src/share/vm/classfile/symbolTable.cpp

rev 4735 : 8015237: Parallelize string table scanning during strong root processing
Summary: Parallelize the scanning of the intern string table by having each GC worker claim a given number of buckets.
Reviewed-by:

*** 596,605 ****
--- 596,607 ----
  // --------------------------------------------------------------------------
  StringTable* StringTable::_the_table = NULL;
  
  bool StringTable::_needs_rehashing = false;
  
+ volatile uint StringTable::_par_claimed_idx = 0;
+ 
  // Pick hashing algorithm
  unsigned int StringTable::hash_string(const jchar* s, int len) {
    return use_alternate_hashcode() ? AltHashing::murmur3_32(seed(), s, len) :
                                      java_lang_String::hash_code(s, len);
  }
*** 782,791 ****
--- 784,830 ----
        entry = (HashtableEntry<oop, mtSymbol>*)HashtableEntry<oop, mtSymbol>::make_ptr(*p);
      }
    }
  }
  
+ void StringTable::possibly_parallel_oops_do(OopClosure* f, uint worker_id) {
+   const uint ClaimChunkSize = 20;
+   const uint limit = the_table()->table_size();
+ 
+   for (;;) {
+     // Grab next set of buckets to scan
+     uint start_idx = (uint) Atomic::add((jint)ClaimChunkSize,
+                                         (volatile jint*)&_par_claimed_idx) - ClaimChunkSize;
+     if (start_idx >= limit) {
+       // End of table
+       break;
+     }
+ 
+     uint end_idx = MIN2(limit, start_idx + ClaimChunkSize);
+     //gclog_or_tty->print_cr("[%u] Claimed [%d, %d)", worker_id, start_idx, end_idx);
+ 
+     for (uint i = start_idx; i < end_idx; i += 1) {
+       HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i);
+       HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
+ 
+       while (entry != NULL) {
+         f->do_oop((oop*)entry->literal_addr());
+ 
+         // Did the closure remove the literal from the table?
+         if (entry->literal() == NULL) {
+           assert(!entry->is_shared(), "immutable hashtable entry?");
+           *p = entry->next();
+           the_table()->free_entry(entry);
+         } else {
+           p = entry->next_addr();
+         }
+         entry = (HashtableEntry<oop, mtSymbol>*)HashtableEntry<oop, mtSymbol>::make_ptr(*p);
+       }
+     }
+   }
+ }
+ 
  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();