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Bankers

Bankers - This is an implementation of the banker's deadlock algorithm

http://en.wikipedia.org/wiki/Banker%27s_algorithm

Usage

To find out, if a deadlock occurs you need to setup the following:

  1. You need a resource_vector, which is a list with the total amount of the different resources: e.g. 3 times Resource 1, 4 times Resource 2, 2 times Resource 3 => resource_vector = [3, 4, 2]

  2. You need a "need vector", which gets stored in the deadlock's requirements list. e.g. self.deadlock.requirements = [[0, 8, 3], [0, 2, 4]]. This would mean process 1 wants to have 0 instances of resource 1, 8 instances of resource 2 and 3 instances of resource 3, while process 2 wants 0 instances of resource 1, 2 instances of resource 2 and 4 instances of resource 4.

  3. You also need an initial occupancy list, which represents which resources have been occupied by which process. e.g. occupancies = [[0, 1, 0, 1], [0, 1, 0, 0]]. This would mean process 1 holds 0 instances of resource 1, 1 instance of resource 2 and so on.

  4. To calculate the resource_rest_vector (which represents the remaining resources available) you call set_resource_rest_vector with a resource_vector. The resource_rest_vector then gets calculated depending on the previously set occupancies and the given resource_vector.

The resource_vector is not stored in a class-field, since it is no longer needed after the calculation of the resource_rest_vector. The occupancies- and requirements-list however are needed in each step of the algorithm and this is why they get stored as fields.

Example

tests/test_examples.py

#-*- encoding: utf-8 -*-

from bankers.deadlock import Deadlock


def deadlock():
    resource_vector = [1, 2, 1, 3]
    d = Deadlock()
    d.requirements = [[1, 0, 0, 0], [0, 0, 1, 0], [1, 2, 1, 3]]
    d.occupancies = [[0, 1, 0, 0], [1, 1, 0, 0], [0, 0, 1, 0]]
    d.set_resource_rest_vector(resource_vector)
    print("Deadlock in first dataset? {0}".format(d.find_deadlock()))

def no_deadlock():
    resource_vector = [2, 2]
    d = Deadlock()
    d.occupancies = [[0, 1], [1, 0], [1, 0], [0, 1]]
    d.requirements = [[1, 0], [0, 0], [0, 1], [0, 0]]
    d.set_resource_rest_vector(resource_vector)
    print("Deadlock in first dataset? {0}".format(d.find_deadlock()))

def main():
    deadlock()
    no_deadlock()

if __name__ == '__main__':
    main()
Output:

Deadlock in first dataset? True
Deadlock in first dataset? False