8187443: Forest Consolidation: Move files to unified layout

Reviewed-by: darcy, ihse

src/hotspot/share/classfile/stringTable.cpp

@@ -0,0 +1,766 @@
+/*
+ * 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.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "classfile/altHashing.hpp"
+#include "classfile/compactHashtable.inline.hpp"
+#include "classfile/javaClasses.inline.hpp"
+#include "classfile/stringTable.hpp"
+#include "classfile/systemDictionary.hpp"
+#include "gc/shared/collectedHeap.inline.hpp"
+#include "gc/shared/gcLocker.inline.hpp"
+#include "logging/log.hpp"
+#include "memory/allocation.inline.hpp"
+#include "memory/filemap.hpp"
+#include "memory/metaspaceShared.hpp"
+#include "memory/resourceArea.hpp"
+#include "oops/oop.inline.hpp"
+#include "runtime/atomic.hpp"
+#include "runtime/mutexLocker.hpp"
+#include "services/diagnosticCommand.hpp"
+#include "utilities/hashtable.inline.hpp"
+#include "utilities/macros.hpp"
+#if INCLUDE_ALL_GCS
+#include "gc/g1/g1CollectedHeap.hpp"
+#include "gc/g1/g1SATBCardTableModRefBS.hpp"
+#include "gc/g1/g1StringDedup.hpp"
+#endif
+
+// the number of buckets a thread claims
+const int ClaimChunkSize = 32;
+
+#ifdef ASSERT
+class StableMemoryChecker : public StackObj {
+  enum { _bufsize = wordSize*4 };
+
+  address _region;
+  jint    _size;
+  u1      _save_buf[_bufsize];
+
+  int sample(u1* save_buf) {
+    if (_size <= _bufsize) {
+      memcpy(save_buf, _region, _size);
+      return _size;
+    } else {
+      // copy head and tail
+      memcpy(&save_buf[0],          _region,                      _bufsize/2);
+      memcpy(&save_buf[_bufsize/2], _region + _size - _bufsize/2, _bufsize/2);
+      return (_bufsize/2)*2;
+    }
+  }
+
+ public:
+  StableMemoryChecker(const void* region, jint size) {
+    _region = (address) region;
+    _size   = size;
+    sample(_save_buf);
+  }
+
+  bool verify() {
+    u1 check_buf[sizeof(_save_buf)];
+    int check_size = sample(check_buf);
+    return (0 == memcmp(_save_buf, check_buf, check_size));
+  }
+
+  void set_region(const void* region) { _region = (address) region; }
+};
+#endif
+
+
+// --------------------------------------------------------------------------
+StringTable* StringTable::_the_table = NULL;
+bool StringTable::_shared_string_mapped = false;
+bool StringTable::_needs_rehashing = false;
+
+volatile int StringTable::_parallel_claimed_idx = 0;
+
+CompactHashtable<oop, char> StringTable::_shared_table;
+
+// Pick hashing algorithm
+unsigned int StringTable::hash_string(const jchar* s, int 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);
+  }
+  ResourceMark rm(THREAD);
+  // All String oops are hashed as unicode
+  int length;
+  jchar* chars = java_lang_String::as_unicode_string(string, length, THREAD);
+  if (chars != NULL) {
+    return hash_string(chars, length);
+  } else {
+    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, 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;
+  for (HashtableEntry<oop, mtSymbol>* l = bucket(index); l != NULL; l = l->next()) {
+    count++;
+    if (l->hash() == hash) {
+      if (java_lang_String::equals(l->literal(), name, len)) {
+        return l->literal();
+      }
+    }
+  }
+  // If the bucket size is too deep check if this hash code is insufficient.
+  if (count >= rehash_count && !needs_rehashing()) {
+    _needs_rehashing = check_rehash_table(count);
+  }
+  return NULL;
+}
+
+
+oop StringTable::basic_add(int index_arg, Handle string, jchar* name,
+                           int len, unsigned int hashValue_arg, TRAPS) {
+
+  assert(java_lang_String::equals(string(), name, len),
+         "string must be properly initialized");
+  // Cannot hit a safepoint in this function because the "this" pointer can move.
+  NoSafepointVerifier nsv;
+
+  // 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 = alt_hash_string(name, len);
+    index = hash_to_index(hashValue);
+  } else {
+    hashValue = hashValue_arg;
+    index = index_arg;
+  }
+
+  // Since look-up was done lock-free, we need to check if another
+  // thread beat us in the race to insert the symbol.
