Pinned

In computer science, "pinned" or "pinning" generally refers to a technique or state where a resource, typically memory, is prevented from being moved or swapped by the operating system or runtime environment. This can apply to various contexts, including:

• Pinned Memory: This refers to memory that has been locked into physical RAM and cannot be swapped out to disk. This is often used in high-performance computing or applications where low latency is crucial, such as graphics processing or real-time systems. Pinning memory avoids the overhead of paging and ensures that the data is always readily accessible in RAM. However, excessive pinning can reduce the amount of memory available for other processes and may negatively impact overall system performance.

• Pinned Objects (Garbage Collection): In garbage-collected environments, objects that are "pinned" are prevented from being moved by the garbage collector. This is often necessary when an object's memory address needs to remain stable, such as when interacting with external libraries or hardware that rely on direct memory pointers. Pinning can interfere with the garbage collector's efficiency, so it should be used judiciously.

• Pinned Threads (Thread Affinity): The term can also refer to binding a thread to a specific CPU core or a set of cores. This is known as thread affinity or CPU pinning. By pinning threads, developers can reduce the overhead of thread migration between cores and improve cache locality, potentially leading to performance gains.

The primary motivation behind pinning is to improve performance by reducing latency and improving predictability. However, it is a technique that should be used carefully, as it can have unintended consequences if not properly managed. Overuse of pinning can lead to memory exhaustion, contention, and reduced overall system throughput. Understanding the specific context in which "pinned" is used is crucial for interpreting its meaning and impact.