💥 C Bridge: Custom slot supplier rework #1025
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Sushisource
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Oct 1, 2025
| drop(unsafe { Arc::from_raw(completion_ctx) }); | ||
| true | ||
| } | ||
| SlotReserveOperationState::Pending => false, |
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According to the docstring seems like this should also be a panic? It does seem wrong to call this if the cancel didn't happen
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While it could panic, there is no reason to panic as no invariants have been broken. Safely returning false here may make it easier to make the implementation safe. The other branch panics because it potentially reads from freed memory.
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I revised the docstring to make the intention clearer.
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What was changed
💥 BREAKING CHANGE: Redesigned the code flow around custom slot supplier in C bridge to ensure memory safety in case of cancellation. From Lang's point of view it works mostly the same as before, with the following differences:
user_dataargument (not used by .Net implementation but very useful for other languages).reserve, thectxargument is short-lived, andcompletion_ctxreplacessender.token_sourceis removed fromSlotReserveCtxand functiontemporal_core_set_reserve_cancel_targetis removed.cancel_reservetakescompletion_ctxargument instead oftoken_source.temporal_core_complete_async_reserveis safe to call after cancellation, making it possible to avoid race condition. This function now returns bool indicating whether the reservation was completed or cancelled.temporal_core_complete_async_cancel_reservethat has to be called after cancellation to clean up resources.Additionally, implemented
available_slotsfunctionality, and renamed the callback type aliases to make their relation toCustomSlotSupplierCallbacksmore obvious.There is a matching PR in .Net SDK that implements the new API: temporalio/sdk-dotnet#532
Why?
The previous implementation had memory corruption bugs, see temporalio/sdk-dotnet#458
Checklist
Part of [Bug] Issues with ReserveCtxFromBridge sdk-dotnet#458
How was this tested:
There is no test for the original bug. Due to the nature of this bug, it's impossible to write a test that reliably triggers the problematic conditions. The fix can be verified over time by the lack of transient CI failures in .Net SDK caused by this bug.
General tests of the custom slot supplier exercising these APIs are done inside .Net SDK, see temporalio/sdk-dotnet#532