[lucene] branch branch_9x updated: Add a sysprop "org.apache.lucene.store.MMapDirectory.enableMemorySegments" (#12062)

[us...@apache.org]

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uschindler pushed a commit to branch branch_9x
in repository https://gitbox.apache.org/repos/asf/lucene.git


The following commit(s) were added to refs/heads/branch_9x by this push:
     new cc85ca5d5b7 Add a sysprop "org.apache.lucene.store.MMapDirectory.enableMemorySegments" (#12062)
cc85ca5d5b7 is described below

commit cc85ca5d5b7760c967ff11f15675962bdfcd1911
Author: Uwe Schindler <us...@apache.org>
AuthorDate: Tue Jan 3 19:10:28 2023 +0100

    Add a sysprop "org.apache.lucene.store.MMapDirectory.enableMemorySegments" (#12062)
---
 lucene/CHANGES.txt                                 |  4 +++-
 .../org/apache/lucene/store/MMapDirectory.java     | 27 ++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 85273fdfe70..17f64af4290 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -71,7 +71,9 @@ New Features
 * GITHUB#12033: Support for Java 19 foreign memory support is now enabled by default,
   no need to pass "--enable-preview" on the command line. If exactly Java 19 is used,
   MMapDirectory will mmap Lucene indexes in chunks of 16 GiB (instead of 1 GiB) and
-  indexes closed while queries are running can no longer crash the JVM.  (Uwe Schindler)
+  indexes closed while queries are running can no longer crash the JVM.
+  To disable this feature, pass the following sysprop on Java command line:
+  "-Dorg.apache.lucene.store.MMapDirectory.enableMemorySegments=false" (Uwe Schindler)
 
 * GITHUB#11869: RangeOnRangeFacetCounts added, supporting numeric range "relationship" faceting over docvalue-stored
   ranges. (Marc D'Mello)
diff --git a/lucene/core/src/java/org/apache/lucene/store/MMapDirectory.java b/lucene/core/src/java/org/apache/lucene/store/MMapDirectory.java
index c50a6dd1a46..f251e536b72 100644
--- a/lucene/core/src/java/org/apache/lucene/store/MMapDirectory.java
+++ b/lucene/core/src/java/org/apache/lucene/store/MMapDirectory.java
@@ -22,6 +22,7 @@ import java.lang.invoke.MethodType;
 import java.nio.channels.ClosedChannelException; // javadoc @link
 import java.nio.file.Path;
 import java.util.Locale;
+import java.util.Optional;
 import java.util.concurrent.Future;
 import java.util.function.BiPredicate;
 import java.util.logging.Logger;
@@ -113,6 +114,17 @@ public class MMapDirectory extends FSDirectory {
    */
   public static final long DEFAULT_MAX_CHUNK_SIZE;
 
+  /**
+   * This sysprop allows to control if {@code MemorySegment} API should be used on supported Java
+   * versions. By default it is enabled; set to {@code false} to use legacy {@code ByteBuffer}
+   * implementation. On command line pass {@code
+   * -Dorg.apache.lucene.store.MMapDirectory.enableMemorySegments=false} to disable.
+   *
+   * @lucene.internal
+   */
+  public static final String ENABLE_MEMORY_SEGMENTS_SYSPROP =
+      "org.apache.lucene.store.MMapDirectory.enableMemorySegments";
+
   final int chunkSizePower;
 
   /**
@@ -369,7 +381,22 @@ public class MMapDirectory extends FSDirectory {
     }
   }
 
+  private static boolean checkMemorySegmentsSysprop() {
+    try {
+      return Optional.ofNullable(System.getProperty(ENABLE_MEMORY_SEGMENTS_SYSPROP))
+          .map(Boolean::valueOf)
+          .orElse(Boolean.TRUE);
+    } catch (
+        @SuppressWarnings("unused")
+        SecurityException ignored) {
+      return true;
+    }
+  }
+
   private static MMapIndexInputProvider lookupProvider() {
+    if (checkMemorySegmentsSysprop() == false) {
+      return new MappedByteBufferIndexInputProvider();
+    }
     final var lookup = MethodHandles.lookup();
     final int runtimeVersion = Runtime.version().feature();
     if (runtimeVersion == 19) {