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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Is a Boolean type inherently atomic ?
Date: Fri, 12 May 2023 20:38:29 +0300
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On 2023-05-12 15:17, Rod Kay wrote:
>     Surely only the least significant bit of the least significant byte 
> is relevant and so the value cannot be garbled by one task writing and 
> another reading at the same time ?


That seems very likely indeed, unless (as others have commented) the 
representation has been specified to use more bits. However, the Ada RM 
states in C.6(8/3) that "every atomic type or object is also defined to 
be volatile", and of course Boolean variables are not considered 
volatile unless they are specified to be Atomic or Volatile. So a 
Boolean type is not inherently atomic in the Ada RM sense of "atomic".

And of course if you use a shared variable to communicate data between 
tasks, that variable should be marked as Volatile, and there should also 
be some Atomic accesses to ensure that actions are "sequential", so 
marking the variable as Atomic is best.