read
Read the value from a TVar.
import arrow.fx.stm.TVar
import arrow.fx.stm.atomically
suspend fun main() {
//sampleStart
val tvar = TVar.new(10)
val result = atomically {
tvar.read()
}
//sampleEnd
println(result)
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This comes with a few guarantees:
Any given TVar is only ever read once during a transaction.
When committing the transaction the value read has to be equal to the current value otherwise the transaction will retry
Read a value from a TMVar without removing it.
import arrow.fx.stm.TMVar
import arrow.fx.stm.atomically
suspend fun main() {
//sampleStart
val tmvar = TMVar.new(30)
val result = atomically {
tmvar.read()
}
//sampleEnd
println("Result $result")
println("New value ${atomically { tmvar.tryTake() } }")
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This retries if the TMVar is empty but does not take the value out if it succeeds.
See also
for a version that does not retry.
Remove the front element from the TQueue or retry if the TQueue is empty.
import arrow.fx.stm.TQueue
import arrow.fx.stm.atomically
suspend fun main() {
//sampleStart
val tq = TQueue.new<Int>()
val result = atomically {
tq.write(2)
tq.read()
}
//sampleEnd
println("Result $result")
println("Items in queue ${atomically { tq.flush() }}")
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See also
for a version that does not retry.
for a version that does not remove the element.