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Public Member Functions | Private Member Functions | Private Attributes | Friends
vspace::SyncVar< T > Class Template Reference

#include <vspace.h>

Public Member Functions

 SyncVar ()
 
T read ()
 
Result< Ttry_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.

2480: _set(false) { }

Member Function Documentation

◆ read()

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

Definition at line 2517 of file vspace.h.

2517 {
2518 _lock.lock();
2519 if (_set) {
2520 _lock.unlock();
2521 return _value;
2522 }
2523 if (_sem.is_null()) {
2524 _sem = vnew<Semaphore>();
2525 }
2526 // We can't wait inside the lock without deadlocking; but waiting outside
2527 // could cause a race condition with _sem being freed due to being idle.
2528 // Thus, we use start_wait() to insert ourselves into the queue, then
2529 // use wait_signal() outside the lock to complete waiting.
2530 //
2531 // Note: start_wait() will not send a signal to self, as _set is
2532 // false and therefore _sem->value() must be zero.
2533 _sem->start_wait(0);
2534 _lock.unlock();
2536 _lock.lock();
2537 if (_sem->_idle())
2538 _sem->post();
2539 else {
2540 _sem.free();
2541 _sem = vnull<Semaphore>();
2542 }
2543 _lock.unlock();
2544 return _value;
2545}
VRef< Semaphore > _sem
Definition: vspace.h:2472
FastLock _lock
Definition: vspace.h:2471
ipc_signal_t wait_signal(bool lock)
Definition: vspace.cc:987

◆ 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.

2490 {
2491 _lock.lock();
2492 if (_set) {
2493 internals::send_signal(internals::vmem.current_process, sig);
2494 _lock.unlock();
2495 return true;
2496 }
2497 if (_sem.is_null()) {
2498 _sem = vnew<Semaphore>();
2499 }
2500 bool result = _sem->start_wait(sig);
2501 _lock.unlock();
2502 return result;
2503}
return result
Definition: facAbsBiFact.cc:75
static VMem & vmem
Definition: vspace.h:1635
bool send_signal(int processno, ipc_signal_t sig, bool lock)
Definition: vspace.cc:921

◆ stop_wait()

template<typename T >
void vspace::SyncVar< T >::stop_wait
private

Definition at line 2506 of file vspace.h.

2506 {
2507 _lock.lock();
2508 if (!_sem.is_null()) {
2509 _sem->stop_wait();
2510 if (!_sem->_idle())
2511 _sem->post();
2512 }
2513 _lock.unlock();
2514}

◆ test()

template<typename T >
bool vspace::SyncVar< T >::test ( )
inline

Definition at line 2484 of file vspace.h.

2484 {
2485 return _set;
2486 }

◆ try_read()

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

Definition at line 2548 of file vspace.h.

2548 {
2549 _lock.lock();
2550 Result<T> result = _set ? Result<T>(_value) : Result<T>();
2551 _lock.unlock();
2552 return result;
2553}
STATIC_VAR jList * T
Definition: janet.cc:30

◆ write()

template<typename T >
bool vspace::SyncVar< T >::write ( T  value)

Definition at line 2556 of file vspace.h.

2556 {
2557 _lock.lock();
2558 if (_set) {
2559 _lock.unlock();
2560 return false;
2561 }
2562 _set = true;
2563 _value = value;
2564 if (!_sem->_idle())
2565 _sem->post();
2566 _lock.unlock();
2567 return true;
2568}

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.


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