On 10/15/15 11:50 AM, Jonathan M Davis wrote:
On Thursday, 15 October 2015 at 15:16:59 UTC, Steven Schveighoffer wrote:
I don't really understand all the disdain for synchronized here...
Because it's usually either the wrong solution or just unnecessary. If
you are going to have a single mutex for an entire object, then it's
nice in the way that it's nice that invariants are nice. They're not at
all necessary, because the same thing can be done manually via
assertions inside of all of the public member functions, but it does
make them less error-prone.
I'm speaking just about the synchronized(mutex) statement, not about
synchronized classes or methods.
I don't think I've ever used a synchronized class.
As for synchronized statements/blocks, they're simply syntactic sugar
that add no real value that I can see, and they can do less then the
equivalent with guards/autolocks. These two pieces of code are equivalent:
synchronized(mutex)
{
}
{
Guard guard(mutex);
}
and the second one is far more flexible, since it allows for stuff like
guard.unlock() or using the mutex with a condition variable.
You can do both of these with synchronized statements, mutex.unlock
works and you can use with a condition variable.
As I said before, with the Guard lock, you have more room for error, and
visually the lock is better identified with a synchronized statement.
So,
synchronized statements are a poor-man's guard/autolock and simply not
worth having IMHO unless we find some way that it allows us to get the
compiler to do stuff (like being able to implicitly remove shared on
some level, though because you have arbitrary code within the
synchronized block and aren't dealing with encapsulated shared variables
like with synchronized classes, I don't see how we really can get the
compiler to do much special with synchronized blocks).
We could do away with new, and require people to call malloc and
constructors directly. The sugar is nice, and keeps your code from
making dumb mistakes.
I see synchronized blocks as a clear advantage over arbitrary locking
just from a cleanliness point of view.
-Steve
