Package duplicity :: Module dup_threading :: Class Value

Class Value


A thread-safe container of a reference to an object (but not the
object itself).

In particular this means it is safe to:

  value.set(1)

But unsafe to:

  value.get()['key'] = value

Where the latter must be done using something like:

  def _setprop():
    value.get()['key'] = value

  with_lock(value, _setprop)

Operations such as increments are best done as:

  value.transform(lambda val: val + 1)

Instance Methods

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__init__(self, value=None)
Initialuze with the given value.

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get(self)
Returns the value protected by this Value.

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set(self, value)
Resets the value protected by this Value.

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transform(self, fn)
Call fn with the current value as the parameter, and reset the value to the return value of fn.

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acquire(self)
Acquire this Value for mutually exclusive access.

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release(self)
Release this Value for mutually exclusive access.

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Method Details

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transform(self, fn)

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Call fn with the current value as the parameter, and reset the value to the return value of fn.

During the execution of fn, all other access to this Value is prevented.

If fn raised an exception, the value is not reset.

Returns the value returned by fn, or raises the exception raised by fn.

acquire(self)

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Acquire this Value for mutually exclusive access. Only ever needed when calling code must perform operations that cannot be done with get(), set() or transform().