brukernivåtråder

User-level threads, often referred to as "brukernivåtråder" in Norwegian, represent a programming concept in concurrent programming. They are threads managed by the user-level application rather than the operating system kernel. This means that the thread management, such as creation, scheduling, and destruction, is handled by a library or runtime environment within the program itself.

The primary advantage of user-level threads is their speed. Because the operating system kernel is not involved in every thread operation, context switching between user-level threads is significantly faster than switching between kernel-level threads. This is because kernel involvement requires system calls, which incur overhead. Furthermore, a single kernel thread can support multiple user-level threads, allowing for a very large number of threads to exist within a process without overwhelming the operating system.

However, user-level threads also have drawbacks. One significant limitation is that if one user-level thread within a kernel thread makes a blocking system call, the entire kernel thread (and thus all other user-level threads mapped to it) will be blocked. This can negate the benefits of concurrency. Additionally, user-level threads cannot take advantage of multiple processor cores directly, as they are all multiplexed onto the same kernel thread. If true parallelism is required, kernel-level threads or a hybrid approach are usually necessary. Libraries like POSIX Threads (pthreads) can be implemented as either user-level or kernel-level threads, or a combination of both, depending on the system and configuration.