diff --git a/other/dijkstra_bankers_algorithm.py b/other/dijkstra_bankers_algorithm.py new file mode 100644 index 000000000..1f78941d3 --- /dev/null +++ b/other/dijkstra_bankers_algorithm.py @@ -0,0 +1,222 @@ +# A Python implementation of the Banker's Algorithm in Operating Systems using +# Processes and Resources +# { +# "Author: "Biney Kingsley (bluedistro@github.io), bineykingsley36@gmail.com", +# "Date": 28-10-2018 +# } +""" +The Banker's algorithm is a resource allocation and deadlock avoidance algorithm +developed by Edsger Dijkstra that tests for safety by simulating the allocation of +predetermined maximum possible amounts of all resources, and then makes a "s-state" +check to test for possible deadlock conditions for all other pending activities, +before deciding whether allocation should be allowed to continue. +[Source] Wikipedia +[Credit] Rosetta Code C implementation helped very much. + (https://rosettacode.org/wiki/Banker%27s_algorithm) +""" + +import time +from typing import Dict, List + +import numpy as np + +test_claim_vector = [8, 5, 9, 7] +test_allocated_res_table = [ + [2, 0, 1, 1], + [0, 1, 2, 1], + [4, 0, 0, 3], + [0, 2, 1, 0], + [1, 0, 3, 0], +] +test_maximum_claim_table = [ + [3, 2, 1, 4], + [0, 2, 5, 2], + [5, 1, 0, 5], + [1, 5, 3, 0], + [3, 0, 3, 3], +] + + +class BankersAlgorithm: + def __init__( + self, + claim_vector: List[int], + allocated_resources_table: List[List[int]], + maximum_claim_table: List[List[int]], + ) -> None: + """ + :param claim_vector: A nxn/nxm list depicting the amount of each resources + (eg. memory, interface, semaphores, etc.) available. + :param allocated_resources_table: A nxn/nxm list depicting the amount of each + resource each process is currently holding + :param maximum_claim_table: A nxn/nxm list depicting how much of each resource + the system currently has available + """ + self.__claim_vector = claim_vector + self.__allocated_resources_table = allocated_resources_table + self.__maximum_claim_table = maximum_claim_table + + def __processes_resource_summation(self) -> List[int]: + """ + Check for allocated resources in line with each resource in the claim vector + """ + return [ + sum(p_item[i] for p_item in self.__allocated_resources_table) + for i in range(len(self.__allocated_resources_table[0])) + ] + + def __available_resources(self) -> List[int]: + """ + Check for available resources in line with each resource in the claim vector + """ + return np.array(self.__claim_vector) - np.array( + self.__processes_resource_summation() + ) + + def __need(self) -> List[List[int]]: + """ + Implement safety checker that calculates the needs by ensuring that + max_claim[i][j] - alloc_table[i][j] <= avail[j] + """ + return [ + list(np.array(self.__maximum_claim_table[i]) - np.array(allocated_resource)) + for i, allocated_resource in enumerate(self.__allocated_resources_table) + ] + + def __need_index_manager(self) -> Dict[int, List[int]]: + """ + This function builds an index control dictionary to track original ids/indices + of processes when altered during execution of method "main" + Return: {0: [a: int, b: int], 1: [c: int, d: int]} + >>> BankersAlgorithm(test_claim_vector, test_allocated_res_table, + ... test_maximum_claim_table)._BankersAlgorithm__need_index_manager() + {0: [1, 2, 0, 3], 1: [0, 1, 3, 1], 2: [1, 1, 0, 2], 3: [1, 3, 2, 0], 4: [2, 0, 0, 3]} + """ + return {self.__need().index(i): i for i in self.__need()} + + def main(self, **kwargs) -> None: + """ + Utilize various methods in this class to simulate the Banker's algorithm + Return: None + >>> BankersAlgorithm(test_claim_vector, test_allocated_res_table, + ... test_maximum_claim_table).main(describe=True) + Allocated Resource Table + P1 2 0 1 1 + + P2 0 1 2 1 + + P3 4 0 0 3 + + P4 0 2 1 0 + + P5 1 0 3 0 + + System Resource Table + P1 3 2 1 4 + + P2 0 2 5 2 + + P3 5 1 0 5 + + P4 1 5 3 0 + + P5 3 0 3 3 + + Current Usage by Active Processes: 8 5 9 7 + Initial Available Resources: 1 2 2 2 + __________________________________________________ + + Process 3 is executing. + Updated available resource stack for processes: 5 2 2 5 + The process is in a safe state. + + Process 1 is executing. + Updated available resource stack for processes: 7 2 3 6 + The process is in a safe state. + + Process 2 is executing. + Updated available resource stack for processes: 7 3 5 7 + The process is in a safe state. + + Process 4 is executing. + Updated available resource stack for processes: 7 5 6 7 + The process is in a safe state. + + Process 5 is executing. + Updated available resource stack for processes: 8 5 9 7 + The process is in a safe state. + + """ + need_list = self.__need() + alloc_resources_table = self.__allocated_resources_table + available_resources = self.__available_resources() + need_index_manager = self.__need_index_manager() + for kw, val in kwargs.items(): + if kw and val is True: + self.__pretty_data() + print("_" * 50 + "\n") + while need_list: + safe = False + for each_need in need_list: + execution = True + for index, need in enumerate(each_need): + if need > available_resources[index]: + execution = False + break + if execution: + safe = True + # get the original index of the process from ind_ctrl db + for original_need_index, need_clone in need_index_manager.items(): + if each_need == need_clone: + process_number = original_need_index + print(f"Process {process_number + 1} is executing.") + # remove the process run from stack + need_list.remove(each_need) + # update available/freed resources stack + available_resources = np.array(available_resources) + np.array( + alloc_resources_table[process_number] + ) + print( + "Updated available resource stack for processes: " + + " ".join([str(x) for x in available_resources]) + ) + break + if safe: + print("The process is in a safe state.\n") + else: + print("System in unsafe state. Aborting...\n") + break + + def __pretty_data(self): + """ + Properly align display of the algorithm's solution + """ + print(" " * 9 + "Allocated Resource Table") + for item in self.__allocated_resources_table: + print( + f"P{self.__allocated_resources_table.index(item) + 1}" + + " ".join(f"{it:>8}" for it in item) + + "\n" + ) + print(" " * 9 + "System Resource Table") + for item in self.__maximum_claim_table: + print( + f"P{self.__maximum_claim_table.index(item) + 1}" + + " ".join(f"{it:>8}" for it in item) + + "\n" + ) + print( + "Current Usage by Active Processes: " + + " ".join(str(x) for x in self.__claim_vector) + ) + print( + "Initial Available Resources: " + + " ".join(str(x) for x in self.__available_resources()) + ) + time.sleep(1) + + +if __name__ == "__main__": + import doctest + + doctest.testmod()