Bert Huijben wrote:
-----Original Message----- From: Stefan Ruppert
[mailto:[email protected]] Sent: vrijdag 8 oktober 2010 17:55 To:
[email protected] Subject: Re: apr_file_*() threading issues under
Windows!
I do not use a file handle from different threads. But if this is
not a valid usage scenario why protected some piece of code with a
mutex??
Also a couple of weeks ago there was a discussion about performance
where these mutex operation are involved. Thus if the apr_file_*()
functions are designed to be not thread-safe, why use mutexes at
all??
I personally prefer that the application has to decide if it uses a
file from different threads and therefore has to protect the
operations by itselt.
In the early days of APR, httpd used threads on Windows and workers
on other systems. And most likely to keep things easy mutexes were
used to protect the file handles in some Windows scenarios. (If you
look at the history you will find that some other OSs had mutexes
too, but those were removed over the years)
The only documented safe way to use a file in multiple threads at
once (that should work on multiple Oss) is with APR_FOPEN_XTHREAD.
The mutexes are currently slowing down IO on Windows; especially on
multi CPU-systems, because they were simply never removed for
Windows. And I would really like to see them removed where possible.
(Ivan Zhakov already started working on this for some Subversion
performance critical code paths)
Ok, so from my point of view any mutex operation should only be used if
the APR_FOPEN_XTHREAD flag was specified. We at MyARM uses the
apr_file_*() API especially for an platform independend way to use file
locking. And we don't want the overhead of mutex operations which are
not needed!
I'll file a bug report to track this issue and add the appropriate patches.
Regards,
Stefan
