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The term "light-weight process" variously refers to user threads or to kernel mechanisms for scheduling user threads onto kernel threads. A process is a "heavyweight" unit of kernel scheduling, as creating, destroying, and switching processes is relatively expensive.
In computer operating systems, a light-weight process (LWP) is a means of achieving multitasking.In the traditional meaning of the term, as used in Unix System V and Solaris, a LWP runs in user space on top of a single kernel thread and shares its address space and system resources with other LWPs within the same process.
For example, hardware interrupt threads have the highest priority, followed by software interrupts, kernel-only threads, then finally user threads. A user thread either runs at user-kernel priority (when it is actually running in the kernel, e.g. running a syscall on behalf of userland), or a user thread runs at user priority. DragonFly does ...
FreeBSD uses a multilevel feedback queue with priorities ranging from 0–255. 0–63 are reserved for interrupts, 64–127 for the top half of the kernel, 128–159 for real-time user threads, 160–223 for time-shared user threads, and 224–255 for idle user threads. Also, like Linux, it uses the active queue setup, but it also has an idle ...
A common form of multitasking is provided by CPU's time-sharing that is a method for interleaving the execution of users' processes and threads, and even of independent kernel tasks – although the latter feature is feasible only in preemptive kernels such as Linux. Preemption has an important side effect for interactive processes that are ...
Then the operating system calls the switch() routine to first save the general-purpose user registers of A onto A's kernel stack, then it saves A's current kernel register values into the PCB of A, restores kernel registers from the PCB of process B, and switches context, that is, changes kernel stack pointer to point to the kernel stack of ...
In general, "N:M" threading systems are more complex to implement than either kernel or user threads, because both changes to kernel and user-space code are required. Scheduler activations were proposed by Anderson, Bershad, Lazowska, and Levy in Scheduler Activations: Effective Kernel Support for the User-Level Management of Parallelism in ...
Threads created by the library (via pthread_create) correspond one-to-one with schedulable entities in the kernel (processes, in the Linux case). [4]: 226 This is the simplest of the three threading models (1:1, N:1, and M:N). [4]: 215–216 New threads are created with the clone() system call called through the