I am preparing for an interview and would like to understand how to make a lock method thread-safe. I have basic knowledge of operating systems (OS) concepts, but I'm not well-versed in advanced topics. Therefore, I would appreciate a detailed explanation of the various approaches to achieving thread safety for the lock method.

Please provide multiple methods for making the lock method thread-safe.
Explain each method clearly and in-depth, especially if the concept is complex.
Provide code implementations for each approach, as I would like to avoid using any inbuilt threading libraries for the core logic. I will use threads only to create threads, but the rest of the logic should simulate locking mechanisms manually, similar to what would be expected in an interview.
After explaining each method, please compare the approaches at the end, highlighting the trade-offs and pros/cons of each.
I would like to cover as many categories of thread safety techniques as possible so that I can fully understand the topic and confidently discuss it during the interview."""
# Question 1: Locking the Tree of Space
# You have a world map represented as an M-Ary tree (sample tree below):

# You need to define three operations on it:
# lock(X, uid)
# unlock(X, uid)
# upgradeLock(X, uid)
# Where X is the name of a node in the tree (which is unique), and uid is the user performing the operation.
# Definitions for the Operations:
# Lock(X, uid):
# Lock takes exclusive access on the subtree rooted at X. Once lock(X, uid) succeeds:
# lock(A, anyUserId) should fail (returns false), where A is a descendant of X.
# lock(B, anyUserId) should fail (returns false), where X is a descendant of B.
# Lock operation cannot be performed on a node that is already locked, i.e., lock(X, anyUserId) should fail (returns false).
# Unlock(X, uid):
# Unlock reverts what was done by the lock operation. It can only be called on the same node on which user uid had called a lock before. Returns true if successful.
# UpgradeLock(X, uid):
# This helps the user uid upgrade their lock to an ancestor node. It is only possible if the node X already has locked descendants and all of them are locked by the same user uid. Upgrade should fail if there is any node which is a descendant of X that is locked by a different user. A successful upgrade will "lock" the node. UpgradeLock must not violate the consistency model required by Lock/Unlock.
# Notes:
# The number of nodes in the tree, N, is very large, so optimize the time complexity for the above algorithms.
# Input Format:
# The first line contains the number of nodes in the tree (N).
# The second line contains the number of children per node (m in an m-ary tree).
# The third line contains the number of queries (Q).
# Next N lines contain the NodeName (string) in the m-Ary Tree.
# The next Q lines contain queries in the format: OperationType NodeName UserId.
# Operation Type:
# 1 for Lock
# 2 for Unlock
# 3 for UpgradeLock
# NodeName: The name of any node (unique) in the m-Ary Tree.
# UserId: An integer representing a unique user.
# Example Input:
# 7
# 2
# 3
# World
# Asia
# Africa
# China
# India
# South Africa
# Egypt
# 1 China 9
# 2 India 9
# 3 Asia 9


# This input represents a 2-ary tree with 7 nodes as follows:
# World
# / <br/># Asia Africa
# / \ / <br/># China India South Africa Egypt


# Additional Notes:
# The tree is always fully balanced.
# Constraints:
# (1 < N < 5 \times 10^5)
# (1 < m < 30)
# (1 < Q < 5 \times 10^5)
# (1 < \text{length of NodeName} < 20)
# Optimize the time complexity:
# Lock: (O(\log_m N))
# Unlock: (O(\log_m N))
# UpgradeLock: (O(\text{numberOfLockedNodes} \times \log_m N))
# The lock operation on an already locked node should fail.
# Once UpgradeLock(X, uid) succeeds on X, it is equivalent to X being locked by uid. As per the definition, Lock(A/B, anyUser) should fail, and Unlock(X, uid) should also work.
# Upgrade lock operation on a node having no locked descendants should fail, and upgrade lock on an already locked node should also fail.


