Unix系统整体介绍
2017-04-16
书本源代码
APUE学习方法
UNIX系统结构
UNIX系统术语
Input and Output
File Descriptor
非负整数，标志被进程处理的文件
Programs and Processes
Programs
A program is an executable file residing on disk in a directory. A program is read into memory and is executed by the kernel as a result of one of the seven exec functions.
Process
An executing instance of a program is called a process. The UNIX System guarantees that every process has a unique numeric identifier called the process ID.There are three primary functions for process control: fork, exec, and waitpid.
Threads
a process has only one thread of control — one set of machine instructions executing at a time. Some problems are easier to solve when more than one thread of control can operate on different parts of the problem. Additionally, multiple threads of control can exploit the parallelism possible on multiprocessor systems. All threads within a process share the same address space, file descriptors, stacks, and process-related attributes. Each thread executes on its own stack, although any thread can access the stacks of other threads in the same process. Because they can access the same memory, the threads need to synchronize access to shared data among themselves to avoid inconsistencies.
Signals
Signals are a technique used to notify a process that some condition has occurred.