select.2 (2010 09)

ManualsBrandsHP ManualsSoftwareHP-UX Manpages

select(2) select(2)

NAME

select(), pselect(), FD_CLR(), FD_ISSET(), FD_SET(), FD_ZERO() - synchronous I/O multiplexing

SYNOPSIS

#include <sys/select.h>

#include <sys/time.h>

int pselect(int nfds, fd_set *__restrict readfds,

fd_set *__restrict writefds, fd_set *__restrict errorfds,

const struct timespec *__restrict timeout,

const sigset_t *__restrict sigmask);

#include <sys/time.h>

int select(int nfds, fd_set *__restrict readfds,

fd_set *__restrict writefds, fd_set *__restrict errorfds

struct timeval *__restrict timeout);

void FD_CLR(int fd, fd_set *fdset);

int FD_ISSET(int fd, fd_set *fdset);

void FD_SET(int fd, fd_set *fdset);

void FD_ZERO(fd_set *fdset);

For Backward Compatibility Only: (_XOPEN_SOURCE_EXTENDED not deﬁned)

#include <time.h>

int select(size_t nfds, int *readfds, int *writefds,

int *exceptds, const struct timeval *timeout);

DESCRIPTION

The pselect() and select() functions indicate which of the speciﬁed ﬁle descriptors is ready for

reading, ready for writing, or has an error condition pending. If the speciﬁed condition is false for all of

the speciﬁed ﬁle descriptors, pselect() and select() block, up to the speciﬁed timeout interval,

until the speciﬁed condition is true for at least one of the speciﬁed ﬁle descriptors.

The

pselect() and select() functions support regular ﬁles, terminal and pseudo-terminal devices,

STREAMS-based ﬁles, FIFOs and pipes. The behaviour of

pselect() and select() on ﬁle descrip-

tors that refer to other ﬁle types is unspeciﬁed.

The nfds argument speciﬁes the range of ﬁle descriptors to be tested. The

pselect() and select()

functions test ﬁle descriptors in the range of 0 to nfds −1. File descriptor f is represented by the bit 1<<f

in the masks. More formally, a ﬁle descriptor is represented by:

fds[(f / BITS_PER_INT)] & (1 << (f % BITS_PER_INT))

If the readfds argument is not a null pointer, it points to an object of type fd_set that on input speciﬁes

the ﬁle descriptors to be checked for being ready to read, and on output indicates which ﬁle descriptors

are ready to read.

If the writefds argument is not a null pointer, it points to an object of type fd_set that on input speciﬁes

the ﬁle descriptors to be checked for being ready to write, and on output indicates which ﬁle descriptors

are ready to write.

If the errorfds argument is not a null pointer, it points to an object of type fd_set that on input speciﬁes

the ﬁle descriptors to be checked for error conditions pending, and on output indicates which ﬁle descrip-

tors have error conditions pending.

On successful completion, the objects pointed to by the readfds , writefds , and errorfds arguments are

modiﬁed to indicate which ﬁle descriptors are ready for reading, ready for writing, or have an error condi-

tion pending, respectively. For each ﬁle descriptor less than nfds, the corresponding bit will be set on

successful completion if it was set on input and the associated condition is true for that ﬁle descriptor.

If the timeout argument is not a null pointer, it speciﬁes a maximum interval to wait for the selection to

complete. The timeout argument points to an object of type

struct timespec for pselect(), and to

an object of type struct timeval for select(). If the members of these structures are 0,

pselect() or select() will not block. If the timeout argument is a null pointer, pselect() or

select() will block until an event causes one of the masks to be returned with a valid (non-zero) value.

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (6 pages)

PAGE 1
select(2) select(2) NAME select(), pselect(), FD_CLR(), FD_ISSET(), FD_SET(), FD_ZERO() - synchronous I/O multiplexing SYNOPSIS #include #include int pselect(int nfds, fd_set *__restrict readfds, fd_set *__restrict writefds, fd_set *__restrict errorfds, const struct timespec *__restrict timeout, const sigset_t *__restrict sigmask); #include
PAGE 2
select(2) select(2) If the time limit expires before any event occurs that would cause one of the masks to be set to a non-zero value, pselect() or select() completes successfully and returns 0. Implementations may place limitations on the maximum timeout interval supported. On all implementations, the maximum timeout interval supported will be at least 31 days.
PAGE 3
select(2) select(2) The use of a timeout does not affect any pending timers set up by alarm(), ualarm(), or setitimer(). On successful completion, the object pointed to by the timeout argument of select() may be modified. The FD_SETSIZE is used in the definition of fd_set structure. It is set to a value of 2048 to accommodate 2048 file descriptors.
PAGE 4
select(2) select(2) EXAMPLES The following call to select() checks if any of 4 terminals are ready for reading. select() times out after 5 seconds if no terminals are ready for reading. Note that the code for opening the terminals or reading from the terminals is not shown in this example. Also, note that this example must be modified if the calling process has more than 32 file descriptors open. Following this first example is an example of select with more than 32 file descriptors.
PAGE 5
select(2) select(2) for (k=0; k < NWORDS; k++) readmask.fds_bits[k] = 0; for (i=0, k=0; i < NTTYS && k < NWORDS; k++) for (j=0; j < NFDBITS && i < NTTYS; j++, i++) { ttymask[i] = MASK(tty[i]); readmask.fds_bits[k] |= ttymask[i]; } timeout.tv_sec = 5; timeout.tv_usec = 0; for (k=0; k < NWORDS; k++) readfds.fds_bits[k] = readmask.
PAGE 6
(Notes) A (Notes) sA 6 Hewlett-Packard Company −1− HP-UX 11i Version 3: September 2010