fix §7 TinyProfiler capture — run solve in subprocess#253
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jameslehoux merged 1 commit intomasterfrom Apr 19, 2026
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The original implementation tried to close the in-kernel Session, run a new one, redirect sys.stdout to capture TinyProfiler, and restart the Session. Two problems: 1. TinyProfiler prints via C++ streams on AMReX finalize. Python's `sys.stdout = captured` only redirects the Python-level stream, so TinyProfiler output went to the real terminal and was lost. 2. Tearing down + rebuilding AMReX inside a live kernel is fragile — HYPRE/AMReX static state can leave the second init in a bad shape. This manifested in Colab as a silent cell crash. Fix: run one profiled solve in a short-lived subprocess. Python's `capture_output=True` grabs fd 1 + fd 2 at the OS level, which captures everything TinyProfiler emits. The in-kernel Session is never touched, and the result dict is passed back via a `__RESULT__` JSON line. Also: expand the §7 markdown to explain the subprocess rationale and set expectations that TinyProfiler will break down the HYPRE solve (which §3 already showed is 96%+ of wall time).
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The original implementation tried to close the in-kernel Session, run a new one, redirect sys.stdout to capture TinyProfiler, and restart the Session. Two problems:
sys.stdout = capturedonly redirects the Python-level stream, so TinyProfiler output went to the real terminal and was lost.Fix: run one profiled solve in a short-lived subprocess. Python's
capture_output=Truegrabs fd 1 + fd 2 at the OS level, which captures everything TinyProfiler emits. The in-kernel Session is never touched, and the result dict is passed back via a__RESULT__JSON line.Also: expand the §7 markdown to explain the subprocess rationale and set expectations that TinyProfiler will break down the HYPRE solve (which §3 already showed is 96%+ of wall time).