CODEWITHSUNDEEP
sbt
NSF
NSF

Reputation: 2549

How to prevent sbt from running a task multiple times in a session?

I'd like to prevent the following task from getting run multiple times when sbt is running:

val myTask = someSettings map {s => if !s.isDone doSomethingAndSetTheFlag}

So what's expected would be when myTask is run for the first time, isDone is false and something gets done in the task, and then the task sets the flag to true. But when the task is run for the second time, since the isDone flag is true, it skips the actual execution block.

The expected behavior is similar to compile -> when source is compiled, the task doesn't compile the code again the next time it's triggered until watchSource task says the code has been changed.

Is it possible? How?

Upvotes: 1

Views: 382

Answers (1)

lpiepiora
lpiepiora

Reputation: 13749

This is done by sbt, a task will be evaluated only once within a single run. If you want to have a value evaluated once, at the project load time, you can change it to be a SettingKey.

This is documented in the sbt documentation (highlighting is mine):

As mentioned in the introduction, a task is evaluated on demand. Each time sampleTask is invoked, for example, it will print the sum. If the username changes between runs, stringTask will take different values in those separate runs. (Within a run, each task is evaluated at most once.) In contrast, settings are evaluated once on project load and are fixed until the next reload.

Upvotes: 1

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