Velocity Reviews - Computer Hardware Reviews

Velocity Reviews > Newsgroups > Programming > C++ > Blocking queue race condition?

Reply
Thread Tools

Blocking queue race condition?

 
 
Andrew Tomazos
Guest
Posts: n/a
 
      01-09-2012
On Jan 8, 11:02*pm, "Chris M. Thomasson" <(E-Mail Removed)> wrote:
> So, assuming that `sem_post/wait' have at least 1 atomic RMW each, I am
> counting:
>
> 5 atomic RMW for push and 5 atomic RMW for pop... Memory barriers aside for
> a moment...


The original (faulty) design had 3 atomics (CMPXCHG, XADD, CMPXCHG)
for push and the same for pop in the uncontended case.

> Even in the presence of ZERO contention, how can this possibly perform
> better than a simple condvar/mutex setup?


If by simple "condvar/mutex setup", you mean one giant lock for the
whole queue, consider that the real queue may have a complex
constructor and/or a large value type. A single lock forces
unnecessary serialization of readers and writers. Ideally you would
like readers and writers to have access to different cells in
parallel.

> The condvar/mutex will be using far less atomic RMW and memory barriers.


sem_post and sem_wait are implemented with a CMPXCHG in the
uncontended case on my target platform (x86_64 linux).
-Andrew.
 
Reply With Quote
 
 
 
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Program blocked in Queue.Queue.get and Queue.Queue.put Kris Python 0 01-04-2012 03:46 PM
Is Queue.Queue.queue.clear() thread-safe? Russell Warren Python 4 06-27-2006 03:03 PM
what's the difference between #include "queue.h" and #include "queue.cpp" Kceiw C++ 3 03-14-2006 03:01 AM
Queue.Queue-like class without the busy-wait Paul L. Du Bois Python 29 04-04-2005 01:28 PM
Mega Pixel race is like the Mhz Race Hugo Drax Digital Photography 7 01-12-2004 11:07 AM



Advertisments