Re: code pattern for locking & unlocking
On 25/11/10 22:48, Daniel Anderson wrote:
I often have to acquire locks and release them after I'm finished with
them.
I use constructor/destructor to acquire& release locks. everything
works fine.
sometime I must acquire a lock for few instructions, then release it
in the middle of a big function. I use braces to get timely
destructors, but I find the "middle of nowhere" braces kind of
embarrassing.
something like:
struct Lock
{
Lock(Mutex& mtx) mtx_(mtx) { mtx.lock(); }
~Lock() { mtx_.unlock(); }
operator bool() { return true;}
};
void someFunc()
{
// do some stuff
...
// now time to update share data
{
Lock myLock(data_mutex);
//use locked data
....
} // destructor called
// do more stuff
...
}
I would like to have something like the using keyword in c#.
Is there a way to fake it in C++ ?
The alternative to creating a scope just to unlock the mutex at a
particlular point, it may be simpler to provide unlock() function on the
lock, e.g.:
struct Lock
{
Mutex* mtx_;
Lock(Mutex& mtx) : mtx_(&mtx) { mtx_->lock(); }
~Lock() { this->unlock(); }
void unlock() {
if(mtx_) {
mtx_->unlock();
mtx_ = 0;
}
}
};
void someFunc()
{
Lock myLock(data_mutex);
// ... use locked data ...
myLock.unlock(); // unlock long before leaving the scope
// ... more code ...
}
Notice in the above how no artificial scope is introduced and
myLock.unlock() does exactly what it says.
for now I'm using an if to do it.
void someFunc()
{
// do some stuff
...
// now time to update share data
if (Lock myLock = Lock(data_mutex))
{
//use locked data
....
} // Unlock done by destructor
// do more stuff
...
}
Is it good programming ?
If statement naturally means it is conditional, so that a reader of such
code may be led to think that obtaining the lock may fail and the
control flow may skip the block guarded by if.
--
Max
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