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
