FBB::Selector(3bobcat)

Timed Delays, Multiple File I/O
(libbobcat-dev_4.08.03-x.tar.gz)

2005-2018

NAME

SYNOPSIS

DESCRIPTION

NAMESPACE

INHERITS FROM

CONSTRUCTORS

• Selector():
  This constructor initializes the object.

MEMBER FUNCTIONS

• void addExceptFd(int fd):
  Adds a filedescriptor to the set of file descriptors that are monitored for exceptions (note these are not C++ exceptions. See man 2 select for details).
• void addReadFd(int fd):
  Adds a filedescriptor to the set of file descriptors that are monitored for reading.
• void addWriteFd(int fd):
  Adds a filedescriptor to the set of file descriptors that are monitored for writing.
• int exceptFd():
  Returns -1 of no more file descriptors are available in the exception category. Otherwise the next available file descriptor in the exception category is returned. Returning from wait, this function can be called repeatedly until -1 is returned, servicing each available filedescriptor in turn.
• void noAlarm():
  This member prevents any timeout-alarm from occurring.
• int nReady():
  Returns the number of available file descriptors. 0 is returned at a timeout, -1: is returned when select(2) itself failed.
• int readFd():
  Returns -1 of no more file descriptors are available for reading. Otherwise the next available file descriptor for reading is returned. Returning from wait, this function can be called repeatedly until -1 is returned, servicing each available filedescriptor in turn. Note that the file whose file descriptor is returned by readFd may also be at its end-of-file position. The file is `ready for reading', but no characters will be returned when trying to read from it due to its end-of-file status. In that case the file descriptor is probably best removed from the set of active file descriptors.
• void rmExceptFd(int fd):
  Removes a filedescriptor from the set of file descriptors that are monitored for exceptions (note these are not C++ exceptions. See man 2 select for details).
• void rmReadFd(int fd):
  Removes a filedescriptor from the set of file descriptors that are monitored for reading.
• void rmWriteFd(int fd):
  Removes a filedescriptor from the set of file descriptors that are monitored for writing.
• void setAlarm(int sec, int usec = 0):
  This member sets the alarm at the indicated seconds and micro-seconds. If no action occurred on one of the monitored file descriptions following the indicated amount of time, wait will return with nReady returning 0. The requested alarm time (sec + usec / 1e+6) may not be negative and may not exceed std::numeric_limits<int>::max() or an FBB::Exception exception will be thrown. A 0 alarm time specification results in wait returning immediately. To switch off the alarm time use noAlarm.
• int wait():
  This member should be called to wait for activities on the installed file descriptors or timeout-period. The members exceptFd, nReady, readFd and writeFd show their defined behaviors only after wait has returned.

  It throws an FBB::Exception exception when select(2) fails, which may very well indicate the end of any available input. An exception is also thrown if the program received a signal.

  If wait returns normally its return value represents the number of available file descriptors. Note that wait may also return with an input file descriptor returned by readFd of a file at its end-of-file position. The file is `ready for reading', but no characters will be returned when trying to read from it due to its end-of-file status.

• int writeFd():
  Returns -1 of no more file descriptors are available for writing. Otherwise the next available file descriptor for writing is returned. Returning from wait, this function can be called repeatedly until -1 is returned, servicing each available filedescriptor in turn.

EXAMPLE

#include <string>
#include <iostream>

#include <bobcat/selector>
#include <bobcat/exception>

using namespace std;
using namespace FBB;

int main(int argc, char **argv, char **envp)
{
    Selector selector;

    selector.setAlarm(5);               // every 5 secs: alarm fires
    selector.addReadFd(STDIN_FILENO);   // look also at cin

    try
    {
        while (true)
        {
            if (!selector.wait())           // 0: alarm fires
                cout << "Are you still there?" << endl;                
            else
            {
                string s;
                if (!getline(cin, s) || !s.length())
                    return 0;
                cout << "Thank you for: " << s << endl;
            }
        }
    }
    catch (Exception const &e)
    {
        cout << e.what() << endl;
    }
    return 0;
}
    

FILES

SEE ALSO

BUGS

Facilities to prevent wait from waiting indefinitely in this situation will be added to Selector in a future Bobcat release.

DISTRIBUTION FILES

• bobcat_4.08.03-x.dsc: detached signature;
• bobcat_4.08.03-x.tar.gz: source archive;
• bobcat_4.08.03-x_i386.changes: change log;
• libbobcat1_4.08.03-x_*.deb: debian package holding the libraries;
• libbobcat1-dev_4.08.03-x_*.deb: debian package holding the libraries, headers and manual pages;
• http://sourceforge.net/projects/bobcat: public archive location;

BOBCAT

COPYRIGHT

AUTHOR