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From: Piergiorgio Sartor
 <piergiorgio.sartor.this.should.not.be.used@nexgo.REMOVETHIS.de>
Newsgroups: comp.lang.python
Subject: Re: Best (simplest) way to share data between processes
Date: Sat, 6 Jul 2024 21:32:44 +0200
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On 06/07/2024 09.28, Chris Green wrote:
> I have a Raspberry Pi in my boat that uses I2C to read a number of
> voltages and currents (using ADS1115 A2D) so I can monitor the battery
> condition etc.
> 
> At present various different scripts (i.e. processes) just read the
> values using the I2C bus whenever they need to but I'm pretty sure
> this (quite rarely) results in false readings because two processes
> try to read at the same time.
> 
> Thus I'm looking for ways to prevent simultaneous access.

Why using "different scripts"?
Is it there any particular reason?

Maybe it would be better, if possible, to have
a single script, which, sequentially, reads
whatever needs to be read (or written).
In a loop.

This is even simpler than using a file.

bye,

pg

> One fairly obvious way is to have single process/script which reads
> the A2D values continuously and writes them to a file.  All other
> scripts then read from the file as needed, a simple file lock can then
> be used to prevent simultaneous access (well, simultaneous access when
> the writing process is writing).
> 
> Is this the simplest approach?  Are there better ways using
> multiprocess?  (They look more complicated though).
> 
> The I2C bus itself has a mutex but I don't think this guarantees that
> (for example) an A2D reading is atomic because one reading takes more
> than one I2C bus access.
> 
> Would a mutex of some sort around each I2C transaction (i.e. complete
> A2D reading) be a better way to go?
> 

-- 

piergiorgio