User:Rob Kennedy/Signals
- This is not a real article. It’s here for testing changes to the signal-related articles.
| Description: | Pollable event (Sys V) |
|---|---|
| Default action: | Abnormal termination of the process |
| SA_SIGINFO macros | |
POLL_IN
|
Data input available |
POLL_OUT
|
Output buffers available |
POLL_MSG
|
Input message available |
POLL_ERR
|
I/O error |
POLL_PRI
|
High priority input available |
POLL_HUP
|
Device disconnected |
On POSIX-compliant platforms, SIGPOLL is the signal thrown by computer programs when a user wishes to interrupt the process. The symbolic constant for SIGPOLL is defined in the header file signal.h. Symbolic signal names are used because signal numbers can vary across platforms.
On Linux, SIGIO is a synonym for SIGPOLL.
Etymology
[edit]SIG is a common prefix for signal names. POLL refers to polling, in the context of the poll system call. IO stands for input/output.
Usage
[edit]As specified by POSIX, when the F_SETSIG operation is performed on a file descriptor with the fcntl system call, the kernel is instructed to signal the calling process when a pollable event (i.e. one which would interrupt the poll system call) occurs on the file descriptor; for example when input or output becomes possible. The signal sent may be user-specified, but defaults to SIGPOLL. By employing this mechanism, the user may accomplish true asynchronous I/O without the conceptual overhead of a multiplexing select loop. A possible disadvantage is that the technique lends itself to producing spaghetti code, with race conditions a danger.
From POSIX 1003.1 (2003), it is preferred to use the standardised system calls for asynchronous I/O defined in aio.h. These allow requests to be queued for asynchronous execution; return and error status can be retrieved with the aio_return and aio_error functions, respectively.