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| <h3 class="section">15.4 Atomicity of Pipe I/O</h3> |
| |
| <p>Reading or writing pipe data is <dfn>atomic</dfn> if the size of data written |
| is not greater than <code>PIPE_BUF</code>. This means that the data transfer |
| seems to be an instantaneous unit, in that nothing else in the system |
| can observe a state in which it is partially complete. Atomic I/O may |
| not begin right away (it may need to wait for buffer space or for data), |
| but once it does begin it finishes immediately. |
| |
| <p>Reading or writing a larger amount of data may not be atomic; for |
| example, output data from other processes sharing the descriptor may be |
| interspersed. Also, once <code>PIPE_BUF</code> characters have been written, |
| further writes will block until some characters are read. |
| |
| <p>See <a href="Limits-for-Files.html#Limits-for-Files">Limits for Files</a>, for information about the <code>PIPE_BUF</code> |
| parameter. |
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