A ReadMostlyAtomicObserver guarantees that reading is exactly one relaxed atomic load and a read from a thread local bool. Like AtomicObserver, the value is cached using std::atomic. However, there is no version check when reading which means that the cached value may be out-of-date with the Observer value. The cached value will be updated asynchronously in a background thread.
Declared in <folly/observer/Observer.h>
template<typename T>
class ReadMostlyAtomicObserver;When get() is called from makeObserver, the underlying observer is directly snapshotted to ensure dependent observers have current values and capture dependencies.
ReadMostlyAtomicObserver is ideal for fastest possible reads on a trivially-copyable type when a slightly out-of-date value will suffice. It is perfect for very frequent reads coupled with very infrequent writes.
Observer<int> observer = ...; ReadMostlyAtomicObserver<int> atomicObserver(observer); auto value = *atomicObserver;
| Name | Description |
|---|---|
ReadMostlyAtomicObserver [constructor] | Constructors |
operator= [deleted] | Deleted copy assignment operator. |
get | Returns the cached value. |
getUnderlyingObserver | Returns the underlying Observer. |
operator* | Returns the cached value. |
| Name | Description |
|---|---|
makeReadMostlyAtomicObserver | Same as makeObserver(...), but creates ReadMostlyAtomicObserver. |