class BlockingRefCount

A BlockingRefCount provides a counter which can be incremented and

decremented, with an additional operation allowing threads to wait

for the count to become zero.

This can be useful in scenarios where an object is waiting for

in-flight callbacks to complete before cleaning up resources,

for example:

class MyClass {

void PerformAsyncOperation() {

// Increment the counter when we start the work, and decrement

// it when finished.

in_flight_ops_.Inc();

DoWork(..., /*completion_callback=*/[this](){

// ...

in_flight_ops_.Dec();

});

}

// Wait for all in-flight operations to terminate before

// destructing.

~MyClass() {

in_flight_ops_.WaitForZero();

}

BlockingRefCount in_flight_ops_;

}

BlockingRefCount must not be destructed while threads are waiting

on it.

Thread safe.