. Set `pure=False` for impure functions like `np.random.random`. workers (set, iterable of sets) – A set of worker hostnames on which computations may be performed. Leave empty to default to all workers (common case) allow_other_workers (bool (defaults to False)) – Used with workers. Inidicates whether or not the computations may be performed on workers that are not in the workers set(s).

    Examples

        >>> c = client.submit(add, a, b)

    Returns: |
    Return type: | Future

    See also

    `Client.map()`
      Submit on many arguments at once
  `unpublish_dataset`(name, **kwargs)

    Remove named datasets from scheduler

    Examples

        >>> c.list_datasets()
        ['my_dataset']
        >>> c.unpublish_datasets('my_dataset')
        >>> c.list_datasets()
        []

    See also

    `Client.publish_dataset()`

  `upload_file`(filename, **kwargs)

    Upload local package to workers

    This sends a local file up to all worker nodes. This file is placed into a temporary directory on Python’s system path so any .py, .pyc, .egg or .zip files will be importable.

    Parameters: | filename (string) – Filename of .py, .pyc, .egg or .zip file to send to workers

    Examples

        >>> client.upload_file('mylibrary.egg')
        >>> from mylibrary import myfunc
        >>> L = c.map(myfunc, seq)

  `who_has`(futures=None, **kwargs)

    The workers storing each future’s data

    Parameters: | futures (list (optional)) – A list of futures, defaults to all data

    Examples

        >>> x, y, z = c.map(inc, [1, 2, 3])
        >>> wait([x, y, z])
        >>> c.who_has()
        {'inc-1c8dd6be1c21646c71f76c16d09304ea': ['192.168.1.141:46784'],
         'inc-1e297fc27658d7b67b3a758f16bcf47a': ['192.168.1.141:46784'],
         'inc-fd65c238a7ea60f6a01bf4c8a5fcf44b': ['192.168.1.141:46784']}

        >>> c.who_has([x, y])
        {'inc-1c8dd6be1c21646c71f76c16d09304ea': ['192.168.1.141:46784'],
         'inc-1e297fc27658d7b67b3a758f16bcf47a': ['192.168.1.141:46784']}

    See also

    `Client.has_what()`, `Client.ncores()`

  `asynchronous`

    Are we running in the event loop?

    This is true if the user signaled that we might be when creating the client as in the following:

        client = Client(asynchronous=True)

    However, we override this expectation if we can definitively tell that we are running from a thread that is not the event loop. This is common when calling get_client() from within a worker task. Even though the client was originally created in asynchronous mode we may find ourselves in contexts when it is better to operate synchronously.

class `distributed.` `Future`(key, client, inform=False, state=None)

  A remotely running computation

  A Future is a local proxy to a result running on a remote worker. A user manages future objects in the local Python process to determine what happens in the larger cluster.

  Examples

  Futures typically emerge from Client computations

      >>> my_future = client.submit(add, 1, 2)

  We can track the progress and results of a future

      >>> my_future
      <Future: status: finished, key: add-8f6e709446674bad78ea8aeecfee188e>

  We can get the result or the exception and traceback from the future

      >>> my_future.result()

  See also

  `Client`
    Creates futures
  `add_done_callback`(fn)

    Call callback on future when callback has finished

    The callback `fn` should take the future as its only argument. This will be called regardless of if the future completes successfully, errs, or is cancelled

    The callback is executed in a separate thread.

  `cancel`(force=False)

    Cancel request to run this future

    See also

    `Client.cancel()`

  `cancelled`()

    Returns True if the future has been cancelled

  `done`()

    Is the computation complete?

  `exception`(timeout=None, **kwargs)

    Return the exception of a failed task

    If timeout seconds are elapsed before returning, a TimeoutError is raised.

    See also

    `Future.traceback()`

  `result`(timeout=None)

    Wait until computation completes, gather result to local process.

    If timeout seconds are elapsed before returning, a TimeoutError is raised.

  `traceback`(timeout=None, **kwargs)

    Return the traceback of a failed task

    This returns a traceback object. You can inspect this object using the `traceback` module. Alternatively if you call `future.result()` this traceback will accompany the raised exception.

    If timeout seconds are elapsed before returning, a TimeoutError is raised.

    Examples

        >>> import traceback
        >>> tb = future.traceback()
        >>> traceback.export_tb(tb)
        [...]

    See also

    `Future.exception()`

class `distributed.` `Queue`(name=None, client=None, maxsize=0)

  Distributed Queue

  This allows multiple clients to share futures or small bits of data between each other with a multi-producer/multi-consumer queue. All metadata is sequentialized through the scheduler.

  Elements of the Queue must be either Futures or msgpack-encodable data (ints, strings, lists, dicts). All data is sent through the scheduler so it is wise not to send large objects. To share large objects scatter the data and share the future instead.

  Warning

  This object is experimental and has known issues in Python 2

  Examples

      >>> from dask.distributed import Client, Queue
      >>> client = Client()
      >>> queue = Queue('x')
      >>> future = client.submit(f, x)
      >>> queue.put(future)

  See also

  `Variable`
    shared variable between clients
  `get`(timeout=None, batch=False, **kwargs)

    Get data from the queue

    Parameters: | timeout (Number (optional)) – Time in seconds to wait before timing out batch (boolean, int (optional)) – If True then return all elements currently waiting in the queue. If an integer than return that many elements from the queue If False (default) then return one item at a time

  `put`(value, timeout=None, **kwargs)

    Put data into the queue

  `qsize`(**kwargs)

    Current number of elements in the queue

class `distributed.` `Variable`(name=None, client=None, maxsize=0)

  Distributed Global Variable

  This allows multiple clients to share futures and data between each other with a single mutable variable. All metadata is sequentialized through the scheduler. Race conditions can occur.

  Values must be either Futures or msgpack-encodable data (ints, lists, strings, etc..) All data will be kept and sent through the scheduler, so it is wise not to send too much. If you want to share a large amount of data then `scatter` it and share the future instead.

  Warning

  This object is experimental and has known issues in Python 2

  Examples

      >>> from dask.distributed import Client, Variable
      >>> client = Client()
      >>> x = Variable('x')
      >>> x.set(123)  # docttest: +SKIP
      >>> x.get()  # docttest: +SKIP
      123
      >>> future = client.submit(f, x)
      >>> x.set(future)

  See also

  `Queue`

  `delete`()

    Delete this variable

    Caution, this affects all clients currently pointing to this variable.

  `get`(timeout=None, **kwargs)

    Get the value of this variable

  `set`(value, **kwargs)

    Set the value of this variable

    Parameters: | value (Future or object) – Must be either a Future or a msgpack-encodable value