Volodya, Thanks for answer. Right I have forgotten to put the subject->it was stupid. But the try_mutex and scoped_tyy_lock cause that both processors are used properly. Can you explain? Thank you in advance. Pshemek -----Original Message----- From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Vladimir Prus Sent: 22 April 2005 13:13 To: boost-users@lists.boost.org Subject: [Boost-users] Mutexes (Was: (no subject)) Hi Przemyslaw, (btw, it's better to give some subject to postings).

I have found a very strange behaviour (for me at least!) in boost.Thread. The same dummy code: boost::mutex M;

void functionA(int j)

{

for(int i=0; i

{

boost::mutex::scoped_lock lock(M);

And it would be good if the code was properly indented.

sqrt(static_cast<double>(i));

void functionB(int j)

{

for(int i=0; i

{

boost::mutex::scoped_lock lock(M); ..... If we do not lock the mutex then both processors are used on 100%. However, in case the line is uncommented (we lock the mutex) only one processor is used.

If you lock the mutex, then only one thread can be inside loop body at the moment. Since the code outside of mutex is very small, most of the time only one thread will be running. So, it's reasonable that OS uses just one processor. - Volodya _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users -------------------------------------------------------- If you are not an intended recipient of this e-mail, please notify the sender, delete it and do not read, act upon, print, disclose, copy, retain or redistribute it. Click here for important additional terms relating to this e-mail. http://www.ml.com/email_terms/ --------------------------------------------------------