From 1a652df64325acc38783cf8a66cbf53fa706bacb Mon Sep 17 00:00:00 2001
From: Claes Redestad <redestad@openjdk.org>
Date: Sat, 17 Dec 2016 12:59:15 +0100
Subject: [PATCH] 8171373: Reduce copying during initialization of ModuleHashes

Reviewed-by: alanb, mchung, chegar
---
 .../jdk/internal/module/ModuleHashes.java        | 10 ++++------
 .../jdk/internal/module/SystemModuleFinder.java  | 16 ++++++++++++++--
 .../internal/plugins/SystemModulesPlugin.java    |  3 ++-
 3 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/jdk/src/java.base/share/classes/jdk/internal/module/ModuleHashes.java b/jdk/src/java.base/share/classes/jdk/internal/module/ModuleHashes.java
index 641127b894f..f4e5fcb9fe1 100644
--- a/jdk/src/java.base/share/classes/jdk/internal/module/ModuleHashes.java
+++ b/jdk/src/java.base/share/classes/jdk/internal/module/ModuleHashes.java
@@ -149,9 +149,10 @@ public final class ModuleHashes {
      */
     public static class Builder {
         final String algorithm;
-        Map<String, byte[]> nameToHash;
+        final Map<String, byte[]> nameToHash;
 
-        Builder(String algorithm) {
+        Builder(String algorithm, int initialCapacity) {
+            this.nameToHash = new HashMap<>(initialCapacity);
             this.algorithm =  Objects.requireNonNull(algorithm);
         }
 
@@ -159,9 +160,6 @@ public final class ModuleHashes {
          * Sets the module hash for the given module name
          */
         public Builder hashForModule(String mn, byte[] hash) {
-            if (nameToHash == null)
-                nameToHash = new HashMap<>();
-
             nameToHash.put(mn, hash);
             return this;
         }
@@ -170,7 +168,7 @@ public final class ModuleHashes {
          * Builds a {@code ModuleHashes}.
          */
         public ModuleHashes build() {
-            if (nameToHash != null) {
+            if (!nameToHash.isEmpty()) {
                 return new ModuleHashes(algorithm, nameToHash);
             } else {
                 return null;
diff --git a/jdk/src/java.base/share/classes/jdk/internal/module/SystemModuleFinder.java b/jdk/src/java.base/share/classes/jdk/internal/module/SystemModuleFinder.java
index cb7fa0a8d13..5ec0a62ca69 100644
--- a/jdk/src/java.base/share/classes/jdk/internal/module/SystemModuleFinder.java
+++ b/jdk/src/java.base/share/classes/jdk/internal/module/SystemModuleFinder.java
@@ -124,7 +124,7 @@ public class SystemModuleFinder implements ModuleFinder {
     private final Map<String, ModuleReference> nameToModule;
 
     // module name to hashes
-    private final Map<String, byte[]> hashes = new HashMap<>();
+    private final Map<String, byte[]> hashes;
 
     private SystemModuleFinder() {
         String[] names = moduleNames();
@@ -162,12 +162,24 @@ public class SystemModuleFinder implements ModuleFinder {
             }
         }
 
+        Map<String, byte[]> hashes = null;
+        boolean secondSeen = false;
         // record the hashes to build HashSupplier
         for (ModuleHashes mh : recordedHashes) {
             if (mh != null) {
-                hashes.putAll(mh.hashes());
+                // if only one module contain ModuleHashes, use it
+                if (hashes == null) {
+                    hashes = mh.hashes();
+                } else {
+                    if (!secondSeen) {
+                        hashes = new HashMap<>(hashes);
+                        secondSeen = true;
+                    }
+                    hashes.putAll(mh.hashes());
+                }
             }
         }
+        this.hashes = (hashes == null) ? Map.of() : hashes;
 
         ModuleReference[] mods = new ModuleReference[n];
 
diff --git a/jdk/src/jdk.jlink/share/classes/jdk/tools/jlink/internal/plugins/SystemModulesPlugin.java b/jdk/src/jdk.jlink/share/classes/jdk/tools/jlink/internal/plugins/SystemModulesPlugin.java
index 6adb3d699b5..d7cd59a398e 100644
--- a/jdk/src/jdk.jlink/share/classes/jdk/tools/jlink/internal/plugins/SystemModulesPlugin.java
+++ b/jdk/src/jdk.jlink/share/classes/jdk/tools/jlink/internal/plugins/SystemModulesPlugin.java
@@ -967,8 +967,9 @@ public final class SystemModulesPlugin implements Plugin {
                 hmv.visitTypeInsn(NEW, MODULE_HASHES_BUILDER);
                 hmv.visitInsn(DUP);
                 hmv.visitLdcInsn(recordedHashes.algorithm());
+                pushInt(hmv, ((4 * recordedHashes.names().size()) / 3) + 1);
                 hmv.visitMethodInsn(INVOKESPECIAL, MODULE_HASHES_BUILDER,
-                    "<init>", "(Ljava/lang/String;)V", false);
+                    "<init>", "(Ljava/lang/String;I)V", false);
                 hmv.visitVarInsn(ASTORE, BUILDER_VAR);
                 hmv.visitVarInsn(ALOAD, BUILDER_VAR);
             }