Add never, make control flow methods inline (#103)

Author: adamw

core/src/main/scala/ox/control.scala

@@ -1,20 +1,22 @@
 package ox
 
-def forever(f: => Unit): Nothing =
+import java.util.concurrent.locks.LockSupport
+
+inline def forever(f: => Unit): Nothing =
   while true do f
   throw new RuntimeException("can't get here")
 
 /** Repeat evaluating `f` while it evaluates to `true`. */
-def repeatWhile(f: => Boolean): Unit =
+inline def repeatWhile(f: => Boolean): Unit =
   var loop = true
   while loop do loop = f
 
 /** Repeat evaluating `f` until it evaluates to `true`. */
-def repeatUntil(f: => Boolean): Unit =
+inline def repeatUntil(f: => Boolean): Unit =
   var loop = true
   while loop do loop = !f
 
-def uninterruptible[T](f: => T): T =
+inline def uninterruptible[T](f: => T): T =
   scoped {
     val t = fork(f)
 
@@ -27,3 +29,9 @@ def uninterruptible[T](f: => T): T =
 
     joinDespiteInterrupted
   }
+
+/** Blocks the current thread indefinitely, until it is interrupted. */
+inline def never: Nothing = forever {
+  LockSupport.park()
+  if Thread.interrupted() then throw new InterruptedException()
+}

core/src/test/scala/ox/ControlTest.scala

@@ -42,4 +42,19 @@ class ControlTest extends AnyFlatSpec with Matchers {
 
     trail.get shouldBe Vector("no timeout", "done")
   }
+
+  it should "block a thread indefinitely" in {
+    val trail = Trail()
+    supervised {
+      fork {
+        never
+        trail.add("never happened!")
+      }
+
+      Thread.sleep(400)
+      trail.add("done")
+    }
+
+    trail.get shouldBe Vector("done")
+  }
 }

doc/control-flow.md

@@ -1,7 +1,11 @@
 # Control flow methods
 
-There are some helper methods which might be useful when writing forked code:
+There are some helper methods which might be useful when writing code using ox's concurrency operators:
 
 * `forever { ... }` repeatedly evaluates the given code block forever
 * `repeatWhile { ... }` repeatedly evaluates the given code block, as long as it returns `true`
+* `repeatUntil { ... }` repeatedly evaluates the given code block, until it returns `true`
 * `uninterruptible { ... }` evaluates the given code block making sure it can't be interrupted
+* `never` blocks the current thread indefinitely, until it is interrupted
+
+All of these are `inline` methods.