Add warnings for potential ergonomics failures for JDK8/Windows (#48968)

* Warn when MaxDirectMemorySize may be incorrect (Windows/JDK8 only issue) (#48365)

Our JVM ergonomics extract max heap size from JDK PrintFlagsFinal output. 
On JDK 8, there is a system-dependent bug where memory sizes are cast to 
32-bit integers. On affected systems (namely, Windows), when 1/4 of physical
memory is more than the maximum integer value, the output of PrintFlagsFinal
will be inaccurate. In the pathological case, where the max heap size would
be a multiple of 4g, the test will fail.

The practical effect of this bug, beyond test failures, is that we may set
MaxDirectMemorySize to an incorrect value on Windows. This commit adds a
warning about this situation during startup.

* Don't drop user's MaxDirectMemorySize flag on jdk8/windows (#48657)

* Always pass user-specified MaxDirectMemorySize

We had been testing whether a user had passed a value for
MaxDirectMemorySize by parsing the output of "java -XX:PrintFlagsFinal
-version". If MaxDirectMemorySize equals zero, we set it to half of max
heap. The problem is that on Windows with JDK 8, a JDK bug incorrectly
truncates values over 4g and returns multiples of 4g as zero. In order
to always respect the user-defined settings, we need to check our input
to see if an "-XX:MaxDirectMemorySize" value has been passed.

* Always warn for Windows/jdk8 ergo issue

Even if a user has set MaxDirectMemorySize, they aren't future-proof for
this JDK bug. With this change, we issue a general warning for the
windows/JDK8 issue, and a specific warning if MaxDirectMemorySize is
unset.

distribution/tools/launchers/src/main/java/org/elasticsearch/tools/launchers/JvmErgonomics.java

@@ -19,6 +19,8 @@
 
 package org.elasticsearch.tools.launchers;
 
+import org.elasticsearch.tools.java_version_checker.JavaVersion;
+
 import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStream;
@@ -57,7 +59,20 @@ static List<String> choose(final List<String> userDefinedJvmOptions) throws Inte
         final Map<String, Optional<String>> finalJvmOptions = finalJvmOptions(userDefinedJvmOptions);
         final long heapSize = extractHeapSize(finalJvmOptions);
         final long maxDirectMemorySize = extractMaxDirectMemorySize(finalJvmOptions);
-        if (maxDirectMemorySize == 0) {
+
+        if (System.getProperty("os.name").startsWith("Windows") && JavaVersion.majorVersion(JavaVersion.CURRENT) == 8) {
+            Launchers.errPrintln("Warning: with JDK 8 on Windows, Elasticsearch may be unable to derive correct");
+            Launchers.errPrintln("  ergonomic settings due to a JDK issue (JDK-8074459). Please use a newer");
+            Launchers.errPrintln("  version of Java.");
+        }
+
+        if (maxDirectMemorySize == 0 && userDefinedJvmOptions.stream().noneMatch(s -> s.startsWith("-XX:MaxDirectMemorySize"))) {
+
+            if (System.getProperty("os.name").startsWith("Windows") && JavaVersion.majorVersion(JavaVersion.CURRENT) == 8) {
+                Launchers.errPrintln("Warning: MaxDirectMemorySize may have been miscalculated due to JDK-8074459.");
+                Launchers.errPrintln("  Please use a newer version of Java or set MaxDirectMemorySize explicitly.");
+            }
+
             ergonomicChoices.add("-XX:MaxDirectMemorySize=" + heapSize / 2);
         }
         return ergonomicChoices;

distribution/tools/launchers/src/test/java/org/elasticsearch/tools/launchers/JvmErgonomicsTests.java

@@ -25,6 +25,7 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 import static org.hamcrest.Matchers.anyOf;
@@ -56,8 +57,8 @@ public void testExtractValidHeapSizeUsingMaxHeapSize() throws InterruptedExcepti
     }
 
     public void testExtractValidHeapSizeNoOptionPresent() throws InterruptedException, IOException {
-        // Muting on Windows, awaitsfix: https://github.com/elastic/elasticsearch/issues/47384
-        assumeFalse(System.getProperty("os.name").startsWith("Windows"));
+        // Muted for jdk8/Windows, see: https://github.com/elastic/elasticsearch/issues/47384
+        assumeFalse(System.getProperty("os.name").startsWith("Windows") && JavaVersion.majorVersion(JavaVersion.CURRENT) == 8);
         assertThat(
                 JvmErgonomics.extractHeapSize(JvmErgonomics.finalJvmOptions(Collections.emptyList())),
                 greaterThan(0L));
@@ -123,8 +124,9 @@ public void testExtractNoSystemProperties() {
         Map<String, String> parsedSystemProperties = JvmErgonomics.extractSystemProperties(Arrays.asList("-Xms1024M", "-Xmx1024M"));
         assertTrue(parsedSystemProperties.isEmpty());
     }
-    
+
     public void testMaxDirectMemorySizeChoice() throws InterruptedException, IOException {
+        // Muted for jdk8/Windows, see: https://github.com/elastic/elasticsearch/issues/47384
         assumeFalse(System.getProperty("os.name").startsWith("Windows") && JavaVersion.majorVersion(JavaVersion.CURRENT) == 8);
         final Map<String, String> heapMaxDirectMemorySize = new HashMap<>();
         heapMaxDirectMemorySize.put("64M", Long.toString((64L << 20) / 2));
@@ -141,8 +143,10 @@ public void testMaxDirectMemorySizeChoice() throws InterruptedException, IOExcep
     }
 
     public void testMaxDirectMemorySizeChoiceWhenSet() throws InterruptedException, IOException {
+        List<String> derivedSettingList = JvmErgonomics.choose(Arrays.asList("-Xms5g", "-Xmx5g", "-XX:MaxDirectMemorySize=4g"));
         assertThat(
-                JvmErgonomics.choose(Arrays.asList("-Xms1g", "-Xmx1g", "-XX:MaxDirectMemorySize=1g")),
+                derivedSettingList,
+                // if MaxDirectMemorySize is set, we shouldn't derive our own value for it
                 everyItem(not(startsWith("-XX:MaxDirectMemorySize="))));
     }