Further improvements to testGuideCancelExample02/03 for stability

Author: elizarov

coroutines-guide.md

@@ -353,12 +353,13 @@ example shows:
 
 ```kotlin
 fun main(args: Array<String>) = runBlocking<Unit> {
+    val startTime = System.currentTimeMillis()
     val job = launch(CommonPool) {
-        var nextPrintTime = System.currentTimeMillis()
+        var nextPrintTime = startTime
         var i = 0
-        while (i < 10) { // computation loop
-            val currentTime = System.currentTimeMillis()
-            if (currentTime >= nextPrintTime) {
+        while (i < 10) { // computation loop, just wastes CPU
+            // print a message twice a second
+            if (System.currentTimeMillis() >= nextPrintTime) {
                 println("I'm sleeping ${i++} ...")
                 nextPrintTime += 500L
             }
@@ -393,18 +394,19 @@ There are two approaches to making computation code cancellable. The first one i
 invoke a suspending function. There is a [yield] function that is a good choice for that purpose.
 The other one is to explicitly check the cancellation status. Let us try the later approach. 
 
-Replace `while (true)` in the previous example with `while (isActive)` and rerun it. 
+Replace `while (i < 10)` in the previous example with `while (isActive)` and rerun it. 
 
 ```kotlin
 fun main(args: Array<String>) = runBlocking<Unit> {
+    val startTime = System.currentTimeMillis()
     val job = launch(CommonPool) {
-        var nextPrintTime = 0L
+        var nextPrintTime = startTime
         var i = 0
         while (isActive) { // cancellable computation loop
-            val currentTime = System.currentTimeMillis()
-            if (currentTime >= nextPrintTime) {
+            // print a message twice a second
+            if (System.currentTimeMillis() >= nextPrintTime) {
                 println("I'm sleeping ${i++} ...")
-                nextPrintTime = currentTime + 500L
+                nextPrintTime += 500L
             }
         }
     }

kotlinx-coroutines-core/src/test/kotlin/guide/example-cancel-02.kt

@@ -20,12 +20,13 @@ package guide.cancel.example02
 import kotlinx.coroutines.experimental.*
 
 fun main(args: Array<String>) = runBlocking<Unit> {
+    val startTime = System.currentTimeMillis()
     val job = launch(CommonPool) {
-        var nextPrintTime = System.currentTimeMillis()
+        var nextPrintTime = startTime
         var i = 0
-        while (i < 10) { // computation loop
-            val currentTime = System.currentTimeMillis()
-            if (currentTime >= nextPrintTime) {
+        while (i < 10) { // computation loop, just wastes CPU
+            // print a message twice a second
+            if (System.currentTimeMillis() >= nextPrintTime) {
                 println("I'm sleeping ${i++} ...")
                 nextPrintTime += 500L
             }

kotlinx-coroutines-core/src/test/kotlin/guide/example-cancel-03.kt

@@ -20,14 +20,15 @@ package guide.cancel.example03
 import kotlinx.coroutines.experimental.*
 
 fun main(args: Array<String>) = runBlocking<Unit> {
+    val startTime = System.currentTimeMillis()
     val job = launch(CommonPool) {
-        var nextPrintTime = 0L
+        var nextPrintTime = startTime
         var i = 0
         while (isActive) { // cancellable computation loop
-            val currentTime = System.currentTimeMillis()
-            if (currentTime >= nextPrintTime) {
+            // print a message twice a second
+            if (System.currentTimeMillis() >= nextPrintTime) {
                 println("I'm sleeping ${i++} ...")
-                nextPrintTime = currentTime + 500L
+                nextPrintTime += 500L
             }
         }
     }