This builds on the earlier thread safety work to make it so that setting the odb, index, refdb, or config for a repository is done in a threadsafe manner with minimized locking time. This is done by adding a lock to the repository object and using it to guard the assignment of the above listed pointers. The lock is only held to assign the pointer value. This also contains some minor fixes to the other work with pack files to reduce the time that locks are being held to and fix an apparently memory leak.
Implicit type conversion argument of function to size_t type Suspicious sequence of types castings: size_t -> int -> size_t Consider reviewing the expression of the 'A = B == C' kind. The expression is calculated as following: 'A = (B == C)' Unsigned type is never < 0
As a function that appears to only be called on error paths, I don't think it makes sense for it to return an error, or clobber the global giterr. Note that no existing callsites actually check the return code. In my own application, there are errors where the real error ends up being hidden, as git_mwindow_file_deregister() clobbers the global giterr. I'm not sure this error is even relevant?
Up to now, the idea was that the user would do all the operations for one repository in the same thread. Thus we could have the memory-mapped window information thread-local and avoid any locking. This is not practical in a few environments, such as Apple's GCD which allocates threads arbitrarily or the .NET CLR, where the OS-level thread can change at any moment. Make the control structure global and protect it with a mutex so we don't depend on the thread currently executing the code.
Once a file is registered, there is no way to deregister it, even after the structure that contains it is no longer needed and has been freed. This may be the source of #624. Allow and use the deregister function to remove our file from the global list.
On RAM: the .idx and .pack files become links to a .lock and the original download respectively. Assume some feature (such as record locking) supported by SFS but not JXFS or RAM: is required.