+
+  // No need to lookup the shared table from here since the caller (intern()) already did
+  oop test = lookup_in_main_table(index, name, len, hashValue); // calls lookup(u1*, int)
+  if (test != NULL) {
+    // Entry already added
+    return test;
+  }
+
+  HashtableEntry<oop, mtSymbol>* entry = new_entry(hashValue, string());
+  add_entry(index, entry);
+  return string();
+}
+
+
+oop StringTable::lookup(Symbol* symbol) {
+  ResourceMark rm;
+  int length;
+  jchar* chars = symbol->as_unicode(length);
+  return lookup(chars, length);
+}
+
+// Tell the GC that this string was looked up in the StringTable.
+static void ensure_string_alive(oop string) {
+  // A lookup in the StringTable could return an object that was previously
+  // considered dead. The SATB part of G1 needs to get notified about this
+  // potential resurrection, otherwise the marking might not find the object.
+#if INCLUDE_ALL_GCS
+  if (UseG1GC && string != NULL) {
+    G1SATBCardTableModRefBS::enqueue(string);
+  }
+#endif
+}
+
+oop StringTable::lookup(jchar* name, int 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;
+  }
+  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) {
+  // 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;
+  }
+  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) {
+    if (found_string != string_or_null()) {
+      ensure_string_alive(found_string);
+    }
+    return found_string;
+  }
+
+  debug_only(StableMemoryChecker smc(name, len * sizeof(name[0])));
+  assert(!Universe::heap()->is_in_reserved(name),
+         "proposed name of symbol must be stable");
+
+  HandleMark hm(THREAD);  // cleanup strings created
+  Handle string;
+  // try to reuse the string if possible
+  if (!string_or_null.is_null()) {
+    string = string_or_null;
+  } else {
+    string = java_lang_String::create_from_unicode(name, len, CHECK_NULL);
+  }
+
+#if INCLUDE_ALL_GCS
+  if (G1StringDedup::is_enabled()) {
+    // Deduplicate the string before it is interned. Note that we should never
+    // deduplicate a string after it has been interned. Doing so will counteract
+    // compiler optimizations done on e.g. interned string literals.
+    G1StringDedup::deduplicate(string());
+  }
+#endif
+
+  // Grab the StringTable_lock before getting the_table() because it could
+  // change at safepoint.
+  oop added_or_found;
+  {
+    MutexLocker ml(StringTable_lock, THREAD);
+    // Otherwise, add to symbol to table
+    added_or_found = the_table()->basic_add(index, string, name, len,
+                                  hashValue, CHECK_NULL);
+  }
+
+  if (added_or_found != string()) {
+    ensure_string_alive(added_or_found);
+  }
+
+  return added_or_found;
+}
+
+oop StringTable::intern(Symbol* symbol, TRAPS) {
+  if (symbol == NULL) return NULL;
+  ResourceMark rm(THREAD);
+  int length;
+  jchar* chars = symbol->as_unicode(length);
+  Handle string;
+  oop result = intern(string, chars, length, CHECK_NULL);
+  return result;
+}
+
+
+oop StringTable::intern(oop string, TRAPS)
+{
+  if (string == NULL) return NULL;
+  ResourceMark rm(THREAD);
+  int length;
+  Handle h_string (THREAD, string);
+  jchar* chars = java_lang_String::as_unicode_string(string, length, CHECK_NULL);
+  oop result = intern(h_string, chars, length, CHECK_NULL);
+  return result;
+}
+
+
+oop StringTable::intern(const char* utf8_string, TRAPS) {
+  if (utf8_string == NULL) return NULL;
+  ResourceMark rm(THREAD);
+  int length = UTF8::unicode_length(utf8_string);
+  jchar* chars = NEW_RESOURCE_ARRAY(jchar, length);
+  UTF8::convert_to_unicode(utf8_string, chars, length);
+  Handle string;
+  oop result = intern(string, chars, length, CHECK_NULL);
+  return result;
+}
+
+void StringTable::unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int* processed, int* removed) {
+  BucketUnlinkContext context;
+  buckets_unlink_or_oops_do(is_alive, f, 0, the_table()->table_size(), &context);
+  _the_table->bulk_free_entries(&context);
+  *processed = context._num_processed;
+  *removed = context._num_removed;
+}
+
+void StringTable::possibly_parallel_unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int* processed, int* removed) {
+  // Readers of the table are unlocked, so we should only be removing
+  // entries at a safepoint.
