Talk:Asynchronous I/O
From Wikipedia, the free encyclopedia
< Talk:Asynchronous I
Non-blocking and async are not quite synonyms:
- Non-blocking refers to using normal I/O primitives in non-blocking mode, e.g. the O_NONBLOCK flag to open(2), where calls to read(2) and write(2) return -1 with errno set to EAGAIN if I/O would block.
- Async refers to separating checks for the availability of I/O, potentially on many fds, and actually doing the I/O. For example, one may use the O_ASYNC flag to open(2), wait for the kernel to send SIGIO, and then use non-blocking calls to actually do the I/O; or call select(2) with a set of fds to wait for I/O to become available on one of them, then use read(2) and write(2) to do I/O on any fds which have data waiting.
The technique of spawning a thread to block on a single fd each waiting for I/O while the main thread carries on with processing can also be described as async, but does it using blocking calls. Hairy Dude 19:31, 24 May 2006 (UTC)
- That's how the terms are used in C/POSIX. I suspect that some other culture (probably Java?) calls (emulated) asynchronous IO "non-blocking IO" and thus the confusion. Any Java programmers who can enlighten us? --Doc aberdeen 14:13, 27 February 2007 (UTC)
