Load-link/store-conditional

In computer science, load-linked/store-conditional (LL/SC), sometimes known as load-reserved/store-conditional (LR/SC), are a pair of instructions used in multithreading to achieve synchronization. Load-link returns the current value of a memory location, while a subsequent store-conditional to the same memory location will store a new value only if no updates have occurred to that location since the load-link. Together, this implements a lock-free, atomic, read-modify-write operation.

"Load-linked" is also known as load-link, load-reserved, and load-locked.

LL/SC was originally proposed by Jensen, Hagensen, and Broughton for the S-1 AAP multiprocessor at Lawrence Livermore National Laboratory.