Re: [boost] Re: New file uploaded to boost

From: Iain.Hanson_at_[hidden]
Date: 2001-05-23 10:49:21

     Hi,
     
     It looks to me as though atomic_t should be templatedised on value 
     type. This would have the advantage of shrinking its memory footprint 
     to those member fuctions used.
     
     What behavior would you want of a counter once it reached the max 
     value for the value type. Should it wrap or latch?
     
     Which additional operations do you need on a counter? Normally, 
     counters can have an arbitary value added or subtracted in addition to 
     inc and dec, but it does not normally make sense to negate or 
     otherwise perform bitwise operations on a counter?
     
     /ikh

______________________________ Reply Separator _________________________________
Subject: Re: [boost] Re: New file uploaded to boost
Author:  bdawes (bdawes_at_[hidden]) at unix,mime
Date:    22/05/01 22:27

At 04:09 PM 5/22/2001, williamkempf_at_[hidden] wrote:
     
 >> The one need that keeps coming up is thread-safe counter known to 
 >hold at
 >> least 32 bits.
 >
 >If we were to limit it I'd think it would be better to say at least 
 >sizeof(int) bits.  I'm sure there are some architectures that would 
 >allow for efficient 16 bit atomic operations since an int is 16 bit 
 >there, while 32 bit atomic types would have to rely on the much 
 >slower mutex.  At this point atomic_t could fit this bill simply by 
 >changing the documentation (i.e. the current implementation fits the 
 >bill any way).
     
I've run into the need for about a dozen counters now, and every one of 
them had to be at least 32 bits.  Slow, fast, it didn't matter, they had to 
be at least 32 bits even on platforms where int is 16 bits.
     
The whole thing with atomic_t might be a red herring.  It may well be that 
thread_safe_int_least32_t needs a full set of integer operations.  So even 
if sizeof(int)==32, it can't just be a typedef for atomic_t.
     
--Beman
     
     
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