8330027: Identity hashes of archived objects must be based on a reproducible random seed

Reviewed-by: ccheung, iklam

Author: tstuefe

src/hotspot/share/cds/archiveHeapWriter.cpp

@@ -530,10 +530,8 @@ void ArchiveHeapWriter::update_header_for_requested_obj(oop requested_obj, oop s
   fake_oop->set_narrow_klass(nk);
 
   // We need to retain the identity_hash, because it may have been used by some hashtables
-  // in the shared heap. This also has the side effect of pre-initializing the
-  // identity_hash for all shared objects, so they are less likely to be written
-  // into during run time, increasing the potential of memory sharing.
-  if (src_obj != nullptr) {
+  // in the shared heap.
+  if (src_obj != nullptr && !src_obj->fast_no_hash_check()) {
     intptr_t src_hash = src_obj->identity_hash();
     fake_oop->set_mark(markWord::prototype().copy_set_hash(src_hash));
     assert(fake_oop->mark().is_unlocked(), "sanity");

src/hotspot/share/cds/heapShared.cpp

@@ -278,12 +278,6 @@ bool HeapShared::archive_object(oop obj) {
   } else {
     count_allocation(obj->size());
     ArchiveHeapWriter::add_source_obj(obj);
-
-    // The archived objects are discovered in a predictable order. Compute
-    // their identity_hash() as soon as we see them. This ensures that the
-    // the identity_hash in the object header will have a predictable value,
-    // making the archive reproducible.
-    obj->identity_hash();
     CachedOopInfo info = make_cached_oop_info(obj);
     archived_object_cache()->put_when_absent(obj, info);
     archived_object_cache()->maybe_grow();

src/hotspot/share/runtime/thread.cpp

@@ -24,6 +24,7 @@
  */
 
 #include "precompiled.hpp"
+#include "cds/cdsConfig.hpp"
 #include "classfile/javaClasses.hpp"
 #include "classfile/javaThreadStatus.hpp"
 #include "gc/shared/barrierSet.hpp"
@@ -103,7 +104,10 @@ Thread::Thread() {
   _vm_error_callbacks = nullptr;
 
   // thread-specific hashCode stream generator state - Marsaglia shift-xor form
-  _hashStateX = os::random();
+  // If we are dumping, keep ihashes constant. Note that during dumping we only
+  // ever run one java thread, and no other thread should generate ihashes either,
+  // so using a constant seed should work fine.
+  _hashStateX = CDSConfig::is_dumping_static_archive() ? 0x12345678 : os::random();
   _hashStateY = 842502087;
   _hashStateZ = 0x8767;    // (int)(3579807591LL & 0xffff) ;
   _hashStateW = 273326509;