[5.3][Serialization] Add option to load swiftmodule files as volatile and avoid mmap #33172
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Avoid mmaping swiftmodule files to hopefully fix issues seen when building many Swift projects in parallel on NFS. This only affects loading ModuleFile, it doesn't affect scanning swiftmodule for dependecies which are still handled as non-volatile. rdar://63755989
Introduce a new frontend flag -enable-volatile-modules to trigger loading swiftmodule files as volatile and avoid using mmap. Revert the default behavior to using mmap. rdar://63755989
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@swift-ci Please test |
nkcsgexi
approved these changes
Jul 28, 2020
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@swift-ci Please nominate |
DougGregor
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Jul 29, 2020
AnthonyLatsis
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swift 5.3
🍒 release cherry pick
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Swiftmodule files are loaded with mmap when read by a client for deserialization. This can lead to crashes when building Swift projects in parallel if a client is reading from a swiftmodule file while the project installing it replaces the file. This PR adds a frontend flag to force loading swiftmodule files as volatile and avoid mmap.