+  assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
+  const int limit = the_table()->table_size();
+
+  BucketUnlinkContext context;
+  for (;;) {
+    // Grab next set of buckets to scan
+    int start_idx = Atomic::add(ClaimChunkSize, &_parallel_claimed_idx) - ClaimChunkSize;
+    if (start_idx >= limit) {
+      // End of table
+      break;
+    }
+
+    int end_idx = MIN2(limit, start_idx + ClaimChunkSize);
+    buckets_unlink_or_oops_do(is_alive, f, start_idx, end_idx, &context);
+  }
+  _the_table->bulk_free_entries(&context);
+  *processed = context._num_processed;
+  *removed = context._num_removed;
+}
+
+void StringTable::buckets_oops_do(OopClosure* f, int start_idx, int end_idx) {
+  const int limit = the_table()->table_size();
+
+  assert(0 <= start_idx && start_idx <= limit,
+         "start_idx (%d) is out of bounds", start_idx);
+  assert(0 <= end_idx && end_idx <= limit,
+         "end_idx (%d) is out of bounds", end_idx);
+  assert(start_idx <= end_idx,
+         "Index ordering: start_idx=%d, end_idx=%d",
+         start_idx, end_idx);
+
+  for (int i = start_idx; i < end_idx; i += 1) {
+    HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
+    while (entry != NULL) {
+      assert(!entry->is_shared(), "CDS not used for the StringTable");
+
+      f->do_oop((oop*)entry->literal_addr());
+
+      entry = entry->next();
+    }
+  }
+}
+
+void StringTable::buckets_unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int start_idx, int end_idx, BucketUnlinkContext* context) {
+  const int limit = the_table()->table_size();
+
+  assert(0 <= start_idx && start_idx <= limit,
+         "start_idx (%d) is out of bounds", start_idx);
+  assert(0 <= end_idx && end_idx <= limit,
+         "end_idx (%d) is out of bounds", end_idx);
+  assert(start_idx <= end_idx,
+         "Index ordering: start_idx=%d, end_idx=%d",
+         start_idx, end_idx);
+
+  for (int i = start_idx; i < end_idx; ++i) {
+    HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i);
+    HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
+    while (entry != NULL) {
+      assert(!entry->is_shared(), "CDS not used for the StringTable");
+
+      if (is_alive->do_object_b(entry->literal())) {
+        if (f != NULL) {
+          f->do_oop((oop*)entry->literal_addr());
+        }
+        p = entry->next_addr();
+      } else {
+        *p = entry->next();
+        context->free_entry(entry);
+      }
+      context->_num_processed++;
+      entry = *p;
+    }
+  }
+}
+
+void StringTable::oops_do(OopClosure* f) {
+  buckets_oops_do(f, 0, the_table()->table_size());
+}
+
+void StringTable::possibly_parallel_oops_do(OopClosure* f) {
+  const int limit = the_table()->table_size();
+
+  for (;;) {
+    // Grab next set of buckets to scan
+    int start_idx = Atomic::add(ClaimChunkSize, &_parallel_claimed_idx) - ClaimChunkSize;
+    if (start_idx >= limit) {
+      // End of table
+      break;
+    }
+
+    int end_idx = MIN2(limit, start_idx + ClaimChunkSize);
+    buckets_oops_do(f, start_idx, end_idx);
+  }
+}
+
+// This verification is part of Universe::verify() and needs to be quick.
+// See StringTable::verify_and_compare() below for exhaustive verification.
