GNU/Linux man pages
Livre :
Expressions régulières,
Syntaxe et mise en oeuvre :
GNU/Linux |
CentOS 4.8 |
i386 |
 |
poll(2) |
 |
poll − wait for some event on a file descriptor
#include <sys/poll.h>
int poll(struct pollfd *ufds, unsigned int nfds, int timeout);
poll is
a variation on the theme of select. It specifies an
array of nfds structures of type
struct pollfd {
int fd; /* file descriptor */
short events; /* requested events */
short revents; /* returned events */
};
and a timeout in milliseconds. A negative value means
infinite timeout. The field fd contains a file
descriptor for an open file. The field events is an
input parameter, a bitmask specifying the events the
application is interested in. The field revents is an
output parameter, filled by the kernel with the events that
actually occurred, either of the type requested, or of one
of the types POLLERR or POLLHUP or
POLLNVAL. (These three bits are meaningless in the
events field, and will be set in the revents
field whenever the corresponding condition is true.) If none
of the events requested (and no error) has occurred for any
of the file descriptors, the kernel waits for timeout
milliseconds for one of these events to occur. The following
possible bits in these masks are defined in
<sys/poll.h>
#define POLLIN 0x0001 /* There is data to read */
#define POLLPRI 0x0002 /* There is urgent data to read */
#define POLLOUT 0x0004 /* Writing now will not block */
#define POLLERR 0x0008 /* Error condition */
#define POLLHUP 0x0010 /* Hung up */
#define POLLNVAL 0x0020 /* Invalid request: fd not open */
When compiling XPG4.2 source one also has
#ifdef _XOPEN_SOURCE
#define POLLRDNORM 0x0040 /* Normal data may be read */
#define POLLRDBAND 0x0080 /* Priority data may be read */
#define POLLWRNORM 0x0100 /* Writing now will not block */
#define POLLWRBAND 0x0200 /* Priority data may be written */
#endif
Finally, Linux knows about
#ifdef _GNU_SOURCE
#define POLLMSG 0x0400
#endif
On success, a positive number is returned, where the number returned is the number of structures which have non-zero revents fields (in other words, those descriptors with events or errors reported). A value of 0 indicates that the call timed out and no file descriptors have been selected. On error, −1 is returned, and errno is set appropriately.
|
EBADF |
An invalid file descriptor was given in one of the sets. | ||
|
ENOMEM |
There was no space to allocate file descriptor tables. | ||
|
EFAULT |
The array given as argument was not contained in the calling program’s address space. | ||
|
EINTR |
A signal occurred before any requested event. | ||
|
EINVAL |
The nfds value exceeds the RLIMIT_NOFILE value. |
XPG4-UNIX.
The poll() systemcall was introduced in Linux 2.1.23. The poll() library call was introduced in libc 5.4.28 (and provides emulation using select if your kernel does not have a poll syscall).
select(2), select_tut(2)
|
poll(2) | |