Scalatomic

Scalatomic is a Scala library that proposes an easy to use and hard to misuse API to manipulate atomic variables.

Usage

The main data type offered by the library is Atomic[A], which represents atomic variables with values of type A. One creates such variables using the newAtomic method:

val myAtomicVar: Atomic[Int] = newAtomic(0)

Atomic objects always hold a value. Therefore, at creation time, an initial value must be provided.

The value held by an atomic variable can be read using the read method:

val currentValue: Int = myAtomicVar.read

Instead of providing a low level instruction such as compareAndSet, the library offers the method modify to issue modification requests to the atomic variable. The method onFailure is called on the result of modify to handle failures due to concurrent accesses.

As an example, here is how to specify that we wish to increment by one the value held by myAtomicVar, but only if it is currently smaller than 10:

myAtomicVar modify { (value: Int) =>
    if (value < 10) {
        Update(value + 1)  // Requests the value to be updated.
    }
    else {
        NoUpdate  // No update is requested.
    }
} onFailure {
    retry  // In case of concurrent modification, retry.
}

It is also possible to return values from the modify / onFailure calls:

val result: String = myAtomicVar modify { (value: Int) =>
    if (value < 10) {
        Update(value + 1) withResult "Updated"
    }
    else {
        NoUpdate withResult "Not updated"
    }
} onFailure {
    "Update failed"
}