Run rollback code in ExplicitTxn dtor before clearing the currentTxn#5707
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Run rollback code in ExplicitTxn dtor before clearing the currentTxn#5707
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Cloudflare’s production implementation asserts that all SQLite operations occur with `currentTxn` set to either an ImplicitTxn or an ExplicitTxn. Previously, the ExplicitTxn dtor rolled back the transaction after setting the `currentTxn` to NoTxn, which caused the assertion to fail in certain workloads. The fix is to run the code that resets `currentTxn` after doing the rollback. I used Claude to find the bug, but the fix is my own.
justin-mp
commented
Dec 16, 2025
| } | ||
| ActorSqlite::ExplicitTxn::~ExplicitTxn() noexcept(false) { | ||
| [&]() noexcept { | ||
| KJ_DEFER([&]() noexcept { |
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It looks like this will run regardless of the KJ_DEFER? the lambda is called right away, which case would it not run?
KJ_DEFER runs the code in between the parens inside yet another lambda so the code itself doesn't get executed until leaving the scope by return or by exception. In kj's common.h:
#define KJ_DEFER(code) auto KJ_UNIQUE_NAME(_kjDefer) = ::kj::defer([&](){code;})
// Run the given code when the function exits, whether by return or exception.
Also why does this have to be a lambd in first place? Can just be normal code?
The lambda is marked noexcept (compared to noexcept(false) so that if the code throws in any way, it crashes the process. As the existing comment says, this was done to prevent dangling pointers.
shrima-cf
approved these changes
Dec 16, 2025
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Cloudflare’s production implementation asserts that all SQLite operations occur with
currentTxnset to either an ImplicitTxn or an ExplicitTxn. Previously, the ExplicitTxn dtor rolled back the transaction after setting thecurrentTxnto NoTxn, which caused the assertion to fail in certain workloads. The fix is to run the code that resetscurrentTxnafter doing the rollback.I used Claude to find the bug, but the fix is my own.