std::scoped...:scoped_lock(3)

💖 std::scoped_lock::scoped_lock — NAME energy ✨

okay so bestie, this page lives in the C++ Standard Libary manual, section std::scoped...:scoped_lock(3), and it's literally all about the constructors of std::scoped_lock::scoped_lock. yes the NAME is the same thing twice, that's just how these pages roll, it's giving "tell me you're a constructor without telling me you're a constructor" 💅

🌸 Synopsis 🌸

explicit scoped_lock( MutexTypes&... m );           (1) (since C++17)
scoped_lock( std::adopt_lock_t, MutexTypes&... m ); (2) (since C++17)
scoped_lock( const scoped_lock& ) = delete;         (3) (since C++17)

So what's the whole vibe? It acquires ownership of the given mutexes m. that's the entire personality. 🫶

Here's the breakdown, no cap:

• (1) — the normal one. If sizeof...(MutexTypes) == 0, it literally does nothing (iconic minimalism, honestly). Otherwise, if sizeof...(MutexTypes) == 1, it effectively calls m.lock(). Otherwise — like when you've got a whole friend group of mutexes — it effectively calls std::lock(m...). group-chat lock acquisition, slay. 🔥
• (2) — the adopt_lock_t one. It acquires ownership of the mutexes m... without attempting to lock any of them. it's taking your word for it. it's not checking. 🙈

⚠️ big warning bestie: for (2), the behavior is undefined unless the current thread holds a non-shared lock (i.e., a lock acquired by lock, try_lock, try_lock_for, or try_lock_until) on each object in m.... every single one. don't be out here adopting locks you don't actually hold, that's a one-way ticket to undefined-behavior town 💀

• (3) — the copy constructor is deleted. not available. gone. you cannot copy a scoped_lock, periodt. 🚫

⚠️ also, the behavior is undefined if m is destroyed before the scoped_lock object is. the mutexes have to outlive the lock. that's the rule, bestie. the scoped_lock is the main character, but the mutexes gotta stay on stage the whole show. 👑

🎀 Parameters 🎀

• m — mutexes to acquire ownership of. the whole squad. the more the merrier (well, up to whatever MutexTypes says). 🦋

💜 Exceptions 💜

• (1) — Throws any exceptions thrown by m.lock(). if locking throws, this throws. sharing is caring. 😭
• (2) — Throws nothing. absolutely nothing. cool, calm, collected, zero drama. ✨

🧚 Defect reports 🧚

so this is the "glow-up receipts" section. the following behavior-changing defect reports were applied retroactively to previously published C++ standards (yes, they went back and fixed history, lowkey iconic):

• DR: P0739R0
• Applied to: C++17
• Behavior as published: the adopt_lock_t parameter was last, impeding class template argument deduction
• Correct behavior: moved to first

basically the adopt_lock_t was sitting at the back of the bus and it was messing with class template argument deduction, so they moved it to the front. glow-up complete. 💅⭐

and that's the page bestie, from http://cppreference.com 🌈 — version date 2024.06.10 — go forth and lock responsibly 💖🎀🦋🍓