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task.py
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task.py
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# -*- coding: utf-8 -*-
# Copyright (C) 2008-2013, Luis Pedro Coelho <luis@luispedro.org>
# vim: set ts=4 sts=4 sw=4 expandtab smartindent:
# LICENSE: MIT
'''
Task: contains the Task class.
This is the main class for using jug.
There are two main alternatives:
- Use the ``Task`` class directly to build up tasks, such as ``Task(function, arg0, ...)``.
- Rely on the ``TaskGenerator`` decorator as a shortcut for this.
'''
from .hash import new_hash_object, hash_update, hash_one
__all__ = [
'Task',
'Tasklet',
'recursive_dependencies',
'TaskGenerator',
'iteratetask',
'value',
]
alltasks = []
class _getitem(object):
def __init__(self, slice):
self.slice = slice
def __call__(self, obj):
obj = value(obj)
slice = value(self.slice)
return obj[slice]
def __jug_hash__(self):
return hash_one(('jug.task._getitem', self.slice))
def __repr__(self):
return 'jug.task._getitem(%s)' % self.slice
def __str__(self):
return 'jug.task._getitem(%s)' % self.slice
class TaskletMixin(object):
def __getitem__(self, slice):
return Tasklet(self, _getitem(slice))
class Task(TaskletMixin):
'''
T = Task(f, dep0, dep1,..., kw_arg0=kw_val0, kw_arg1=kw_val1, ...)
Defines a task, which is roughly equivalent to::
f(dep0, dep1,..., kw_arg0=kw_val0, kw_arg1=kw_val1, ...)
'''
store = None
# __slots__ = ('name', 'f', 'args', 'kwargs', '_hash','_lock')
def __init__(self, f, *args, **kwargs):
if getattr(f, 'func_name', '') == '<lambda>':
raise ValueError('''jug.Task does not work with lambda functions!
Write an email to the authors if you feel you have a strong reason to use them (they are a bit
tricky to support since the general code relies on the function name)''')
self.name = '%s.%s' % (f.__module__, f.__name__)
self.f = f
self.args = args
self.kwargs = kwargs
alltasks.append(self)
def run(self, force=False, save=True, debug_mode=False):
'''
task.run(force=False, save=True)
Performs the task.
Parameters
----------
force : boolean, optional
if true, always run the task (even if it ran before)
(default: False)
save : boolean, optional
if true, save the result to the store
(default: True)
'''
assert self.can_run()
if debug_mode: self._check_hash()
self._result = self._execute()
if save:
name = self.hash()
self.store.dump(self._result, name)
if debug_mode: self._check_hash()
return self._result
def _execute(self):
args = [value(dep) for dep in self.args]
kwargs = dict((key,value(dep)) for key,dep in self.kwargs.items())
return self.f(*args,**kwargs)
def _get_result(self):
if not hasattr(self, '_result'): self.load()
return self._result
result = property(_get_result, doc='Result value')
def value(self):
return self.result
def can_run(self):
'''
bool = task.can_run()
Returns true if all the dependencies have their results available.
'''
for dep in self.dependencies():
if not hasattr(dep, '_result') and not dep.can_load():
return False
return True
def is_loaded(self):
'''
loaded = task.is_loaded()
Returns True if the task is already loaded
'''
return hasattr(self, '_result')
def load(self):
'''
t.load()
Loads the results from the storage backend.
This function *always* loads from the backend even if the task is
already loaded. You can use `is_loaded` as a check if you want to avoid
this behaviour.
Returns
-------
Nothing
'''
assert self.can_load()
self._result = self.store.load(self.hash())
def invalidate(self):
'''
t.invalidate()
Equivalent to ``t.store.remove(t.hash())``. Useful for interactive use
(i.e., in ``jug shell`` mode).
'''
self.store.remove(self.hash())
def unload(self):
'''
t.unload()
Unload results (can be useful for saving memory).
'''
if hasattr(self, '_result'):
del self._result
def unload_recursive(self):
'''
t.unload_recursive()
Equivalent to::
for tt in recursive_dependencies(t): tt.unload()
'''
def checked_unload_recursive(t, visited):
if id(t) not in visited:
visited.add(id(t))
t.unload()
for dep in t.dependencies():
checked_unload_recursive(dep, visited)
checked_unload_recursive(self, set())
def dependencies(self):
'''
for dep in task.dependencies():
...
