fix(ex): propagate handler exceptions out of run_async#314
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The run_async trampoline caught and discarded every exception in its unhandled_exception(), so an error handler that rethrew (and the default handler, which rethrows by design) had no way to surface a task failure. The documented "exceptions are rethrown" behavior never happened. Rethrow from the trampoline instead, so an exception escaping a handler propagates out of the call that resumes the task rather than being swallowed. A rethrowing unhandled_exception leaves the trampoline suspended at its final suspend point, so the suspend_never final_suspend never self-destroys the frame. Fire-and-forget launch has no later owner, so operator() reclaims the frame when the inline dispatch unwinds, before propagating. Cooperative cancellation is reported by quitter as a stop_requested_exception sentinel through the same exception() channel. That is a normal completion, not an error, so the default handler discards the sentinel and rethrows everything else; otherwise a stopped quitter with no error handler would terminate. The result-only handler delegates to the same logic. Add tests covering propagation through both trampoline allocators (default memory_resource and value allocator), a rethrowing error handler, and a stopped quitter under the default handler.
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GCOVR code coverage report https://314.capy.prtest3.cppalliance.org/gcovr/index.html Build time: 2026-06-15 18:30:05 UTC |
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## develop #314 +/- ##
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Coverage 98.09% 98.10%
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Files 164 164
Lines 8873 8896 +23
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+ Hits 8704 8727 +23
Misses 169 169
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2 participants
Resolves #259.
The run_async trampoline caught and discarded every exception in its unhandled_exception(), so an error handler that rethrew (and the default handler, which rethrows by design) had no way to surface a task failure. The documented "exceptions are rethrown" behavior never happened.
Rethrow from the trampoline instead, so an exception escaping a handler propagates out of the call that resumes the task rather than being swallowed.
A rethrowing unhandled_exception leaves the trampoline suspended at its final suspend point, so the suspend_never final_suspend never self-destroys the frame. Fire-and-forget launch has no later owner, so operator() reclaims the frame when the inline dispatch unwinds, before propagating.
Cooperative cancellation is reported by quitter as a stop_requested_exception sentinel through the same exception() channel. That is a normal completion, not an error, so the default handler discards the sentinel and rethrows everything else; otherwise a stopped quitter with no error handler would terminate. The result-only handler delegates to the same logic.
Add tests covering propagation through both trampoline allocators (default memory_resource and value allocator), a rethrowing error handler, and a stopped quitter under the default handler.