rwlock.cpp

SMS gateway. SMS protocol for CHINA mobile, unicom, lingtong. Using mysql to exchange message.

//#include "stdafx.h"
#include "RWLock.h"
#include <iostream.h>
// read values from file
int RWLock::LockIn() {

  // open in file
  lockFile.open( RWLockFileName, ios::in );
  if (!lockFile) return ResetLock();

  // read from file
  lockFile >> Readers;
  lockFile >> Writers;

  // close file
  lockFile.close();

  return EXIT_SUCCESS;
}

// write values to file
int RWLock::LockOut() {
  enum open_mode { trunc = 020 };

  // open out file
  lockFile.open( RWLockFileName, ios::out|ios::trunc);
  if (!lockFile) {
    //cerr << "RWLock::LockOut: Cannot open lock file." << endl;
    return EXIT_FAILURE;
  }

  // write to file
  lockFile << Readers << "\n";
  lockFile << Writers << "\n";

  // close file
  lockFile.close();

  return EXIT_SUCCESS;
}

// reset values and write to lock file
int RWLock::ResetLock() {
    Readers = 0;
    Writers = 0;
    return LockOut();
}

// Initialization: create the file with extension RWLock
int RWLock::InitLock( char *fileName, unsigned int ts = 1 ) {
  struct stat fp;

  // sleep time in seconds
  RWsleep = ts;
  // create lock file name
  int len = strlen( fileName );
  if (!len) {
    //cerr << "RWLock::InitLock: Non-existing file name." << endl;
    return EXIT_FAILURE;
  }
  if (stat( fileName, &fp ) != 0) {
    //cerr << "RWLock::InitLock: Cannot lock a non-existing file." << endl;
    return EXIT_FAILURE;
  }

  RWLockFileName = new char[len + 8];
  strcpy( RWLockFileName, fileName );
  strcat( RWLockFileName, ".RWLock" );

  // check whether lock file exists, if not open it
  if (stat( RWLockFileName, &fp ) != 0) return ResetLock();

  return EXIT_SUCCESS;
}

// Obtain a reader lock.
int RWLock::ReadLock() {
  LockIn();
  while (Writers) {
    sleep( RWsleep );
    LockIn();
  }
  Readers++;
  return LockOut();
}

// Unlock reader lock
int RWLock::ReadUnLock() {
  LockIn();
  if (Readers == 0) return EXIT_FAILURE;
  Readers--;
  return LockOut();
}

// Obtain a writer lock
int RWLock::WriteLock() {
  LockIn();
  while (Writers || Readers) {
    sleep( RWsleep );
    LockIn();
  }
  Writers++;
  return LockOut();
}

// Release a writer lock
int RWLock::WriteUnLock() {
  LockIn();
  if (Writers == 0) return EXIT_FAILURE;
  Writers = 0;
  return LockOut();
}