HAVE_DD_LOCK

[Jeff Johnston]

The code that uses HAVE_DD_LOCK in libc/posix was taken from an existing 
code base (IIRC FreeBSD).

The code in libc/posix is offered optionally to platforms.  The dir 
family routines code there can be ignored if the platform already 
supplies these functions (via the flag HAVE_OPENDIR).  If not 
short-circuited via HAVE_OPENDIR, a port must implement sys/dirent.h or 
else the code will not build to begin with as you are probably already 
well-aware.  A platform can also build these and also override them in 
either the libc/machine/xxx or libc/sys/xxxx directories.

So, if you choose to build the functions in libc/posix for your platform 
and you do not short-circuit them with HAVE_OPENDIR and do not override 
them yourself in your libc/sys directory and you support 
multi-threading, then you had either better implement the dd_lock field 
and set HAVE_DD_LOCK or else document that those functions are not 
thread-safe.

-- Jeff J.

Neal H. Walfield wrote:
> I'm trying to understand the purpose of HAVE_DD_LOCK.  It seems to me
> either the library is multi-threaded, in which case the locking
> functionality described in libc/include/sys/lock.h must be provided
> and not locking is a bug, or the library is single-threaded, in which
> case, the locking primitives a no-ops.
> 
> Thanks,
>