Linux System Programming by unknow

Author:unknow
Language: eng
Format: epub
Tags: COMPUTERS / Operating Systems / UNIX
Publisher: O’Reilly Media
Published: 2013-05-14T04:00:00+00:00

Multithreading

What is the point of threads? We obviously need processes, since they are the abstraction of a running program. But why decouple the unit of execution and introduce threads? There are six primary benefits to multithreading:

Programming abstraction

Dividing up work and assigning each division to a unit of execution (a thread) is a natural approach to many problems. Design patterns that utilize this approach include the thread-per-connection and thread pool patterns. Programmers find these patterns useful and intuitive. Some, however, view threads as an anti-pattern. The inimitable Alan Cox summed this up well with the quote, “threads are for people who can’t program state machines.” That is, there is in theory no programming problem that is solvable with threads that isn’t solvable with a state machine.

Parallelism

In machines with multiple processors, threads provide an efficient way to achieve true parallelism. As each thread receives its own virtualized processor and is an independently schedulable entity, multiple threads may run on multiple processors at the same time, improving a system’s throughput. To the extent that threads are used to achieve parallelism—that is, there are no more threads than processors—the “threads are for people who can’t program state machines” maxim does not apply.

Improving responsiveness

Even on a uniprocessor machine, multithreading can improve a process’s responsiveness. In a single-threaded process, a long-running operation can prevent an application from responding to user input, making it appear as if the application has froze. With multithreading, such operations may be delegated to worker threads, allowing at least one thread to remain responsive to user input and perform UI operations.

Blocking I/O

This is related to the previous item. Without threads, blocking I/O halts the entire process. This can be detrimental to both throughput and latency. In a multithreaded process, individual threads may block, waiting on I/O, while other threads continue to make forward progress. Asynchronous and nonblocking I/O are alternative solutions to threads for this issue.

Context switching

The cost of switching from one thread to a different thread within the same process is significantly cheaper than process-to-process context switching.

Memory savings

Threads provide an efficient way to share memory yet utilize multiple units of execution. In this manner they are an alternative to multiple processes.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.