Implement assert-based virtual locks on IDs

[mattjala]

Implement virtual locks for IDs

When the library is built in debug mode, H5I will track how many concurrent API routines reference application-exposed IDs passed in through the H5VL API, and throw an assertion if an ID is simultaneously provided to more library threads than its reference count permits. The purpose of this is to help multi-threaded application developers detect invalid API usage early on in development.

The virtual locks are implemented by allowing variants of the FUNC_ENTER and FUNC_LEAVE macros to take a variable numbers of IDs as additional arguments.

The _NOINIT enter/exit variants do not interact with the virtual locks, since routines using these macros generally aren't meant to be directly used by applications (e.g. the routines for passthrough VOLs in H5VLcallback.c).

There are a few other factors the virtual locks must consider which complicate the implementation somewhat:

• Default and library-created IDs (H5P_DEFAULT and predefined datatypes) aren't reference counted in the same way as other IDs, and so are ignored by the virtual locks.
• API routines that decrement the application ref count of a provided ID (e.g. H5VLunregister_connector()). If using a simple virtual lock scheme, a routine that decrements the app ref count before calling the virtual lock exit would create a region where another thread could, on entry, apparently find the ID exceeding its application reference count, even though the usage is valid. The solution is that routines which decrement the app ref count indicate that an "application unlock" has taken place on the ID. Verification of ID ref counts compare the virtual lock count to the sum of application references plus 'application unlocks'. The application unlock count also serves to prevent double-counting of virtual lock releases in H5I_vlock_exit().