Iterates over all the first-level dependencies of task `t`
Parameters
----------
self : Task
Returns
-------
deps : generator
A generator over all of `self`'s dependencies
See Also
--------
recursive_dependencies : retrieve dependencies recursively
'''
queue = [self.args, self.kwargs.values()]
while queue:
deps = queue.pop()
for dep in deps:
if isinstance(dep, (Task, Tasklet)):
yield dep
elif isinstance(dep, (list, tuple)):
queue.append(dep)
elif isinstance(dep, dict):
queue.append(iter(dep.values()))
def can_load(self, store=None):
'''
bool = task.can_load()
Returns whether result is available.
'''
if store is None:
store = self.store
return store.can_load(self.hash())
def hash(self):
'''
fname = t.hash()
Returns the hash for this task.
The results are cached, so the first call can be much slower than
subsequent calls.
'''
return self.__jug_hash__()
def _compute_set_hash(self):
M = new_hash_object()
M.update(self.name.encode('utf-8'))
hash_update(M, enumerate(self.args))
hash_update(M, iter(self.kwargs.items()))
value = M.hexdigest().encode('utf-8')
self.__jug_hash__ = lambda : value
return value
def _check_hash(self):
if self.hash() != self._compute_set_hash():
hash_error_msg = ('jug error: Hash value of task (name: %s) changed unexpectedly.\n' % self.name)
hash_error_msg += 'Typical cause is that a Task function changed the value of an argument (which messes up downstream computations).'
raise RuntimeError(hash_error_msg)
def __jug_hash__(self):
return self._compute_set_hash()
def __str__(self):
'''String representation'''
return 'Task: %s()' % self.name
def __repr__(self):
'''Detailed representation'''
return 'Task(%s, args=%s, kwargs=%s)' % (self.name, self.args, self.kwargs)
def lock(self):
'''
locked = task.lock()
Tries to lock the task for the current process.
Returns True if the lock was acquired. The correct usage pattern is::
locked = task.lock()
if locked:
task.run()
else:
# someone else is already running this task!
Not that using can_lock() can lead to race conditions. The above
is the only fully correct method.
Returns
-------
locked : boolean
Whether the lock was obtained.
'''
if not hasattr(self, '_lock'):
self._lock = self.store.getlock(self.hash())
return self._lock.get()
def unlock(self):
'''
task.unlock()
Releases the lock.
If the lock was not held, this may remove another thread's lock!
'''
self._lock.release()
def is_locked(self):
'''
is_locked = t.is_locked()
Note that only calling lock() and checking the result atomically checks
for the lock(). This function can be much faster, though, and, therefore
is sometimes useful.
Returns
-------
is_locked : boolean
Whether the task **appears** to be locked.
See Also
--------
lock : create lock
unlock : destroy lock
'''
if not hasattr(self, '_lock'):
self._lock = self.store.getlock(self.hash())
return self._lock.is_locked()
class Tasklet(TaskletMixin):
'''
Tasklet
A Tasklet is a light-weight Task.
It looks like a Task, behaves like a Task, but its results are not saved in
the backend.
It is useful for very simple functions and is automatically generated on
subscripting a Task object::
t = Task(f, 1)
tlet = t[0]
``tlet`` will be a ``Tasklet``
See Also
--------
Task
'''
def __init__(self, base, f):
'''
Tasklet equivalent to::
f(value(base))
'''
self.base = base
self.f = f
self.unload = self.base.unload
self.unload_recursive = self.base.unload_recursive
def dependencies(self):
yield self.base
def value(self):
return self.f(value(self.base))
def can_load(self):
return self.base.can_load()
def _base_hash(self):
if isinstance(self.base, Tasklet):
return self.base._base_hash()
return self.base.hash()
def __jug_hash__(self):
import six
M = new_hash_object()
M.update(six.b('Tasklet'))
hash_update(M, [
('base', self.base),
('f', self.f),
])
return M.hexdigest().encode('utf-8')
def topological_sort(tasks):
'''
topological_sort(tasks)
Sorts a list of tasks topologically in-place. The list is sorted when
there is never a dependency between tasks[i] and tasks[j] if i < j.
'''
sorted = []
whites = set(tasks)
def dfs(t):
for dep in t.dependencies():
if dep in whites:
whites.remove(dep)
dfs(dep)
sorted.append(t)
while whites:
next = whites.pop()
dfs(next)
tasks[:] = sorted
def recursive_dependencies(t, max_level=-1):
'''
for dep in recursive_dependencies(t, max_level=-1):
...
