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Core: new blenlib library for implicit-sharing #105994

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Jacques Lucke merged 17 commits from JacquesLucke/blender:implicit-sharing into main 2023-03-28 13:58:02 +02:00
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source/blender/blenlib/BLI_implicit_sharing.hh
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@ -73,7 +73,7 @@ class ImplicitSharingInfo : NonCopyable, NonMovable {
*/
void remove_user_and_delete_if_last() const
{
const int old_user_count = users_.fetch_sub(1, std::memory_order_relaxed);
const int old_user_count = users_.fetch_sub(1, std::memory_order_acq_rel);
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Brecht Van Lommel commented 2023-03-24 13:05:34 +01:00
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My understanding is that user count decrement requires std::memory_order_acq_rel, while increment can use std::memory_order_relaxed.

For example libc++ does this for shared_ptr. More details:
https://stackoverflow.com/questions/48124031/stdmemory-order-relaxed-atomicity-with-respect-to-the-same-atomic-variable

My understanding is that user count decrement requires `std::memory_order_acq_rel`, while increment can use `std::memory_order_relaxed`. For example libc++ does this for shared_ptr. More details: https://stackoverflow.com/questions/48124031/stdmemory-order-relaxed-atomicity-with-respect-to-the-same-atomic-variable
BLI_assert(old_user_count >= 1);
const bool was_last_user = old_user_count == 1;
if (was_last_user) {