系统V和Posix信号量之间的差异 [英] Differences between System V and Posix semaphores

问题描述

使用System V和Posix信号量之间的折衷是什么？

What are the trade-offs between using a System V and a Posix semaphore?

推荐答案

http://www.linuxdevcenter.com/pub/a/linux/2007/05/24/semaphores-in-linux.html?page=4rel =nofollow noreferrer> O'Reilly ：

From O'Reilly:

• System V和POSIX信号量之间的一个明显区别
  实现是在系统V
  可以控制多少信号量
  的计数可以增加或减少;
  ，而在POSIX中，信号量计数
  增加并减少1。


• POSIX信号量不允许操作信号量权限，
  ，信号量允许
  将
  信号量的权限更改为原始
  权限的子集。


• 信号量的初始化和创建是原子的


• 从用法的角度看，System V信号量是笨拙的，而POSIX
  信号量是直接的


• POSIX信号量（使用未命名的信号量）的可扩展性比系统V信号量多
  。在
  用户/客户端场景中，每个用户
  创建自己的服务器实例
  ，最好使用POSIX
  信号量。


• 系统V信号量在创建信号量对象时创建一个
  信号量数组，而POSIX信号量
  只创建一个。因为这个
  功能，与POSIX
  信号量相比，系统
  V中的信号量创建（内存
  占用空间）是昂贵的。


• 已经说POSIX信号量的性能优于
  基于系统V的信号量。


• POSIX信号量为进程范围的信号量提供了一种机制，而不是
  全系统信号量。所以，如果一个
  开发人员忘记关闭
  信号量，在进程退出
  信号量被清理。在简单的
  术语中，POSIX信号量为非持久的
  信号量提供
  机制。

• One marked difference between the System V and POSIX semaphore implementations is that in System V you can control how much the semaphore count can be increased or decreased; whereas in POSIX, the semaphore count is increased and decreased by 1.
• POSIX semaphores do not allow manipulation of semaphore permissions, whereas System V semaphores allow you to change the permissions of semaphores to a subset of the original permission.
• Initialization and creation of semaphores is atomic (from the user's perspective) in POSIX semaphores.
• From a usage perspective, System V semaphores are clumsy, while POSIX semaphores are straight-forward
• The scalability of POSIX semaphores (using unnamed semaphores) is much higher than System V semaphores. In a user/client scenario, where each user creates her own instances of a server, it would be better to use POSIX semaphores.
• System V semaphores, when creating a semaphore object, creates an array of semaphores whereas POSIX semaphores create just one. Because of this feature, semaphore creation (memory footprint-wise) is costlier in System V semaphores when compared to POSIX semaphores.
• It has been said that POSIX semaphore performance is better than System V-based semaphores.
• POSIX semaphores provide a mechanism for process-wide semaphores rather than system-wide semaphores. So, if a developer forgets to close the semaphore, on process exit the semaphore is cleaned up. In simple terms, POSIX semaphores provide a mechanism for non-persistent semaphores.

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