inline void robust_spin_mutex<Mutex>::consistent()
{
//This function supposes the previous state was "fixing"
//and the current process holds the mutex
if(atomic_read32(&this->state) != fixing_state &&
atomic_read32(&this->owner) != (boost::uint32_t)get_current_process_id()){
throw interprocess_exception(lock_error, "Broken id");
}
//If that's the case, just update mutex state
atomic_write32(&this->state, correct_state);
}
inline void robust_spin_mutex<Mutex>::unlock()
{
//If in "fixing" state, unlock and mark the mutex as unrecoverable
//so next locks will fail and all threads will be notified that the
//data protected by the mutex was not recoverable.
if(atomic_read32(&this->state) == fixing_state){
atomic_write32(&this->state, broken_state);
}
//Write an invalid owner to minimize pid reuse possibility
atomic_write32(&this->owner, get_invalid_process_id());
mtx.unlock();
}
inline bool robust_spin_mutex<Mutex>::check_if_owner_dead_and_take_ownership_atomically()
{
boost::uint32_t cur_owner = get_current_process_id();
boost::uint32_t old_owner = atomic_read32(&this->owner), old_owner2;
//The cas loop guarantees that only one thread from this or another process
//will succeed taking ownership
do{
//Check if owner is dead
if(!this->is_owner_dead(old_owner)){
return false;
}
//If it's dead, try to mark this process as the owner in the owner field
old_owner2 = old_owner;
old_owner = atomic_cas32(&this->owner, cur_owner, old_owner);
}while(old_owner2 != old_owner);
//If success, we fix mutex internals to assure our ownership
mutex_traits_t::take_ownership(mtx);
return true;
}
inline void robust_spin_mutex<Mutex>::lock()
{
//If the mutex is broken (recovery didn't call consistent()),
//then throw an exception
if(atomic_read32(&this->state) == broken_state){
throw interprocess_exception(lock_error, "Broken id");
}
//This function provokes intermodule_singleton instantiation
if(!this->lock_own_unique_file()){
throw interprocess_exception(lock_error, "Broken id");
}
//Now the logic. Try to lock, if successful mark the owner
//if it fails, start recovery logic
unsigned int spin_count = 0;
while(1){
if (mtx.try_lock()){
atomic_write32(&this->owner, get_current_process_id());
break;
}
else{
//Do the dead owner checking each spin_threshold lock tries
ipcdetail::thread_yield();
++spin_count;
if(spin_count > spin_threshold){
//Check if owner dead and take ownership if possible
if(!this->robust_check()){
spin_count = 0;
}
else{
break;
}
}
}
}
}
inline bool robust_spin_mutex<Mutex>::try_lock()
{
//Same as lock() but without spinning
if(atomic_read32(&this->state) == broken_state){
throw interprocess_exception(lock_error, "Broken id");
}
if(!this->lock_own_unique_file()){
throw interprocess_exception(lock_error, "Broken id");
}
if (mtx.try_lock()){
atomic_write32(&this->owner, get_current_process_id());
return true;
}
else{
if(!this->robust_check()){
return false;
}
else{
return true;
}
}
}
inline bool robust_spin_mutex<Mutex>::previous_owner_dead()
{
//Notifies if a owner recovery has been performed in the last lock()
return atomic_read32(&this->state) == fixing_state;
}
DWORD atomicGetValue32(DWORD &value)
{
return atomic_read32((boost::uint32_t *)&value);
}