Fix the ticker channel example giving wrong results on the website (#…

…4109)

https://play.kotlinlang.org/ of the example that's being changed
here is currently unreliable: the last line is occasionally `null`.

By increasing all time intervals twofold, we reduce the impact of
the CPU scheduling in the constrained environment. With this
change, the results are consistent across dozens of runs:
<https://pl.kotl.in/uCa-60j43>

Originally reported by `@PetrakovichVictoria`

docs/topics/channels.md

@@ -576,25 +576,25 @@ import kotlinx.coroutines.channels.*
 
 //sampleStart
 fun main() = runBlocking<Unit> {
-    val tickerChannel = ticker(delayMillis = 100, initialDelayMillis = 0) // create ticker channel
+    val tickerChannel = ticker(delayMillis = 200, initialDelayMillis = 0) // create a ticker channel
     var nextElement = withTimeoutOrNull(1) { tickerChannel.receive() }
     println("Initial element is available immediately: $nextElement") // no initial delay
 
-    nextElement = withTimeoutOrNull(50) { tickerChannel.receive() } // all subsequent elements have 100ms delay
-    println("Next element is not ready in 50 ms: $nextElement")
+    nextElement = withTimeoutOrNull(100) { tickerChannel.receive() } // all subsequent elements have 200ms delay
+    println("Next element is not ready in 100 ms: $nextElement")
 
-    nextElement = withTimeoutOrNull(60) { tickerChannel.receive() }
-    println("Next element is ready in 100 ms: $nextElement")
+    nextElement = withTimeoutOrNull(120) { tickerChannel.receive() }
+    println("Next element is ready in 200 ms: $nextElement")
 
     // Emulate large consumption delays
-    println("Consumer pauses for 150ms")
-    delay(150)
+    println("Consumer pauses for 300ms")
+    delay(300)
     // Next element is available immediately
     nextElement = withTimeoutOrNull(1) { tickerChannel.receive() }
     println("Next element is available immediately after large consumer delay: $nextElement")
     // Note that the pause between `receive` calls is taken into account and next element arrives faster
-    nextElement = withTimeoutOrNull(60) { tickerChannel.receive() } 
-    println("Next element is ready in 50ms after consumer pause in 150ms: $nextElement")
+    nextElement = withTimeoutOrNull(120) { tickerChannel.receive() }
+    println("Next element is ready in 100ms after consumer pause in 300ms: $nextElement")
 
     tickerChannel.cancel() // indicate that no more elements are needed
 }
@@ -610,11 +610,11 @@ It prints following lines:
 
 ```text
 Initial element is available immediately: kotlin.Unit
-Next element is not ready in 50 ms: null
-Next element is ready in 100 ms: kotlin.Unit
-Consumer pauses for 150ms
+Next element is not ready in 100 ms: null
+Next element is ready in 200 ms: kotlin.Unit
+Consumer pauses for 300ms
 Next element is available immediately after large consumer delay: kotlin.Unit
-Next element is ready in 50ms after consumer pause in 150ms: kotlin.Unit
+Next element is ready in 100ms after consumer pause in 300ms: kotlin.Unit
 ```
 
 <!--- TEST -->

kotlinx-coroutines-core/jvm/test/guide/example-channel-10.kt

@@ -5,25 +5,25 @@ import kotlinx.coroutines.*
 import kotlinx.coroutines.channels.*
 
 fun main() = runBlocking<Unit> {
-    val tickerChannel = ticker(delayMillis = 100, initialDelayMillis = 0) // create ticker channel
+    val tickerChannel = ticker(delayMillis = 200, initialDelayMillis = 0) // create a ticker channel
     var nextElement = withTimeoutOrNull(1) { tickerChannel.receive() }
     println("Initial element is available immediately: $nextElement") // no initial delay
 
-    nextElement = withTimeoutOrNull(50) { tickerChannel.receive() } // all subsequent elements have 100ms delay
-    println("Next element is not ready in 50 ms: $nextElement")
+    nextElement = withTimeoutOrNull(100) { tickerChannel.receive() } // all subsequent elements have 200ms delay
+    println("Next element is not ready in 100 ms: $nextElement")
 
-    nextElement = withTimeoutOrNull(60) { tickerChannel.receive() }
-    println("Next element is ready in 100 ms: $nextElement")
+    nextElement = withTimeoutOrNull(120) { tickerChannel.receive() }
+    println("Next element is ready in 200 ms: $nextElement")
 
     // Emulate large consumption delays
-    println("Consumer pauses for 150ms")
-    delay(150)
+    println("Consumer pauses for 300ms")
+    delay(300)
     // Next element is available immediately
     nextElement = withTimeoutOrNull(1) { tickerChannel.receive() }
     println("Next element is available immediately after large consumer delay: $nextElement")
     // Note that the pause between `receive` calls is taken into account and next element arrives faster
-    nextElement = withTimeoutOrNull(60) { tickerChannel.receive() } 
-    println("Next element is ready in 50ms after consumer pause in 150ms: $nextElement")
+    nextElement = withTimeoutOrNull(120) { tickerChannel.receive() }
+    println("Next element is ready in 100ms after consumer pause in 300ms: $nextElement")
 
     tickerChannel.cancel() // indicate that no more elements are needed
 }

kotlinx-coroutines-core/jvm/test/guide/test/ChannelsGuideTest.kt

@@ -113,11 +113,11 @@ class ChannelsGuideTest {
     fun testExampleChannel10() {
         test("ExampleChannel10") { kotlinx.coroutines.guide.exampleChannel10.main() }.verifyLines(
             "Initial element is available immediately: kotlin.Unit",
-            "Next element is not ready in 50 ms: null",
-            "Next element is ready in 100 ms: kotlin.Unit",
-            "Consumer pauses for 150ms",
+            "Next element is not ready in 100 ms: null",
+            "Next element is ready in 200 ms: kotlin.Unit",
+            "Consumer pauses for 300ms",
             "Next element is available immediately after large consumer delay: kotlin.Unit",
-            "Next element is ready in 50ms after consumer pause in 150ms: kotlin.Unit"
+            "Next element is ready in 100ms after consumer pause in 300ms: kotlin.Unit"
         )
     }
 }