src/share/vm/classfile/stringTable.cpp

rev 12679 : 8176593: Throwable::getStackTrace performance regression
Reviewed-by: jiangli, iklam, coleenp, sspitsyn

@@ -1,7 +1,7 @@
 /*
- * Copyright (c) 1997, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.

@@ -94,14 +94,18 @@
 
 CompactHashtable<oop, char> StringTable::_shared_table;
 
 // Pick hashing algorithm
 unsigned int StringTable::hash_string(const jchar* s, int len) {
-  return use_alternate_hashcode() ? AltHashing::murmur3_32(seed(), s, len) :
+  return use_alternate_hashcode() ? alt_hash_string(s, len) :
                                     java_lang_String::hash_code(s, len);
 }
 
+unsigned int StringTable::alt_hash_string(const jchar* s, int len) {
+  return AltHashing::murmur3_32(seed(), s, len);
+}
+
 unsigned int StringTable::hash_string(oop string) {
   EXCEPTION_MARK;
   if (string == NULL) {
     return hash_string((jchar*)NULL, 0);
   }

@@ -115,15 +119,14 @@
     vm_exit_out_of_memory(length, OOM_MALLOC_ERROR, "unable to create Unicode string for verification");
     return 0;
   }
 }
 
-oop StringTable::lookup_shared(jchar* name, int len) {
-  // java_lang_String::hash_code() was used to compute hash values in the shared table. Don't
-  // use the hash value from StringTable::hash_string() as it might use alternate hashcode.
-  return _shared_table.lookup((const char*)name,
-                              java_lang_String::hash_code(name, len), len);
+oop StringTable::lookup_shared(jchar* name, int len, unsigned int hash) {
+  assert(hash == java_lang_String::hash_code(name, len),
+         "hash must be computed using java_lang_String::hash_code");
+  return _shared_table.lookup((const char*)name, hash, len);
 }
 
 oop StringTable::lookup_in_main_table(int index, jchar* name,
                                 int len, unsigned int hash) {
   int count = 0;

@@ -154,11 +157,11 @@
   // Check if the symbol table has been rehashed, if so, need to recalculate
   // the hash value and index before second lookup.
   unsigned int hashValue;
   int index;
   if (use_alternate_hashcode()) {
-    hashValue = hash_string(name, len);
+    hashValue = alt_hash_string(name, len);
     index = hash_to_index(hashValue);
   } else {
     hashValue = hashValue_arg;
     index = index_arg;
   }

@@ -197,32 +200,38 @@
   }
 #endif
 }
 
 oop StringTable::lookup(jchar* name, int len) {
-  oop string = lookup_shared(name, len);
+  // shared table always uses java_lang_String::hash_code
+  unsigned int hash = java_lang_String::hash_code(name, len);
+  oop string = lookup_shared(name, len, hash);
   if (string != NULL) {
     return string;
   }
-
-  unsigned int hash = hash_string(name, len);
+  if (use_alternate_hashcode()) {
+    hash = alt_hash_string(name, len);
+  }
   int index = the_table()->hash_to_index(hash);
   string = the_table()->lookup_in_main_table(index, name, len, hash);
 
   ensure_string_alive(string);
 
   return string;
 }
 
 oop StringTable::intern(Handle string_or_null, jchar* name,
                         int len, TRAPS) {
-  oop found_string = lookup_shared(name, len);
+  // shared table always uses java_lang_String::hash_code
+  unsigned int hashValue = java_lang_String::hash_code(name, len);
+  oop found_string = lookup_shared(name, len, hashValue);
   if (found_string != NULL) {
     return found_string;
   }
-
-  unsigned int hashValue = hash_string(name, len);
+  if (use_alternate_hashcode()) {
+    hashValue = alt_hash_string(name, len);
+  }
   int index = the_table()->hash_to_index(hashValue);
   found_string = the_table()->lookup_in_main_table(index, name, len, hashValue);
 
   // Found
   if (found_string != NULL) {