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Allow for the initial value of Ref to be GC'd #9733

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Merged
merged 1 commit into from
Mar 27, 2025
+31 −3
Merged

Allow for the initial value of Ref to be GC'd #9733

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25 changes: 24 additions & 1 deletion core-tests/shared/src/test/scala/zio/RefSpec.scala
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Original file line number Diff line number Diff line change
@@ -1,8 +1,11 @@
package zio

import zio.test.Assertion._
import zio.test.TestAspect._
import zio.test._

import scala.ref.WeakReference

object RefSpec extends ZIOBaseSpec {

def spec = suite("RefSpec")(
Expand Down Expand Up @@ -243,7 +246,27 @@ object RefSpec extends ZIOBaseSpec {
val result = typeCheck(""" Ref.make("").incrementAndGet """)
val expected = "value incrementAndGet is not a member of zio.UIO[zio.Ref[String]]"
assertZIO(result)(isLeft(startsWithString(expected)))
}
},
test("Initial value is GC'd") {
class Bar
ZIO.succeedUnsafe { implicit u =>
val n = 1000
var i = 0
val refs = Array.ofDim[Ref.Atomic[Bar]](n)
val weakRefs = Array.ofDim[WeakReference[Bar]](n)
while (i < n) {
val bar = new Bar()
val ref = Ref.unsafe.make(bar)
refs(i) = ref
weakRefs(i) = new WeakReference[Bar](bar)
ref.unsafe.set(null)
i += 1
}
java.lang.System.gc()

assertTrue(!weakRefs.exists(_.get.nonEmpty))
}
} @@ jvmOnly
)
)

Expand Down
9 changes: 7 additions & 2 deletions core/shared/src/main/scala/zio/Ref.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -374,8 +374,10 @@ object Ref extends Serializable {
def updateSomeAndGet(pf: PartialFunction[A, A])(implicit unsafe: Unsafe): A
}

val unsafe: UnsafeAPI =
new AtomicReference[A](initial) with UnsafeAPI { ref: AtomicReference[A] =>
val unsafe: UnsafeAPI = {
// NOTE: Instantiate the AtomicReference with a null and then set its value
// so that the initial value is not added as a class field allowing it to be GC'd
val ref0 = new AtomicReference[A]() with UnsafeAPI { ref: AtomicReference[A] =>
def get(implicit unsafe: Unsafe): A =
ref.asInstanceOf[AtomicReference[A]].get

Expand Down Expand Up @@ -436,6 +438,9 @@ object Ref extends Serializable {
.asInstanceOf[AtomicReference[A]]
.updateAndGet((current: A) => pf.applyOrElse(current, (_: Any) => current))
}
ref0.asInstanceOf[AtomicReference[A]].set(initial)
ref0
}

@deprecated("Kept for binary compatibility only. Do not use", "2.1.15")
private[zio] def value: AtomicReference[A] = unsafe.asInstanceOf[AtomicReference[A]]
Expand Down
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