Add ThreadBarrier; use in GCMarker and unit test

runtime/vm/random.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/random.h"
 #include "vm/flags.h"
 #include "vm/isolate.h"
 
 namespace dart {
 
 DEFINE_FLAG(int, random_seed, 0, "Override the random seed for debugging.");
 
 Random::Random() {
   uint64_t seed = FLAG_random_seed;
   if (seed == 0) {
     Dart_EntropySource callback = Isolate::entropy_source_callback();
     if (callback != NULL) {
       if (!callback(reinterpret_cast<uint8_t*>(&seed), sizeof(seed))) {
         // Callback failed. Reset the seed to 0.
         seed = 0;
       }
     }
   }
   if (seed == 0) {
     // We did not get a seed so far. As a fallback we do use the current time.
     seed = OS::GetCurrentTimeMicros();
   }
+  Initialize(seed);
+}
+
+
+void Random::Initialize(uint64_t seed) {
+  ASSERT(seed != 0);
   // Crank the next state a couple of times.
   _state = seed;
   NextState();
   NextState();
   NextState();
   NextState();
 }
 
+
+Random::Random(uint64_t seed) {
+  Initialize(seed);
+}
+
+
 Random::~Random() {
   // Nothing to be done here.
 }
 
 // The algorithm used here is Multiply with Carry (MWC) with a Base b = 2^32.
 // http://en.wikipedia.org/wiki/Multiply-with-carry
 // The constant A is selected from "Numerical Recipes 3rd Edition" p.348 B1.
 void Random::NextState() {
   const uint64_t MASK_32 = 0xffffffff;
   const uint64_t A = 0xffffda61;
 
   uint64_t state_lo = _state & MASK_32;
   uint64_t state_hi = (_state >> 32) & MASK_32;
   _state = (A * state_lo) + state_hi;
 }
 
 
 uint32_t Random::NextUInt32() {
   const uint64_t MASK_32 = 0xffffffff;
   NextState();
   return static_cast<uint32_t>(_state & MASK_32);
 }
 
 }  // namespace dart