Re: apr_file_* weirdness on Mac OS X

[Gordon Henriksen]

On 2008-10-03, at 02:40, Tim Bray wrote:

I'm developing a module which accepts a large number of POST  
requests, receives the request bodies, and persists them into  
ordinary files in the filesystem.  On OS X, there are occasions  
where the file is (rarely) transiently not there.  The idiom looks  
like this

Same code running in -X single-threaded mode, no problem.  Same code  
on Solaris, no problem.  (Well, yes, there are other weird Solaris  
problems with mutexes, but we'll get to those).


Sounds like a race. I'd suggest you replace this:

   status = apr_file_open(&fp, tempname, APR_FOPEN_WRITE |  
APR_FOPEN_CREATE,
                          PERMS, pool);

with

apr_status_t status;
do {
  ... generate random filename ...
  status = apr_file_open(..., APR_FOPEN_WRITE|APR_FOPEN_CREATE| 
APR_FOPEN_EXCL, ...);
} while (APR_IS_EEXIST(status));

in order to hedge against another thread operating on the same  
filename concurrently. apr_file_mktemp will handle this detail  
transparently for you.

— Gordon