[fpc-devel] volatile variables

José Mejuto joshyfun at gmail.com
Tue Jun 28 16:13:57 CEST 2011

Hello FPC,

Tuesday, June 28, 2011, 3:39:29 PM, you wrote:

AB> Sort of right.  6 core system. Core 1 locks code block.  Code block
AB> should still use interlocked statements to make memory assignments so
AB> that when Core 1 releases lock - Core 2 can have a real-time image of
AB> variable.  Otherwise Core 2 may see a stale copy of the variable.

Core 2 should only access those variables using the same lock
(critical section) as core 1 or data integrity is not garanteed.

Critical sections garantee a full fence, pipe lines as invalidated.
The only possible problem is the variable caching in a register, but
as stated here the call to the function that perform the critical
section forces fpc to store the variables in a register to its memory
address and the critical section activity forces the fence ensuring
all cores see the same data at the same time.

You can not protect a code with a critical section and access the data
without using the same critical section, so you can not protect code
with a critical section and operate over the data in other thread with
interlock operations. This is not threading 101, do not ?

Best regards,

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