Turn off parallel and concurrent sweeping on system with just one processor/core.

src/isolate.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 118 matching lines @@
 v8::TryCatch* ThreadLocalTop::TryCatchHandler() {
   return TRY_CATCH_FROM_ADDRESS(try_catch_handler_address());
 }
 
 
 int SystemThreadManager::NumberOfParallelSystemThreads(
     ParallelSystemComponent type) {
   int number_of_threads = Min(OS::NumberOfCores(), kMaxThreads);
   ASSERT(number_of_threads > 0);
   if (number_of_threads ==  1) {
-    return 1;
+    return 0;
   }
   if (type == PARALLEL_SWEEPING) {
     return number_of_threads;
   } else if (type == CONCURRENT_SWEEPING) {
     return number_of_threads - 1;
   } else if (type == PARALLEL_MARKING) {
     return number_of_threads;
   }
   return 1;
 }
@@ skipping 2016 matching lines @@
     FLAG_marking_threads = SystemThreadManager::
         NumberOfParallelSystemThreads(
             SystemThreadManager::PARALLEL_MARKING);
   }
   if (FLAG_marking_threads > 0) {
     marking_thread_ = new MarkingThread*[FLAG_marking_threads];
     for (int i = 0; i < FLAG_marking_threads; i++) {
       marking_thread_[i] = new MarkingThread(this);
       marking_thread_[i]->Start();
     }
+  } else {
+    FLAG_parallel_marking = false;
   }
 
   if (FLAG_sweeper_threads == 0) {
     if (FLAG_concurrent_sweeping) {
       FLAG_sweeper_threads = SystemThreadManager::
           NumberOfParallelSystemThreads(
               SystemThreadManager::CONCURRENT_SWEEPING);
     } else if (FLAG_parallel_sweeping) {
       FLAG_sweeper_threads = SystemThreadManager::
           NumberOfParallelSystemThreads(
               SystemThreadManager::PARALLEL_SWEEPING);
     }
   }
   if (FLAG_sweeper_threads > 0) {
     sweeper_thread_ = new SweeperThread*[FLAG_sweeper_threads];
     for (int i = 0; i < FLAG_sweeper_threads; i++) {
       sweeper_thread_[i] = new SweeperThread(this);
       sweeper_thread_[i]->Start();
     }
+  } else {
+    FLAG_concurrent_sweeping = false;
+    FLAG_parallel_sweeping = false;
   }
   return true;
 }
 
 
 // Initialized lazily to allow early
 // v8::V8::SetAddHistogramSampleFunction calls.
 StatsTable* Isolate::stats_table() {
   if (stats_table_ == NULL) {
     stats_table_ = new StatsTable;
@@ skipping 109 matching lines @@
 
 #ifdef DEBUG
 #define ISOLATE_FIELD_OFFSET(type, name, ignored)                       \
 const intptr_t Isolate::name##_debug_offset_ = OFFSET_OF(Isolate, name##_);
 ISOLATE_INIT_LIST(ISOLATE_FIELD_OFFSET)
 ISOLATE_INIT_ARRAY_LIST(ISOLATE_FIELD_OFFSET)
 #undef ISOLATE_FIELD_OFFSET
 #endif
 
 } }  // namespace v8::internal