Hi all,

Enclosed is an RFC describing how we intend to allow users to disable file 
locking in HDF5. This currently only affects HDF5 1.10.0, but the HDF5 1.8 
branch will eventually be affected when we move some aspects of the file 
locking code over (TBD).

For those who are unfamiliar, file locking is used in HDF5 1.10.x to help users 
get SWMR semantics correct and prevent dangerous access patterns (e.g.: 
multiple simultaneous writers). It is not used to region-lock parts of the file 
as in some database systems. The main problem users have encountered is file 
locking being disabled on a file system, causing file lock calls to return 

For those who don't wish to read the entire document, our recommend solution is 

(a) Allow users to enable/disable the file locking via an environment variable.

(b) Update the library to emit a more informative error message when file 
locking appears to be unimplemented on a file system and the file lock call 

We discussed other options (new API calls, configure options, etc.) but an 
environment variable has the advantages of not requiring a library recompile or 
modifying existing source code as well as being fairly easy to implement.

Please let us know if you have any questions or concerns.

Dana Robinson
Software Engineer
The HDF Group

Attachment: RFC - Disable File Locking in HDF5 1.10 - v3.docx
Description: RFC - Disable File Locking in HDF5 1.10 - v3.docx

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