[DOC]: barrier_arrive_tx docs need to specify how the count is updated

[gonzalobg]

Is this a duplicate?

• I confirmed there appear to be no duplicate issues for this bug and that I agree to the Code of Conduct

Is this for new documentation, or an update to existing docs?

New

Describe the incorrect/future/missing documentation

Instead of:

Arrives at a barrier in shared memory, updating both the arrival count and transaction count.

should say:

Arrives at a barrier in shared memory, decrementing the arrival count by arrive_count_update and incrementing the expected transaction count by transaction_count_update`.

This is covered in the effects but the summary should cover it to, since this API only arrives at the arrive-count; it does not "arrive" at the tx-count (complete-tx), it performs an expect-tx op on the tx-count.

If this is a correction, please provide a link to the incorrect documentation. If this is a new documentation request, please link to where you have looked.

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