[6.0] Fix named mutexes on OSX to work between arm64 and emulated x64 processes

[kouvel]

• Port of Fix named mutexes on OSX to work between arm64 and emulated x64 processes #62764 to 6.0
• The page size is different between arm64 processes and emulated x64 processes
• The shared memory file size is set to the page size and there was a strict check on the file size, leading to an exception from the second process of a different arch that tries to share the same mutex
• Made the file size check less strict, and allowed an arch to increase but not decrease the file size such that it can be mapped at page size granularity
• Fixes Inter-process Mutex doesn't work for processes of different architectures on Apple Silicon #62140

Customer Impact

Some apps involving multiple processes may have x64 and arm64 .NET process components during transition, where the processes may try to share a named mutex for synchronization. Currently this is not possible, as the second process that tries to open an existing named mutex fails with an exception.

Regression?

No

Testing

Verified with a test case that a named mutex can be shared for synchronization between arm64 and emulated x64 .NET processes. Also verified backward compatibility between processes of the same arch.

Risk

Low, with a small caveat

• There is a case where this is not 100% compatible with an unfixed runtime when processes of different archs are trying to share the same mutex (in a scenario where it wouldn't have worked before the fix anyway). The fix allows an arm64 process to increase the shared memory file size to its page size such that it can be mapped. So for example, if an unfixed x64 process creates a named mutex, then a fixed arm64 process opens it (and increases the shared memory file size), then if an unfixed x64 process tries to open a new instance of the mutex it would throw an exception. It's expected that both runtimes are updated with the fix in order to interoperate successfully with named mutexes.

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Issue Details

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• Port of Fix named mutexes on OSX to work between arm64 and emulated x64 processes #62764 to 6.0
• The page size is different between arm64 processes and emulated x64 processes
• The shared memory file size is set to the page size and there was a strict check on the file size, leading to an exception from the second process of a different arch that tries to share the same mutex
• Made the file size check less strict, and allowed an arch to increase but not decrease the file size such that it can be mapped at page size granularity
• Fixes Inter-process Mutex doesn't work for processes of different architectures on Apple Silicon #62140

Author:	kouvel
Assignees:	kouvel
Labels:	area-System.Threading
Milestone:	6.0.x

[jeffschwMSFT]

Approved. We should consider for 6.0.x

[safern]

@jeffschwMSFT this still has servicing-consider is that an overlook, can I merge?

[jeffschwMSFT]

Not approved by tactics yet