[mono][threads] save/restore errno in thread state transitions #79856
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We already save/restore GetLastError on win32. Do it on posix platforms, too. If one thread is in a pinvoke wrapper, while another thread triggers a STW, the pinvoke wrapper will self-suspend the thread and wait for a notification to resume. Depending on the platform we can use win32 primitives, Mach semaphores or POSIX semaphores. win32 and posix can both change the value of last error (errno, respectively) while the thread is suspended. That means that code like this (generated by the LibraryImportAttribute source generator) cannot reliably retrieve the error from the last pinvoke: ```csharp __retVal = __PInvoke(__path_native, mode); // there is a pinvoke wrapper here, that transitions from GC Safe to GC Unsafe mode __lastError = System.Runtime.InteropServices.Marshal.GetLastSystemError(); ``` The solution is to explicitly preserve the value of GetLastError/errno when exiting from GC Safe. Fixes dotnet#77364
…RESTORE_POINT and W32_RESTORE_LAST_ERROR_FROM_RESTORE_POINT to MONO_RESTORE_LAST_ERROR_FROM_RESTORE_POINT
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I'm not sure there's a reliable test case to be made here. I'm going to try to make something with a pinvoke to a C function that always sets |
vargaz
approved these changes
Dec 20, 2022
This was referenced Dec 20, 2022
Closed
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I've tested this with dotnet8-preview1 on Alpine linux on ppc64le and s390x and this fixes the restore issue reliably. As for dotnet7, there's something missing for the bug to be fixed. |
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ping @lambdageek |
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/azp run runtime-extra-platforms |
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Azure Pipelines successfully started running 1 pipeline(s). |
This was referenced Jul 10, 2023
ghost
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When we exit from GC Safe to GC Unsafe mode, if there is a STW in progress, the thread will self-suspend. On some platforms, self-suspend is implemented using POSIX semaphores
sem_wait. Failures and spurious wakeups insem_waitmay changeerrno. That will make the following code (generated by theLibraryImportAttributesource generator) capture an incorrect error code:Note: we already had code to do this on win32 where APC calls can run on a suspended thread and change the value returned by
GetLastError. This PR expands the code for other platforms.Currently apple platforms use Mach semaphores (
semaphore_wait, etc) which do not pollute errno, so on those platforms we don't bother saving/restoring. If the thread state transition code changes to do additional work using other libc calls, we may need to revisit this.Fixes #77364