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