Guarded Suspension applies a unique strategy to deal with mutation. It signals when it is done with its modification.

Dealing with Mutation: Guarded Suspension

by Rainer Grimm

From the article:

The guarded suspension basic variant combines a lock and a precondition that must be satisfied. If the precondition is not fulfilled, that checking thread puts itself to sleep. The checking thread uses a lock to avoid a race condition that may result in a data race or a deadlock.

Various variants of the Guarded Suspension exist:

• The waiting thread can passively be notified about the state change or actively ask for the state change. In short, I call this push versus pull principle.
• The waiting can be done with or without a time boundary.
• The notification can be sent to one or all waiting threads.

I present in this post only the rough idea. Let me start with the push principle.

You often synchronize threads with a condition variable or a future/promise pair. The condition variable or the promise sends the notification to the waiting thread. A promise has no notify_one or notify_all member function. Typically, a valueless set_value call is used to ...