Future shock

What this concurrency question tests

This is an easy concurrency question in Python that probes your understanding of how threads and shared state interact. The question asks you to trace through a code snippet and predict its output — a straightforward way to test whether you understand the semantics of concurrent execution and potential race conditions.

To answer correctly, you need to reason about the order in which operations execute across multiple threads, how Python's Global Interpreter Lock (GIL) affects scheduling, and what state is visible to each thread at each step. Even on easy difficulty, the question rewards careful attention to detail and a clear mental model of thread interleaving rather than guessing.

• Thread scheduling and execution order
• Shared mutable state in concurrent programs
• Python's GIL and its implications for thread safety
• Visibility and atomicity of operations