Saturate overflowing values when adjusting time marks

KT-46132

libraries/stdlib/jvm/src/kotlin/time/MonoTimeSource.kt

@@ -5,23 +5,21 @@
 
 package kotlin.time
 
-import kotlin.time.Duration.Companion.nanoseconds
-
 @SinceKotlin("1.3")
 @ExperimentalTime
 internal actual object MonotonicTimeSource : TimeSource {
-    private fun read(): Long = System.nanoTime()
+    private val zero: Long = System.nanoTime()
+    private fun read(): Long = System.nanoTime() - zero
     override fun toString(): String = "TimeSource(System.nanoTime())"
 
     actual override fun markNow(): DefaultTimeMark = DefaultTimeMark(read())
-    actual fun elapsedFrom(timeMark: DefaultTimeMark): Duration = (read() - timeMark.reading).nanoseconds
+    actual fun elapsedFrom(timeMark: DefaultTimeMark): Duration =
+        saturatingDiff(read(), timeMark.reading)
 
-    // may have questionable contract
     actual fun adjustReading(timeMark: DefaultTimeMark, duration: Duration): DefaultTimeMark =
-        DefaultTimeMark(timeMark.reading + duration.inWholeNanoseconds)
+        DefaultTimeMark(saturatingAdd(timeMark.reading, duration))
 }
 
-
 @Suppress("ACTUAL_WITHOUT_EXPECT") // visibility
 internal actual typealias DefaultTimeMarkReading = Long
 

libraries/stdlib/jvm/test/time/TimeMarkJVMTest.kt

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package test.time
+
+import kotlin.test.*
+import kotlin.time.*
+import kotlin.time.Duration.Companion.nanoseconds
+
+@OptIn(ExperimentalTime::class)
+class TimeMarkJVMTest {
+
+    @Test
+    fun longDurationElapsed() {
+        TimeMarkTest().testLongDisplacement(TimeSource.Monotonic, { waitDuration -> Thread.sleep(waitDuration.inWholeMilliseconds) })
+    }
+
+    @Test
+    fun defaultTimeMarkAdjustmentInfinite() {
+        val baseMark = TimeSource.Monotonic.markNow()
+        val longDuration = Long.MAX_VALUE.nanoseconds
+
+        val pastMark = baseMark - longDuration
+        val infiniteFutureMark1 = pastMark + longDuration * 3
+
+        assertEquals(-Duration.INFINITE, infiniteFutureMark1.elapsedNow())
+    }
+
+}