Coverity

There have been 61 missing_lock coverity errors, most around SharedPromise usage.

In SERVER-119208, Coverity is describing a pattern of fulfilling a SharedFuture while holding an exclusive lock, but retrieving a SharedFuture without holding a lock.

• On write (ensureFulfilledPromise) in _onCoordinatorStateAdvanced, a lock is held on _mutex.
• On read, _allRecipientsDoneCloning.getFuture() is not protected by _mutex.

SharedPromise

Per the SharedPromise class documentation:

Any number of threads can extract a future at the same time. It is also safe to extract a future concurrently with completing the promise.

This was confirmed in a thread in #server-programmability.

Basically, get() and getFuture() are safe, the reads and writes to promise or future themselves may need external synchronization.

Proposal

To standardize our SharedPromise usage, all occurrences that lock on a getFuture call should be changed to remove the lock_guard.

To prevent future Coverity issues, a Coverity suppression should be added for all getFuture usages.