Thread-safe task queue on a linked list

A task queue was written for one thread: a singly linked list with head and tail, where put appends at the tail and get removes from the head. Explain what goes wrong when many producer and consumer threads share it, then make it safe:

• put(value, timeout=None) blocks while the queue is at capacity (if one is set) and raises Full on timeout.
• get(timeout=None) blocks while the queue is empty and raises Empty on timeout.
• close() makes later put calls raise Closed; consumers drain what is left, then get raises Closed. Waiting threads must wake up.
• Every task is delivered exactly once; one producer's tasks come out in the order it put them.

class Empty(Exception): ...
class Full(Exception): ...
class Closed(Exception): ...


class TaskQueue:
    def __init__(self, capacity=None): ...
    def put(self, value, timeout=None): ...
    def get(self, timeout=None): ...
    def close(self): ...
    def __len__(self): ...