+void StringTable::verify() {
+  for (int i = 0; i < the_table()->table_size(); ++i) {
+    HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);
+    for ( ; p != NULL; p = p->next()) {
+      oop s = p->literal();
+      guarantee(s != NULL, "interned string is NULL");
+      unsigned int h = hash_string(s);
+      guarantee(p->hash() == h, "broken hash in string table entry");
+      guarantee(the_table()->hash_to_index(h) == i,
+                "wrong index in string table");
+    }
+  }
+}
+
+void StringTable::dump(outputStream* st, bool verbose) {
+  if (!verbose) {
+    the_table()->print_table_statistics(st, "StringTable");
+  } else {
+    Thread* THREAD = Thread::current();
+    st->print_cr("VERSION: 1.1");
+    for (int i = 0; i < the_table()->table_size(); ++i) {
+      HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);
+      for ( ; p != NULL; p = p->next()) {
+        oop s = p->literal();
+        typeArrayOop value  = java_lang_String::value(s);
+        int          length = java_lang_String::length(s);
+        bool      is_latin1 = java_lang_String::is_latin1(s);
+
+        if (length <= 0) {
+          st->print("%d: ", length);
+        } else {
+          ResourceMark rm(THREAD);
+          int utf8_length = length;
+          char* utf8_string;
+
+          if (!is_latin1) {
+            jchar* chars = value->char_at_addr(0);
+            utf8_string = UNICODE::as_utf8(chars, utf8_length);
+          } else {
+            jbyte* bytes = value->byte_at_addr(0);
+            utf8_string = UNICODE::as_utf8(bytes, utf8_length);
+          }
+
+          st->print("%d: ", utf8_length);
+          HashtableTextDump::put_utf8(st, utf8_string, utf8_length);
+        }
+        st->cr();
+      }
+    }
+  }
+}
+
+StringTable::VerifyRetTypes StringTable::compare_entries(
+                                      int bkt1, int e_cnt1,
+                                      HashtableEntry<oop, mtSymbol>* e_ptr1,
+                                      int bkt2, int e_cnt2,
+                                      HashtableEntry<oop, mtSymbol>* e_ptr2) {
+  // These entries are sanity checked by verify_and_compare_entries()
+  // before this function is called.
+  oop str1 = e_ptr1->literal();
+  oop str2 = e_ptr2->literal();
+
+  if (str1 == str2) {
+    tty->print_cr("ERROR: identical oop values (0x" PTR_FORMAT ") "
+                  "in entry @ bucket[%d][%d] and entry @ bucket[%d][%d]",
+                  p2i(str1), bkt1, e_cnt1, bkt2, e_cnt2);
+    return _verify_fail_continue;
+  }
+
+  if (java_lang_String::equals(str1, str2)) {
+    tty->print_cr("ERROR: identical String values in entry @ "
+                  "bucket[%d][%d] and entry @ bucket[%d][%d]",
+                  bkt1, e_cnt1, bkt2, e_cnt2);
+    return _verify_fail_continue;
+  }
+
+  return _verify_pass;
+}
+
+StringTable::VerifyRetTypes StringTable::verify_entry(int bkt, int e_cnt,
+                                      HashtableEntry<oop, mtSymbol>* e_ptr,
+                                      StringTable::VerifyMesgModes mesg_mode) {
+
+  VerifyRetTypes ret = _verify_pass;  // be optimistic
+
+  oop str = e_ptr->literal();
+  if (str == NULL) {
+    if (mesg_mode == _verify_with_mesgs) {
+      tty->print_cr("ERROR: NULL oop value in entry @ bucket[%d][%d]", bkt,
+                    e_cnt);
+    }
+    // NULL oop means no more verifications are possible
+    return _verify_fail_done;
+  }
+
+  if (str->klass() != SystemDictionary::String_klass()) {
+    if (mesg_mode == _verify_with_mesgs) {
+      tty->print_cr("ERROR: oop is not a String in entry @ bucket[%d][%d]",
+                    bkt, e_cnt);
+    }
+    // not a String means no more verifications are possible
+    return _verify_fail_done;
+  }
+
+  unsigned int h = hash_string(str);
+  if (e_ptr->hash() != h) {
+    if (mesg_mode == _verify_with_mesgs) {
+      tty->print_cr("ERROR: broken hash value in entry @ bucket[%d][%d], "
+                    "bkt_hash=%d, str_hash=%d", bkt, e_cnt, e_ptr->hash(), h);
+    }
+    ret = _verify_fail_continue;
+  }
+
+  if (the_table()->hash_to_index(h) != bkt) {
+    if (mesg_mode == _verify_with_mesgs) {
+      tty->print_cr("ERROR: wrong index value for entry @ bucket[%d][%d], "
+                    "str_hash=%d, hash_to_index=%d", bkt, e_cnt, h,
+                    the_table()->hash_to_index(h));
+    }
+    ret = _verify_fail_continue;
+  }
+
+  return ret;
+}
+
+// See StringTable::verify() above for the quick verification that is
+// part of Universe::verify(). This verification is exhaustive and
+// reports on every issue that is found. StringTable::verify() only
+// reports on the first issue that is found.
