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A process with two threads of execution, running on one processor Program vs. Process vs. Thread Scheduling, Preemption, Context Switching. In computer science, a thread of execution is the smallest sequence of programmed instructions that can be managed independently by a scheduler, which is typically a part of the operating system. [1]
For example: Cycle i: instruction j from thread A is issued. Cycle i + 1: instruction j + 1 from thread A is issued. Cycle i + 2: instruction j + 2 from thread A is issued, which is a load instruction that misses in all caches. Cycle i + 3: thread scheduler invoked, switches to thread B. Cycle i + 4: instruction k from thread B is issued.
On many machines direct-threading is faster than subroutine threading (see reference below). An example of a stack machine might execute the sequence "push A, push B, add". That might be translated to the following thread and routines, where ip is initialized to the address labeled thread (i.e., the address where &pushA is stored).
Software libraries can provide certain thread-safety guarantees. [5] For example, concurrent reads might be guaranteed to be thread-safe, but concurrent writes might not be. Whether a program using such a library is thread-safe depends on whether it uses the library in a manner consistent with those guarantees.
Coarse-grain multithreading is more common for less context switch between threads. For example, Intel's Montecito processor uses coarse-grained multithreading, while Sun's UltraSPARC T1 uses fine-grained multithreading. For those processors that have only one pipeline per core, interleaved multithreading is the only possible way, because it ...
In computer programming, thread-local storage (TLS) is a memory management method that uses static or global memory local to a thread. The concept allows storage of data that appears to be global in a system with separate threads. Many systems impose restrictions on the size of the thread-local memory block, in fact often rather tight limits.
Barrel processors are also found in embedded systems, where they are particularly useful for their deterministic real-time thread performance. An early example is the “Dual CPU” version of the four-bit COP400 that was introduced by National Semiconductor in 1981. This single-chip microcontroller contains two ostensibly independent CPUs that ...
In both cases, the features must be part of the language syntax and not an extension such as a library (libraries such as the posix-thread library implement a parallel execution model but lack the syntax and grammar required to be a programming language).