Temporarily Dropping a Lock: The Anti-lock Pattern -- Raymond Chen

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In C++, it's common to use RAII types like std::lock_guard to manage synchronization primitives, ensuring a lock is acquired at object creation and released at destruction. However, a less common but useful pattern is the "anti-lock," which temporarily releases a lock and reacquires it later, useful in scenarios where you need to drop a lock while performing certain operations, like calling out to other components to avoid deadlocks.

Temporarily Dropping a Lock: The Anti-lock Pattern

by Raymond Chen

From the article:

There is a common pattern in C++ of using an RAII type to manage a synchronization primitive. There are different versions of this, but they all have the same basic pattern:

• Creating the object from a synchronization object: Locks the synchronization object.
• Destructing the object: Unlocks the synchronization object.

These types go by various names, like std::lock_guard, std::unique_lock, or std::coped_lock, and specific libraries may have versions for their own types, such as C++/WinRT’s winrt::slim_lock_guard and WIL’s wil::rwlock_release_exclusive_scope_exit (which you thankfully never actually write out; just use auto).

One thing that is missing from most standard libraries, however, is the anti-lock.

The idea of the anti-lock is that it counteracts an active lock.

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