+//
+// StringTable::verify_entry() checks:
+// - oop value != NULL (same as verify())
+// - oop value is a String
+// - hash(String) == hash in entry (same as verify())
+// - index for hash == index of entry (same as verify())
+//
+// StringTable::compare_entries() checks:
+// - oops are unique across all entries
+// - String values are unique across all entries
+//
+int StringTable::verify_and_compare_entries() {
+  assert(StringTable_lock->is_locked(), "sanity check");
+
+  int  fail_cnt = 0;
+
+  // first, verify all the entries individually:
+  for (int bkt = 0; bkt < the_table()->table_size(); bkt++) {
+    HashtableEntry<oop, mtSymbol>* e_ptr = the_table()->bucket(bkt);
+    for (int e_cnt = 0; e_ptr != NULL; e_ptr = e_ptr->next(), e_cnt++) {
+      VerifyRetTypes ret = verify_entry(bkt, e_cnt, e_ptr, _verify_with_mesgs);
+      if (ret != _verify_pass) {
+        fail_cnt++;
+      }
+    }
+  }
+
+  // Optimization: if the above check did not find any failures, then
+  // the comparison loop below does not need to call verify_entry()
+  // before calling compare_entries(). If there were failures, then we
+  // have to call verify_entry() to see if the entry can be passed to
+  // compare_entries() safely. When we call verify_entry() in the loop
+  // below, we do so quietly to void duplicate messages and we don't
+  // increment fail_cnt because the failures have already been counted.
+  bool need_entry_verify = (fail_cnt != 0);
+
+  // second, verify all entries relative to each other:
+  for (int bkt1 = 0; bkt1 < the_table()->table_size(); bkt1++) {
+    HashtableEntry<oop, mtSymbol>* e_ptr1 = the_table()->bucket(bkt1);
+    for (int e_cnt1 = 0; e_ptr1 != NULL; e_ptr1 = e_ptr1->next(), e_cnt1++) {
+      if (need_entry_verify) {
+        VerifyRetTypes ret = verify_entry(bkt1, e_cnt1, e_ptr1,
+                                          _verify_quietly);
+        if (ret == _verify_fail_done) {
+          // cannot use the current entry to compare against other entries
+          continue;
+        }
+      }
+
+      for (int bkt2 = bkt1; bkt2 < the_table()->table_size(); bkt2++) {
+        HashtableEntry<oop, mtSymbol>* e_ptr2 = the_table()->bucket(bkt2);
+        int e_cnt2;
+        for (e_cnt2 = 0; e_ptr2 != NULL; e_ptr2 = e_ptr2->next(), e_cnt2++) {
+          if (bkt1 == bkt2 && e_cnt2 <= e_cnt1) {
+            // skip the entries up to and including the one that
+            // we're comparing against
+            continue;
+          }
+
+          if (need_entry_verify) {
+            VerifyRetTypes ret = verify_entry(bkt2, e_cnt2, e_ptr2,
+                                              _verify_quietly);
+            if (ret == _verify_fail_done) {
+              // cannot compare against this entry
+              continue;
+            }
+          }
+
+          // compare two entries, report and count any failures:
+          if (compare_entries(bkt1, e_cnt1, e_ptr1, bkt2, e_cnt2, e_ptr2)
+              != _verify_pass) {
+            fail_cnt++;
+          }
+        }
+      }
+    }
+  }
+  return fail_cnt;
+}
+
+// Create a new table and using alternate hash code, populate the new table
+// with the existing strings.   Set flag to use the alternate hash code afterwards.
+void StringTable::rehash_table() {
+  assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
+  // This should never happen with -Xshare:dump but it might in testing mode.
+  if (DumpSharedSpaces) return;
+  StringTable* new_table = new StringTable();
+
+  // Rehash the table
+  the_table()->move_to(new_table);
+
+  // Delete the table and buckets (entries are reused in new table).
+  delete _the_table;
+  // Don't check if we need rehashing until the table gets unbalanced again.
+  // Then rehash with a new global seed.
