← InterviewIntermediate
What Does the GIL Actually Prevent?
What is the GIL, and what does it mean for concurrency in Python?
The scenario
A CPython 3.12 service runs 16 threads. Half of each request is a database query, half is a pure-Python scoring loop. Throughput is the same at 16 threads as at 4, and the box has 16 cores at 30% utilization.
What it tests
- Whether the candidate states accurately what is serialized and what is not
- Whether they know threads still help for I/O-bound work
- Whether they know the answer is CPython-specific and version-dependent
Answer it out loud first. Recognising a good answer is not the same skill as producing one.