disallow reentrancy #380
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disallow reentrancy #380
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Marked draft to merge into 4.0 |
zah
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May 23, 2023
chronos/asyncloop.nim
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| doAssert not loop.polling, "The event loop and chronos functions in general are not reentrant" | ||
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| loop.polling = true | ||
| defer: loop.polling = false |
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I believe Chronos already needs to wrap every call to user-land in try/except, so why is it not possible to just set this flag there, just before entering user-land?
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Reentrancy causes event reordering and stack explosions, in addition to leading to hard-to-debug scenarios. Since none of chronos is actually tested under reentrant conditions (ie that all features such as exceptions, cancellations, buffer operations, timers etc work reliably when the loop is reentered), this is hard to support over time and prevents useful optimizations - this PR simply detects and disallows the behaviour to remove the uncertainty, simplifying reasoning about the event loop in general.
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Reentrancy causes event reordering and stack explosions, in addition to leading to hard-to-debug scenarios.
Since none of chronos is actually tested under reentrant conditions (ie that all features such as exceptions, cancellations, buffer operations, timers etc work reliably when the loop is reentered), this is hard to support over time and prevents useful optimizations - this PR simply detects and disallows the behaviour to remove the uncertainty, simplifying reasoning about the event loop in general.