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Contemplating std::lock_guard vs. std::scoped_lock
C 17 marked the introduction of a novel lock class, std::scoped_lock, which shares similarities with the venerable std::lock_guard. This article delves into the distinctions between these two locking mechanisms, guiding you in choosing the optimal tool for your specific needs.
When to Utilize std::lock_guard
For scenarios where you require the locking of a single mutex for the entirety of a scope, std::lock_guard offers a safer API than std::scoped_lock. Consider the following example:
{ std::scoped_lock lock; // protect this block ... }
This snippet inadvertently results in a runtime error because it engages in "invisible behavior." It appears to compile smoothly but ultimately effects no locking. The intended functionality likely required:
{ std::scoped_lock lock{mut}; // protect this block ... }
Clarifying the target mutex for locking resolves this issue. Conversely, employing std::lock_guard would prevent the first example from compiling, rendering it a clear compile-time error.
When to Utilize std::scoped_lock
When confronted with situations where multiple mutexes need locking, std::scoped_lock shines. For instance:
{ std::scoped_lock(lock1, lock2); // protect this block ... }
This snippet succinctly locks two mutexes for the duration of the block.
Conclusion
Both std::lock_guard and std::scoped_lock cater to distinct scenarios:
While std::scoped_lock provides more comprehensive functionality, std::lock_guard offers enhanced API safety in specific cases. Consider the requirements of your code carefully when selecting the most appropriate approach.
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