Experimental Physics and
Industrial Control System

Before starting on benjamin's message in details I do like "asyn" instead of "wait".
But perhaps callback is even better with callback=true meaning that link support will call a callback when the link completes. Either asyn or callback is better than wait.

The proposal to have just

process - boolean, i.e. should request be made to process record
wait - boolean, i.e. link is not complete until linked record completes processing
block - boolean, i.e. dont do any more record processing until link completes

Could be implemented easily as follows:

When link support returns it specifies 1) If wait is true, i.e. it will call a callback when the link completes and
2) If block is true. If wait is true Record support incremements a counter indicating how many callbacks are outstanding. If block is true, record support will not do any more record processing until all outstanding callbacks complete.

This is simple and efficient. Is it intuitive for the Application Developer?
With regards to the example of the array of processLink, I say yes.
The application developer has control of the order. If the definition is:

processLink = [3] {
       {pvname = "incA"; wait=true},
       {pvname = "incB"; wait=true,block=true},
       {pvname = "getSample"; wait=true;}
}

The link for getSample will not be requested until both incA and incB complete. I think this is intuitive.
There is a problem for separate link fields rather than an array of links.
Now the order in which the fields appear in the record matter. The order can never be changed or databases will break.

• The configuration has different lines  for "incA" and "incB", while in the course of record execution they are treated the same.
  The "block" statement in your example controls something that happens afterwards, it would logically apply to "incA" in the same fashion.
  It is really rather the "getSample" link whose execution is blocked until all previous records have finished.
  I see a good chance of confusion as the designer always has to remember: Does "block=true" mean that this record is blocked or that the next record is blocked?
• What happens if I set a link "wait=false, block=true"?
• Why doesn't the "getSample" have a "block=true" definition? Isn't further processing of the record held up until the processing is finished? Is "block=true" inherent for the last link in the array? Even if it is set "wait=false"?