full-disclosure - Re: readdir_r considered harmful

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Date: Tue Nov  8 03:27:14 2005
From: andrew at amxl.com (Andrew Miller)
Subject: Re: readdir_r considered harmful

Casper.Dik@....COM wrote:
...

>Had they done so, we would never have had to use readdir_r() and progammers
>would not have introduced bugs in the (mis)use of pathconf, over allocating,
>etc.
>
>I would be interested in seeing any real-world use of readdir_r() in
>a context where readdir_r() is required (multiple threads reading from
>a single DIR *).
>  
>
Consider the following situation(I'm not sure if anyone actually does this):
1) You have a "spool" directory containing a large number of files, each
which represents a task to process.
2) You have a number of worker threads. Each worker thread reads a file
from the global DIR*, and then opens and reads the file for
processing(and then loops on 2).

Of course, you could always just put a mutex around every call to
readdir(), and copy the filename somewhere safe, or you could invent a
signalling system to ask one thread to do all the readdir()s. Whether
this makes sense depends on how much of readdir_r has to be spent inside
a global mutex/spinlock anyway, and how long the processing part takes
compared with the readdir() part.

Andrew