5、System V IPC与管道、FIFO通信机制详解

System V IPC与管道、FIFO通信机制详解

1. System V IPC概述

System V IPC（Inter - Process Communication）是一种重要的进程间通信机制，包含消息队列、信号量和共享内存三种类型。在创建或打开IPC对象时，会涉及一系列的逻辑判断。

下面是创建或打开IPC对象的逻辑流程图：

graph TD
    A[key == IPC - PRIVATE?] -->|Yes| B{system tables full?}
    B -->|Yes| C[error return, errno = ENOSPC]
    B -->|No| D[new entry is created]
    A -->|No| E{does key already exist?}
    E -->|No| F{IPC - CREAT set?}
    F -->|No| G[error return, errno = ENOENT]
    F -->|Yes| H{are both IPC - CREAT and IPC - EXCL set?}
    H -->|Yes| I[error return, errno = EEXIST]
    H -->|No| J[new entry is created]
    E -->|Yes| K{IPC - CREAT set?}
    K -->|Yes| L{are both IPC - CREAT and IPC - EXCL set?}