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Reinstate preloading of some dll imports I've now come around to the conclusion that there is a justification for pre-loading the synchronization functions `WaitOnAddress` and `WakeByAddressSingle`. I've found this to have a particularly impact in testing frameworks that may have short lived processes which immediately spawn lots of threads. Also, because pre-main initializers imply a single-threaded environment, we can switch back to using relaxed atomics which might be a minor perf improvement on some platforms (though I doubt it's particularly notable). r? ``@Mark-Simulacrum`` and sorry for the churn here. For convenience I'll summarise previous issues with preloading and the solutions that are included in this PR (if any): **Issue:** User pre-main initializers may be run before std's **Solution:** The std now uses initializers that are guaranteed to run earlier than the old initializers. A note is also added that users should not copy std's behaviour if they want to ensure they run their initializers after std. **Issue:** Miri does not understand pre-main initializers. **Solution:** For miri only, run the function loading lazily instead. **Issue:** We should ideally use `LoadLibrary` to get "api-ms-win-core-synch-l1-2-0". Only "ntdll" and "kernel32" are guaranteed to always be loaded. **Solution:** None. We can't use `LoadLibrary` pre-main. However, in the past `GetModuleHandle` has always worked in practice so this should hopefully not be a problem. If/when Windows 7 support is dropped, we can finally remove all this for good and just use normal imports. |
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