Dear List,
I've implemented a simple "Synchronous Channel" using dispatch lib.
A "synchronous channel" is an actor in which each producer offering an item
(via a put operation) must wait for a consumer to take this item (via a get
operation), and vice versa.
The following is probably the simplest implementation, which lacks some
important features like timeout etc.
But anyway, is the following a proper and *efficient* implementation when using
dispatch lib where consumers and producers will be scheduled in queues and the
semaphore is implemented using dispatch_semaphore?
Any hints to improve this?
template <typename T>
class SimpleSynchronousChannel {
public:
SimpleSynchronousChannel()
: sync_(0), send_(1), recv_(0)
{
}
void put(const T& v) {
send_.wait();
value_ = v;
recv_.signal();
sync_.wait();
}
T get() {
recv_.wait();
T result = value_;
sync_.signal();
send_.signal();
return result;
}
private:
T value_;
semaphore sync_;
semaphore send_;
semaphore recv_;
};
benchmark info: if I run concurrently one producer (performing put()) and one
consumer (performing get()), I get a throughput of about 200.000 items/sec on a
MacBookPro)
class semaphore is a simple wrapper around dispatch_semaphore:
class semaphore : noncopyable {
public:
explicit semaphore(long n) : sem_(dispatch_semaphore_create(n)) {
assert(sem_);
}
~semaphore() {
dispatch_release(sem_);
}
void signal() {
dispatch_semaphore_signal(sem_);
}
bool wait() { return dispatch_semaphore_wait(sem_,
DISPATCH_TIME_FOREVER) == 0; }
bool wait(double timeout_sec) {
long result = dispatch_semaphore_wait(sem_,
timeout_sec >= 0 ?
dispatch_time(DISPATCH_TIME_NOW, timeout_sec*1e9)
: DISPATCH_TIME_FOREVER);
return result == 0;
}
private:
dispatch_semaphore_t sem_;
};
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