The common convention in C APIs is to have a return value that indicates
failure, usually -1 or NULL. The caller checks errno only if the return
value indicates failure.
This appears to be the convention followed in the published API, in most
places. Functions returning 'void' like 'dfsCreateDirectory' should
probably return ints with 0 indicating success and -1 indicating failure.
I also notice 'bool' being returned by a couple of functions, these
should return ints as well.
Doug Cutting wrote:
The spec says:
/** All APIs set errno to meaningful values */
So callers should always check errno after each call. Whether this is
the best way to handle errors in C can be debated, but an error
mechanism was in fact specified.
Doug
Konstantin Shvachko wrote:
I think this a very important issue raised by David.
IMO __ALL__ functions should return an integer value indicating
success (=0) or failure (<0).
Unless we want to use C style Exceptions, otherwise we won't be able
to identify what went
wrong if anything.
NULL or bool is not enough in most cases, since we need to distinguish
e.g. between
timeout (when we retry) and "file not found" cases.
The actual return objects should be passed as outputs parameters.
E.g.
dfsFS dfsConnect(char *host, tPort port);
will become
tCompletionCode dfsConnect(char *host, tPort port, dfsFS fileSystem );
where tCompletionCode could be integer for now. Or we can define a
structure
{ int errCode; char *errDescription; }
to return the actual error descriptions along with the error code.
--Konstantin
Devaraj Das wrote:
Do dfsConnect and dfsOpenFile return NULL on failure?
Yes.
Shouldn't dfsSeek, dfsRename, dfsCreateDirectory and
dfsSetWorkingDirectory each have a return value to indicate success
or failure? Or are they assumed to never fail?
Yes these functions should have return values. I will update the API
spec.
Thanks for pointing this out.
-----Original Message-----
From: David Bowen [mailto:[EMAIL PROTECTED] Sent: Monday, May 01,
2006 8:13 AM
To: [email protected]
Subject: Re: C API for Hadoop DFS
I'm curious about error handling.
Do dfsConnect and dfsOpenFile return NULL on failure?
Shouldn't dfsSeek, dfsRename, dfsCreateDirectory and
dfsSetWorkingDirectory each have a return value to indicate success
or failure? Or are they assumed to never fail?
- David
