c - 原子写入文件描述符

Question

我正在阅读 pipe(7) s 在 Linux 中遇到了以下事情:

POSIX.1 says that write(2)s of less than PIPE_BUF bytes must be atomic: the output data is written to the pipe as a contiguous sequence. Writes of more than PIPE_BUF bytes may be nonatomic: the kernel may interleave the data with data written by other processes. POSIX.1 requires PIPE_BUF to be at least 512 bytes. (On Linux, PIPE_BUF is 4096 bytes.)

这个不是很清楚。 POSIX 是否要求所有小于 PIPE_BUF 的写入都是原子的？或者这仅适用于使用 pipe(int[2], int) 创建的管道？

Answer 1

引用的行为是特定于管道的(但适用于所有管道，无论它们是如何创建的(例如通过pipe、mkfifo+open 等))。

来自POSIX description of write :

Write requests to a pipe or FIFO shall be handled in the same way as a regular file with the following exceptions:

• [...]

• Write requests of {PIPE_BUF} bytes or less shall not be interleaved with data from other processes doing writes on the same pipe. Writes of greater than {PIPE_BUF} bytes may have data interleaved, on arbitrary boundaries, with writes by other processes, whether or not the O_NONBLOCK flag of the file status flags is set.