add lockmanager

assignment2/lockmanager.py

+from assignment2.paxos import Address
+from typing import Dict
+
+class LockManager:
+
+    def __init__(self) -> None:
+        self.locks: Dict[int, Address] = dict()
+
+    # returns true if lock is acquired or the same client tries to acquire 
+    # a locks it already has, false otherwise
+    def lock(self, value: int, client: Address) -> bool:
+        # acquire lock
+        if value not in self.locks:
+            self.locks[value] = client
+            return True
+
+        # client already acquired this lock before
+        if self.locks[value] == client:
+            return True
+        
+        # lock is not available
+        return False
+
+    # returns true if lock is unlocked, false otherwise
+    def unlock(self, value: int, client: Address) -> bool:
+        # lock does not exist
+        if value not in self.locks:
+            return False
+        
+        # client is not the owner of the locok
+        if self.locks[value] != client:
+            return False
+
+        # unlock
+        del self.locks[value]
+
+        return True
+
+
+# quick_test
+#if __name__ == "__main__":
+    #lm = LockManager()
+    #ca = ("hello", 1234)
+    #cb = ("hello", 5678)
+    #assert lm.lock(1, ca) == True
+    #assert lm.lock(2, cb) == True
+    #assert lm.lock(1, ca) == True
+    #assert lm.lock(1, cb) == False
+    #assert lm.unlock(1, cb) == False
+    #assert lm.unlock(1, ca) == True
+    #assert lm.unlock(2, cb) == True
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