[Gllug] Programming: Atomic Increment/Decrement

[Jonathan Dye]

> -----Original Message-----
> From: Vincent AE Scott [mailto:gllug at codex.net]
> Sent: 07 August 2002 14:12
> To: gllug at linux.co.uk
> Subject: Re: [Gllug] Programming: Atomic Increment/Decrement
> 
> 
> Jonathan Dye(jonathan.dye at automationpartnership.com)@Wed, Aug 
> 07, 2002 at 01:58:10PM +0100:
> > Does anyone know if there are atomic increment/decrement 
> functions under
> > linux (or POSIX)?
> 
> isnt that what you use a mutex for?
> 
> pthread_mutex_init(3)

You _can_ use a mutex to protect the increment/decrement but it is usually
quite heavyweight.  A mutex is good if you are doing more than a simple
increment or decrement.

atomic increments/decrement (and for that matter mulitplications, devisions,
assignments, swaps etc) allow you to do things like reference counting in a
multi-threaded environment without the overhead of a mutex.  They increment
(or decrement) the counter and return the value (before or after depending
on impl) as a single uninterruptable operation.

If there is no suitable function then I will probably end up writing my own
using mutexes (or the most lightweigh synchronisation method that is
suitable).

JD


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