Reacting to file events.

The class CFileEvent allows an application to react asynchronously to events on a file. To use a CFileEvent you will need to:

• Decide which of the following conditions you need to supply application code for:
  1. Readbility (may be significant on e.g.
  2. Writability (may be significant e.g. pipes).
  3. Exceptional conditions (e.g. pipe broken).
• Write a subclass of CFile event which supplies the appropriate application specific functionality for any or all of the functions:
  1. OnReadable which is called when the file descriptor becomes readable.
  2. OnWritable which is called when the file descriptor becomes writable.
  3. OnException which is called when the file descriptor has an exceptional condition pending.
• During application execution create and enable an instance of this class.

In the example below, a file event is created to monitor stdin. When input is available on stdin, the first word of the line is echoed back on stdout.

#include <iostream.h>
#include <stdio.h>
#include <spectrodaq.h>
#include <SpectroFramework.h>

class Echo : public CFileEvent
{
public:
  Echo(int fd, const char* pName);
  virtual void OnReadable(istream& rin);
};

Echo::Echo(int fd, const char* pName):
  CFileEvent(fd, pName)
{
  AppendClassInfo();
}

void
Echo::OnReadable(istream& rin)
{
  CFileEvent::OnReadable(rin);
  string word;
  rin >> word;
  cout << word << endl;
}

class MyApp : public DAQROCNode
{
protected:
  virtual int operator()(int argc, char** argv);
};

int
MyApp::operator()(int argc, char** argv)
{
  Echo echo(fileno(stdin), "EchoProcessor");

  echo.Enable();
  DAQThreadId id = echo.getThreadId();

  Join(id);                     // Wait for echo to exit.
}


MyApp theapp;

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