vspace::SyncVar< T > Class Template Reference

#include <vspace.h>

Public Member Functions
	SyncVar ()
T	read ()
Result< T >	try_read ()
bool	write (T value)
bool	test ()

Private Member Functions
bool	start_wait (internals::ipc_signal_t sig)
void	stop_wait ()

Private Attributes
FastLock	_lock
VRef< Semaphore >	_sem
bool	_set
T	_value

Friends
template<typename U >
class	SyncReadEvent

Detailed Description

template<typename T>
class vspace::SyncVar< T >

Definition at line 2469 of file vspace.h.

Constructor & Destructor Documentation

SyncVar()

template<typename T >

vspace::SyncVar< T >::SyncVar ( )

inline

Definition at line 2480 of file vspace.h.

: _set(false) { }

Member Function Documentation

read()

template<typename T >

T vspace::SyncVar< T >::read

Definition at line 2517 of file vspace.h.

                   {
  _lock.lock();
  if (_set) {
    _lock.unlock();
    return _value;
  }
  if (_sem.is_null()) {
    _sem = vnew<Semaphore>();
  }
  // We can't wait inside the lock without deadlocking; but waiting outside
  // could cause a race condition with _sem being freed due to being idle.
  // Thus, we use start_wait() to insert ourselves into the queue, then
  // use wait_signal() outside the lock to complete waiting.
  //
  // Note: start_wait() will not send a signal to self, as _set is
  // false and therefore _sem->value() must be zero.
  _sem->start_wait(0);
  _lock.unlock();
  internals::wait_signal();
  _lock.lock();
  if (_sem->_idle())
    _sem->post();
  else {
    _sem.free();
    _sem = vnull<Semaphore>();
  }
  _lock.unlock();
  return _value;
}

start_wait()

template<typename T >

bool vspace::SyncVar< T >::start_wait ( internals::ipc_signal_t  sig )

private

Definition at line 2490 of file vspace.h.

                                                     {
  _lock.lock();
  if (_set) {
    internals::send_signal(internals::vmem.current_process, sig);
    _lock.unlock();
    return true;
  }
  if (_sem.is_null()) {
    _sem = vnew<Semaphore>();
  }
  bool result = _sem->start_wait(sig);
  _lock.unlock();
  return result;
}

stop_wait()

template<typename T >

void vspace::SyncVar< T >::stop_wait

private

Definition at line 2506 of file vspace.h.

                           {
  _lock.lock();
  if (!_sem.is_null()) {
    _sem->stop_wait();
    if (!_sem->_idle())
      _sem->post();
  }
  _lock.unlock();
}

test()

template<typename T >

bool vspace::SyncVar< T >::test ( )

inline

Definition at line 2484 of file vspace.h.

              {
    return _set;
  }

try_read()

template<typename T >

Result< T > vspace::SyncVar< T >::try_read

Definition at line 2548 of file vspace.h.

                               {
  _lock.lock();
  Result<T> result = _set ? Result<T>(_value) : Result<T>();
  _lock.unlock();
  return result;
}

write()

template<typename T >

bool vspace::SyncVar< T >::write

(

T

value

)

Definition at line 2556 of file vspace.h.

                              {
  _lock.lock();
  if (_set) {
    _lock.unlock();
    return false;
  }
  _set = true;
  _value = value;
  if (!_sem->_idle())
    _sem->post();
  _lock.unlock();
  return true;
}

Friends And Related Function Documentation

SyncReadEvent

template<typename T >

template<typename U >

friend class SyncReadEvent

friend

Definition at line 2476 of file vspace.h.

Field Documentation

_lock

template<typename T >

FastLock vspace::SyncVar< T >::_lock

private

Definition at line 2471 of file vspace.h.

_sem

template<typename T >

VRef<Semaphore> vspace::SyncVar< T >::_sem

private

Definition at line 2472 of file vspace.h.

_set

template<typename T >

bool vspace::SyncVar< T >::_set

private

Definition at line 2473 of file vspace.h.

_value

template<typename T >

T vspace::SyncVar< T >::_value

private

Definition at line 2474 of file vspace.h.

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The documentation for this class was generated from the following file:

• kernel/oswrapper/vspace.h