> This is the misunderstanding of the OP. The OP doesn't talk about the happens-before relationship; instead, the intention can be simplified as talking about whether the control flow executing a previous expression occurs in no later time point than the time point it executes a later expression.

Isn't "occurs in no later time point than the time point it executes a later expression" the definition of "happens-before"?


________________________________
From: Std-Discussion <std-discussion-bounces_at_lists.isocpp.org> on behalf of jim x via Std-Discussion <std-discussion_at_[hidden]>
Sent: Thursday, June 11, 2026 7:52:10 AM
To: std-discussion_at_[hidden] <std-discussion_at_[hidden]>
Cc: jim x <xmh970252187_at_gmail.com>
Subject: Re: [std-discussion] Does the C++ abstract machine recognize a temporal order of execution?


What exactly would you be establishing a happens-before relationship with in the original example?

This is the misunderstanding of the OP. The OP doesn't talk about the happens-before relationship; instead, the intention can be simplified as talking about whether the control flow executing a previous expression occurs in no later time point than the time point it executes a later expression.

On Thu, Jun 11, 2026 at 1:37 PM Jennifier Burnett via Std-Discussion <std-discussion_at_[hidden]<mailto:std-discussion_at_[hidden]>> wrote:
An acquire barrier is meaningless in this context. An acquire barrier needs either a release operation or atomic operation preceded by a release barrier to have any semantics beyond relaxed. What exactly would you be establishing a happens-before relationship with in the original example? Assuming the call to now() is an implicit acquire barrier changes nothing about the semantics because there's no corresponding release for it to establish a happens-before relationship with. The first thread doesn't even have any operations other than the call to now() that the acquire barrier would apply to

On 11 June 2026 01:37:42 BST, Thiago Macieira via Std-Discussion <std-discussion_at_[hidden]<mailto:std-discussion_at_[hidden]>> wrote:
>On Wednesday, 10 June 2026 16:24:30 Pacific Daylight Time Simon Cooke wrote:
>> If you don't want that, you need acquire semantics, which will prevent the
>> write from down after the timestamp() call in #2
>
>This is the essence of the argument: reading from the monotonic clock should
>be an acquire barrier. The Standard does not say it is, but I think it should.
>
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