This is incorrect about pipes in UNIX-like OSs:

Question

BlackTom AI · Accepted Answer

Pipes are unidirectional byte streams implemented by the kernel, so their semantics determine which statement is incorrect.

1. Relevant knowledge points and concepts
- pipe() creates two file descriptors: one for reading, one for writing (fd[0], fd[1]).
- Pipes are unidirectional: data flows from write end to read end.
- The kernel treats pipes as byte streams (or FIFOs for named pipes); reads consume bytes from the buffer.
- Multiple-reader semantics: if several processes read from the same pipe, the kernel distributes available bytes among the readers (not duplicating them).
- Broadcasting (sending the same message copy to many receivers) is not provided by pipes; different IPC (multicast sockets, publish/subscribe systems, or explicit multiple writes/copies) is required.

2. Step-by-step reasoning
- pipe() returns two descriptors: confirm read and write ends exist.
- A writer writes N bytes into the pipe buffer; the kernel stores them once.
- A single reader calling read() consumes bytes; if several readers exist, each read takes a portion; there is no kernel-level replication of the same bytes to all readers.
- Therefore, the pipe cannot natively broadcast a single write to multiple processes.

3. Calculations / intermediate steps
- Example: Writer writes "HELLO" (5 bytes). Two readers concurrently read: Reader A may receive "HE", Reader B "LLO" (distribution depends on scheduling). No copy of "HELLO" is delivered to both.

4. Why the correct answer is correct
- "can support broadcasting messages to multiple processes" is incorrect because pipes provide single-stream semantics where data is consumed, not duplicated to multiple consumers.

5. Why other options are correct/incorrect
- "is uni-directional": correct for standard pipes.
- "has input and output that can be accessed programmatically through file descriptors": correct (fd[0], fd[1]).
- "has a read end and a write end": correct (explicit ends created by pipe()).

6. Conclusion
The incorrect statement is "can support broadcasting messages to multiple processes", which matches the provided answer.

This is incorrect about pipes in UNIX-like OSs:单项选择题

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