https://phosphorbbs.net/tags/thread-safety/ Recent content in Thread Safety on Phosphor BBS Hugo en-us Wed, 23 Sep 2026 00:00:00 +0000 https://phosphorbbs.net/blog/the-case-of-the-blended-batches/ Wed, 23 Sep 2026 00:00:00 +0000 https://phosphorbbs.net/blog/the-case-of-the-blended-batches/ <p>The jterm thread-safety suite exists to answer one question: <em>can a widget survive being redrawn from one thread while another mutates it?</em> It has run thousands of times across dozens of widgets, mostly to say yes. On the morning we cut the 0.1.1 release, it said no — and the test that failed wasn&rsquo;t even the one that was broken.</p> <h2 id="two-failures-two-days-apart">Two failures, two days apart</h2> <p>The release gate runs the whole suite, 2,926 tests. The first full run failed one test: <code>FireworksTest.renderFrameProducesOutput</code> — the fireworks animation was supposed to paint visible pixels after five frames and, once out of 2,926, it painted nothing. We re-ran the class in isolation: 12/12 green. Read the render path: fresh instance, deterministic math, five calls that each draw a rocket or particles. The failure looked like noise under load — the kind of flake you shrug at and re-run.</p>