import sys


class Node:
def init(self, val):
self.val = val # Node value (name)
self.uid = None # User ID who locked the node
self.parent = None # Reference to parent node
self.children = [] # List of child nodes
self.isLocked = False # Lock status
self.lockedDescendantCount = 0 # Number of locked descendants


class Tree:
def init(self, n, m, node_list, queries):
self.node_list = []
self.node_map = {}

# Create node instances and map node names to instances
for name in node_list:
node = Node(name)
self.node_list.append(node)
self.node_map[name] = node

# Assign children to each node based on m-ary tree properties
for i in range(n):
for j in range(m):
child_index = m * i + j + 1
if child_index < n:
self.node_list[i].children.append(self.node_list[child_index])
self.node_list[child_index].parent = self.node_list[i]

self.root = self.node_list[0]

# Process queries
self.processed_queries = [query.strip().split() for query in queries]

def lock(self, node, uid):
# Check if node is already locked
if node.isLocked:
return False

# Check if any ancestors are locked
if self.isAncestorLocked(node):
return False

# Check if any descendants are locked
if node.lockedDescendantCount > 0:
return False

# Lock the node
node.isLocked = True
node.uid = uid

# Update ancestors' lockedDescendantCount
parent = node.parent
while parent:
parent.lockedDescendantCount += 1
parent = parent.parent

return True

def unlock(self, node, uid):
# Check if node is locked by uid
if not node.isLocked or node.uid != uid:
return False

# Unlock the node
node.isLocked = False
node.uid = None

# Update ancestors' lockedDescendantCount
parent = node.parent
while parent:
parent.lockedDescendantCount -= 1
parent = parent.parent

return True

def upgrade(self, node, uid):
# Check if node is already locked
if node.isLocked:
return False

# Check if any ancestors are locked
if self.isAncestorLocked(node):
return False

# Check if there are any locked descendants
if node.lockedDescendantCount == 0:
return False # No locked descendants to upgrade

# Collect all locked descendants
locked_descendants = []
if not self.collectLockedDescendants(node, uid, locked_descendants):
return False # Cannot upgrade due to locks by other users

# Unlock all locked descendants
for descendant in locked_descendants:
descendant.isLocked = False
descendant.uid = None
# Update ancestors' lockedDescendantCount
parent = descendant.parent
while parent:
parent.lockedDescendantCount -= 1
parent = parent.parent

# Lock the node
node.isLocked = True
node.uid = uid

# Update ancestors' lockedDescendantCount
parent = node.parent
while parent:
parent.lockedDescendantCount += 1
parent = parent.parent

return True

def isAncestorLocked(self, node):
# Traverse up to check if any ancestor is locked
current = node.parent
while current:
if current.isLocked:
return True
current = current.parent
return False

def collectLockedDescendants(self, node, uid, locked_nodes):
# If there are no locked descendants, return True
if node.lockedDescendantCount == 0:
return True

# Check if current node is locked
if node.isLocked:
if node.uid == uid:
locked_nodes.append(node)
else:
# Locked by a different user
return False

# Recurse into children only if necessary
for child in node.children:
if child.lockedDescendantCount > 0:
if not self.collectLockedDescendants(child, uid, locked_nodes):
return False
return True

def process_queries(self):
results = []
for query in self.processed_queries:
operation, node_name, uid = query
node = self.node_map[node_name]
if operation == "1":
result = self.lock(node, uid)
elif operation == "2":
result = self.unlock(node, uid)
elif operation == "3":
result = self.upgrade(node, uid)
else:
result = False # Invalid operation
results.append('true' if result else 'false')
return results


def main():
n = int(sys.stdin.readline())
m = int(sys.stdin.readline())
q = int(sys.stdin.readline())

node_list = []
for _ in range(n):
node_list.append(sys.stdin.readline().strip())

queries = []
for _ in range(q):
queries.append(sys.stdin.readline().strip())

tree = Tree(n, m, node_list, queries)
results = tree.process_queries()
for res in results:
print(res)

main()

"""