Resources include memory (for both code and data), file handles, sockets, device handles, windows, and a process control block. Processes own resources allocated by the operating system. The term " light-weight process" variously refers to user threads or to kernel mechanisms for scheduling user threads onto kernel threads.Ī process is a "heavyweight" unit of kernel scheduling, as creating, destroying, and switching processes is relatively expensive. User threads may be executed by kernel threads in various ways (one-to-one, many-to-one, many-to-many). Cooperatively scheduled user threads are known as fibers different processes may schedule user threads differently. If these do not share data, as in Erlang, they are usually analogously called processes, while if they share data they are usually called (user) threads, particularly if preemptively scheduled. At the user level a process such as a runtime system can itself schedule multiple threads of execution. Kernel scheduling is typically uniformly done preemptively or, less commonly, cooperatively. At the kernel level, a process contains one or more kernel threads, which share the process's resources, such as memory and file handles – a process is a unit of resources, while a thread is a unit of scheduling and execution.
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