explain_select_or_die(3) Library Functions Manual explain_select_or_die(3)NAME
explain_select_or_die - blah blah and report errors
SYNOPSIS
#include <libexplain/select.h>
void explain_select_or_die(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
DESCRIPTION
The explain_select_or_die function is used to call the select(2) system call. On failure an explanation will be printed to stderr,
obtained from explain_select(3), and then the process terminates by calling exit(EXIT_FAILURE).
This function is intended to be used in a fashion similar to the following example:
explain_select_or_die(nfds, readfds, writefds, exceptfds, timeout);
nfds The nfds, exactly as to be passed to the select(2) system call.
readfds The readfds, exactly as to be passed to the select(2) system call.
writefds
The writefds, exactly as to be passed to the select(2) system call.
exceptfds
The exceptfds, exactly as to be passed to the select(2) system call.
timeout The timeout, exactly as to be passed to the select(2) system call.
Returns:
This function only returns on success. On failure, prints an explanation and exits.
SEE ALSO select(2)
blah blah
explain_select(3)
explain select(2) errors
exit(2) terminate the calling process
COPYRIGHT
libexplain version 0.52
Copyright (C) 2008 Peter Miller
explain_select_or_die(3)
Check Out this Related Man Page
select(2) System Calls Manual select(2)Name
select - synchronous I/O multiplexing
Syntax
#include <sys/types.h>
#include <sys/time.h>
int select (nfds, readfds, writefds, exceptfds, timeout)
int nfsd;
fd_set *readfds, *writefds, *exceptfds;
struct timeval *timeout;
FD_SET (fd, fdset)
FD_CLR (fd, fdset)
FD_ISSET (fd, fdset)
FD_ZERO (fdset)
int fd;
fd_set *fdset;
Description
The system call examines the I/O descriptor sets whose addresses are passed in readfds, writefds, and exceptfds to see if some of their
descriptors are ready for reading, ready for writing, or have an exceptional condition pending. The nfds parameter is the number of bits to
be checked in each bit mask that represent a file descriptor; the descriptors from 0 through nfds-1 in the descriptor sets are examined.
Typically nfds has the value returned by for the maximum number of file descriptors. On return, replaces the given descriptor sets with
subsets consisting of those descriptors that are ready for the requested operation. The total number of ready descriptors in all the sets
is returned.
The descriptor sets are stored as bit fields in arrays of integers. The following macros are provided for manipulating such descriptor
sets: FD_ZERO(fds descriptor set fdset to the null set. FD_SET(fd, fdset) includes a particular descriptor fd in fdset. FD_CLR(fd, fdset)
removes fd from fdset. FD_ISSET(fd, fdset) is nonzero if fd is a member of fdset, zero otherwise. The behavior of these macros is undefined
if a descriptor value is less than zero or greater than or equal to FD_SETSIZE, which is equal to the maximum number of descriptors that
can be supported by the system.
If timeout is not a NULL pointer, it specifies a maximum interval to wait for the selection to complete. If timeout is a NULL pointer, the
select blocks indefinitely. To effect a poll, the timeout argument should be a non-NULL pointer, pointing to a zero-valued timeval struc-
ture.
Any of readfds, writefds, and exceptfds may be given as NULL pointers if no descriptors are of interest.
Selecting true for reading on a socket descriptor upon which a call has been performed indicates that a subsequent call on that descriptor
will not block.
Restrictions
The call may indicate that a descriptor is ready for writing when in fact an attempt to write would block. This can happen if system
resources necessary for a write are exhausted or otherwise unavailable. If an application deems it critical that writes to a file descrip-
tor not block, it should set the descriptor for non-blocking I/O using the F_SETFL request to the call.
Return Values
The call returns a non-negative value on success. A positive value indicates the number of ready descriptors in the descriptor sets. A 0
indicates that the time limit referred to by timeout expired. On failure, returns -1, sets errno to indicate the error, and the descriptor
sets are not changed.
Diagnostics
[EBADF] One of the descriptor sets specified an invalid descriptor.
[EFAULT] One of the pointers given in the call referred to a non-existent portion of the process' address space.
[EINTR] A signal was delivered before any of the selected events occurred, or before the time limit expired.
[EINVAL] A component of the pointed-to time limit is outside the acceptable range; t_sec must be between 0 and 10^8, inclusive. t_usec
must be greater than or equal to 0, and less than 10^6.
See Alsoaccept(2), connect(2), fcntl(2), gettimeofday(2), listen(2), read(2), recv(2), send(2), write(2), getdtablesize(2)select(2)