Re: [boost] [uuid] uuid::create() is extremely slow

From: Andy (atompkins_at_[hidden])
Date: 2007-06-01 13:13:01

"Jos Hickson" <jos.hickson_at_[hidden]> wrote in
news:fc03d05a0706010913l4865ef29re605685969592243_at_[hidden]: 

> On 01/06/07, Dave Jenkins <david_at_[hidden]> wrote:
>> Andy,
>> You did a nice job speeding up the uuid::create(engine) function to
>> 0.4 seconds for 1 million UUIDs.  But now the uuid::create() function
>> is extremely slow - 131 seconds for 1 million UUIDs (source code
>> below).  Can you change it to use a static mt19937 engine?

There was opposition to using static objects because of threading
concerns.  I do want a function that doesn't require the user to create
a random number generator themselves. 

If I use a static engine, I need to protect it with a mutex.  This is
not optimal because there is the overhead of locking and unlocking the
mutex.  Some people would rather have a static engine per thread using
thread local storage.  This still requires one to link with
Boost.Thread.  I created the uuid::create(Engine) function (great advice
from this list) so that users could do whatever they want (static engine
per thread, use thread local storage,...). 

The uuid::create() function should handle the common case and not be
best for all situations.  So, I guess I need help to determine what the
common case is. 

> 
> On a related note: doesn't reseeding the random number generator every
> time uuid::create() is called reduce the quality of the random numbers
> from the mt19937 engine?  

Probably.

> Doesn't the randomness then come from the
> seeding mechanism which is used?  So, on the whole it would indeed be
> better to use a static engine if possible.
> 
> Regards,
> 
> Jos
> 

Andy.