+  _needs_rehashing = false;
+  _the_table = new_table;
+}
+
+// Utility for dumping strings
+StringtableDCmd::StringtableDCmd(outputStream* output, bool heap) :
+                                 DCmdWithParser(output, heap),
+  _verbose("-verbose", "Dump the content of each string in the table",
+           "BOOLEAN", false, "false") {
+  _dcmdparser.add_dcmd_option(&_verbose);
+}
+
+void StringtableDCmd::execute(DCmdSource source, TRAPS) {
+  VM_DumpHashtable dumper(output(), VM_DumpHashtable::DumpStrings,
+                         _verbose.value());
+  VMThread::execute(&dumper);
+}
+
+int StringtableDCmd::num_arguments() {
+  ResourceMark rm;
+  StringtableDCmd* dcmd = new StringtableDCmd(NULL, false);
+  if (dcmd != NULL) {
+    DCmdMark mark(dcmd);
+    return dcmd->_dcmdparser.num_arguments();
+  } else {
+    return 0;
+  }
+}
+
+#if INCLUDE_CDS_JAVA_HEAP
+// Sharing
+oop StringTable::create_archived_string(oop s, Thread* THREAD) {
+  assert(DumpSharedSpaces, "this function is only used with -Xshare:dump");
+
+  oop new_s = NULL;
+  typeArrayOop v = java_lang_String::value(s);
+  typeArrayOop new_v = (typeArrayOop)MetaspaceShared::archive_heap_object(v, THREAD);
+  if (new_v == NULL) {
+    return NULL;
+  }
+  new_s = MetaspaceShared::archive_heap_object(s, THREAD);
+  if (new_s == NULL) {
+    return NULL;
+  }
+
+  // adjust the pointer to the 'value' field in the new String oop
+  java_lang_String::set_value_raw(new_s, new_v);
+  return new_s;
+}
+
+bool StringTable::copy_shared_string(GrowableArray<MemRegion> *string_space,
+                                     CompactStringTableWriter* writer) {
+  assert(MetaspaceShared::is_heap_object_archiving_allowed(), "must be");
+
+  Thread* THREAD = Thread::current();
+  G1CollectedHeap::heap()->begin_archive_alloc_range();
+  for (int i = 0; i < the_table()->table_size(); ++i) {
+    HashtableEntry<oop, mtSymbol>* bucket = the_table()->bucket(i);
+    for ( ; bucket != NULL; bucket = bucket->next()) {
+      oop s = bucket->literal();
+      unsigned int hash = java_lang_String::hash_code(s);
+      if (hash == 0) {
+        continue;
+      }
+
+      java_lang_String::set_hash(s, hash);
+      oop new_s = create_archived_string(s, THREAD);
+      if (new_s == NULL) {
+        continue;
+      }
+
+      // set the archived string in bucket
+      bucket->set_literal(new_s);
+
+      // add to the compact table
+      writer->add(hash, new_s);
+    }
+  }
+
+  G1CollectedHeap::heap()->end_archive_alloc_range(string_space, os::vm_allocation_granularity());
+  return true;
+}
+
+void StringTable::write_to_archive(GrowableArray<MemRegion> *string_space) {
+  assert(MetaspaceShared::is_heap_object_archiving_allowed(), "must be");
+
+  _shared_table.reset();
+  int num_buckets = the_table()->number_of_entries() /
+                         SharedSymbolTableBucketSize;
+  // calculation of num_buckets can result in zero buckets, we need at least one
+  CompactStringTableWriter writer(num_buckets > 1 ? num_buckets : 1,
+                                  &MetaspaceShared::stats()->string);
+
+  // Copy the interned strings into the "string space" within the java heap
+  if (copy_shared_string(string_space, &writer)) {
+    writer.dump(&_shared_table);
+  }
+}
+
+void StringTable::serialize(SerializeClosure* soc) {
+  _shared_table.set_type(CompactHashtable<oop, char>::_string_table);
+  _shared_table.serialize(soc);
+
+  if (soc->writing()) {
+    _shared_table.reset(); // Sanity. Make sure we don't use the shared table at dump time
+  } else if (!_shared_string_mapped) {
+    _shared_table.reset();
+  }
+}
+
+void StringTable::shared_oops_do(OopClosure* f) {
+  _shared_table.oops_do(f);
+}
+#endif //INCLUDE_CDS_JAVA_HEAP
+