Returns a generator that lists all recursive dependencies of task
Parameters
----------
t : Task
input task
max_level : integer, optional
Maximum recursion depth. Set to -1 or None for no recursion limit.
Returns
-------
deps : generator
A generator over all dependencies
'''
if max_level is None:
max_level = -1
if max_level == 0:
return
for dep in t.dependencies():
yield dep
for d2 in recursive_dependencies(dep, max_level - 1):
yield d2
def value(elem):
'''
value = value(obj)
Loads a task object recursively. This correcly handles lists,
dictonaries and eny other type handled by the tasks themselves.
Parameters
----------
obj : object
Anything that can be pickled or a Task
Returns
-------
value : object
The result of the task ``obj``
'''
if isinstance(elem, (Task, Tasklet)):
return elem.value()
elif type(elem) == list:
return [value(e) for e in elem]
elif type(elem) == tuple:
return tuple([value(e) for e in elem])
elif type(elem) == dict:
return dict((x,value(y)) for x,y in elem.items())
elif hasattr(elem, '__jug_value__'):
return elem.__jug_value__()
else:
return elem
def CachedFunction(f,*args,**kwargs):
'''
value = CachedFunction(f, *args, **kwargs)
is equivalent to::
task = Task(f, *args, **kwargs)
if not task.can_load():
task.run()
value = task.value()
That is, it calls the function if the value is available,
but caches the result for the future.
Parameters
----------
f : function
Any function except unnamed (lambda) functions
Returns
-------
value : result
Result of calling ``f(*args,**kwargs)``
See Also
--------
bvalue : function
An alternative way to achieve similar results to ``CachedFunction(f)``
using ``bvalue`` is::
ft = Task(f)
fvalue = bvalue(ft)
The alternative method is more flexible, but will only be execute
lazily. In particular, a ``jug status`` will not see past the
``bvalue`` call until ``jug execute`` is called to execute ``f``, while
a ``CachedFunction`` object will always execute.
'''
t = Task(f,*args, **kwargs)
if not t.can_load():
if not t.can_run():
raise ValueError('jug.CachedFunction: unable to run task %s' % t)
t.run()
return value(t)
class TaskGenerator(object):
'''
@TaskGenerator
def f(arg0, arg1, ...)
...
Turns f from a function into a task generator.
This means that calling ``f(arg0, arg1)`` results in:
``Task(f, arg0, arg1)``
'''
_jug_is_task_generator = True
def __init__(self, f):
self.f = f
def __getstate__(self):
from sys import modules
modname = getattr(self.f, '__module__', None)
fname = self.f.__name__
obj = getattr(modules[modname], fname, None)
if modname is None or (obj is not self and obj is not self.f):
raise RuntimeError('jug.TaskGenerator could not pickle function.\nA function must be defined at the top-module level')
return modname,fname
def __setstate__(self, state):
from sys import modules
modname,fname = state
self.f = getattr(modules[modname], fname)
def __call__(self, *args, **kwargs):
return Task(self.f, *args, **kwargs)
# This is lower case to be used like a function
class iteratetask(object):
'''
for a in iteratetask(task, n):
...
This creates an iterator that over the sequence ``task[0], task[1], ...,
task[n-1]``.
Parameters
----------
task : Task(let)
n : integer
Returns
-------
iterator
Bugs
----
There is no error checking that you have not missed elements at the end!
'''
def __init__(self, base, n):
self.base = base
self.n = n
def __getitem__(self, i):
if i >= self.n: raise IndexError
return self.base[i]
def __len__(self):
return self.n
def describe(t):
'''
description = describe(t)
Return a recursive description of the computation.
Parameters
----------
t : object
Returns
-------
description : obj
'''
if isinstance(t, Task):
description = { 'name': t.name, }
if len(t.args):
description['args'] = [describe(a) for a in t.args]
if len(t.kwargs):
description['kwargs'] = dict([(k,describe(v)) for k,v in t.kwargs.iteritems()])
meta = t.store.metadata(t)
if meta is not None:
description['meta'] = meta
return description
elif isinstance(t, Tasklet):
return {
'name': 'tasklet',
'operation': repr(t.f),
'base': describe(t.base)
}
elif isinstance(t, list):
return [describe(ti) for ti in t]
elif isinstance(t, dict):
return dict([(k,describe(v)) for k,v in t.items()])
elif isinstance(t, tuple):
return tuple(list(t))
return t