72   inline uint enter();
  73 
  74   // Exit a critical section for this synchronizer.
  75   // Precondition: enter_value must be the result of the corresponding
  76   // enter() for the critical section.
  77   inline void exit(uint enter_value);
  78 
  79   // Wait until all threads currently in a critical section for this
  80   // synchronizer have exited their critical section.  Threads that
  81   // enter a critical section after the synchronization has started
  82   // are not considered in the wait.
  83   // Precondition: No other thread may be synchronizing on this
  84   // synchronizer.
  85   void synchronize();
  86 
  87   // RAII class for managing enter/exit pairs.
  88   class CriticalSection;
  89 };
  90 
  91 inline uint SingleWriterSynchronizer::enter() {
  92   return Atomic::add(2u, &_enter);
  93 }
  94 
  95 inline void SingleWriterSynchronizer::exit(uint enter_value) {
  96   uint exit_value = Atomic::add(2u, &_exit[enter_value & 1]);
  97   // If this exit completes a synchronize request, wakeup possibly
  98   // waiting synchronizer.  Read of _waiting_for must follow the _exit
  99   // update.
 100   if (exit_value == _waiting_for) {
 101     _wakeup.signal();
 102   }
 103 }
 104 
 105 class SingleWriterSynchronizer::CriticalSection : public StackObj {
 106   SingleWriterSynchronizer* _synchronizer;
 107   uint _enter_value;
 108 
 109 public:
 110   // Enter synchronizer's critical section.
 111   explicit CriticalSection(SingleWriterSynchronizer* synchronizer) :
 112     _synchronizer(synchronizer),
 113     _enter_value(synchronizer->enter())
 114   {}
 115 
 116   // Exit synchronizer's critical section.

  72   inline uint enter();
  73 
  74   // Exit a critical section for this synchronizer.
  75   // Precondition: enter_value must be the result of the corresponding
  76   // enter() for the critical section.
  77   inline void exit(uint enter_value);
  78 
  79   // Wait until all threads currently in a critical section for this
  80   // synchronizer have exited their critical section.  Threads that
  81   // enter a critical section after the synchronization has started
  82   // are not considered in the wait.
  83   // Precondition: No other thread may be synchronizing on this
  84   // synchronizer.
  85   void synchronize();
  86 
  87   // RAII class for managing enter/exit pairs.
  88   class CriticalSection;
  89 };
  90 
  91 inline uint SingleWriterSynchronizer::enter() {
  92   return Atomic::add(&_enter, 2u);
  93 }
  94 
  95 inline void SingleWriterSynchronizer::exit(uint enter_value) {
  96   uint exit_value = Atomic::add(&_exit[enter_value & 1], 2u);
  97   // If this exit completes a synchronize request, wakeup possibly
  98   // waiting synchronizer.  Read of _waiting_for must follow the _exit
  99   // update.
 100   if (exit_value == _waiting_for) {
 101     _wakeup.signal();
 102   }
 103 }
 104 
 105 class SingleWriterSynchronizer::CriticalSection : public StackObj {
 106   SingleWriterSynchronizer* _synchronizer;
 107   uint _enter_value;
 108 
 109 public:
 110   // Enter synchronizer's critical section.
 111   explicit CriticalSection(SingleWriterSynchronizer* synchronizer) :
 112     _synchronizer(synchronizer),
 113     _enter_value(synchronizer->enter())
 114   {}
 115 
 116   // Exit synchronizer's critical section.