/// <summary>
/// Defeats the protocol by removing the file and replacing it with one that contains the
/// new process identifier -
/// </summary>
/// <param name="sem">A FileSempahore</param>
/// <returns>True if successfull.</returns>
private static bool ForceLock(ref FileSemaphore sem)
{
if (sem.RemoveLock() == false)
{
return(false);
}
return(Lock(ref sem));
}
/// <summary>
/// <para>Write to the log file in such a way so as to avoid collisions in updating same.</para>
/// <para>NOTE: THIS PROCESS USES LockWait. IF YOU ARE USING IT ACROSS MACHINES, THERE IS A SLIGHT CHANCE
/// THAT YOUR PROCESS ID WILL NOT BE UNIQUE. CAVEAT USER.</para>
/// </summary>
/// <param name="sMessage">The message to write.</param>
/// <returns>True if the log file was written.</returns>
public bool LogWait(string sMessage)
{
bool br = false;
if (FileSemaphore.LockWait(ref fSem) == true)
{
if (SimpleLog.Log(sMessage) != null)
{
br = true;
}
FileSemaphore.UnLock(ref fSem);
}
return(br);
}
/// <summary>
/// Lock a semaphore file. You can only UnLock a semaphore that either does not exists, or that your process
/// has previously Locked.
/// </summary>
/// <param name="sem">A semaphore file (context)</param>
/// <returns>True if the semaphore file was released.</returns>
public static bool UnLock(ref FileSemaphore sem)
{
// STEP: If the semaphore file is not there, then the resource is unlocked.
if (sem.IsLocked() == false)
{
return(true);
}
// STEP: The general public can ONLY remove a semaphore file IF it is theirs
if (sem.iSemCode == sem.GetSemaphore())
{
return(sem.RemoveLock());
}
// Otherwise the user CANNOT unlock it!
return(false);
}
/// <summary>
/// You can only Lock a file if the semaphore file does not exist.
/// Use LockWait if you want to honor the timeout mechanism - otherwise
/// it is COMPLETELY ignored -
/// </summary>
/// <param name="sem">A semaphore file (context)</param>
/// <returns>Returns true if the semaphore was updated to your process ID.</returns>
public static bool Lock(ref FileSemaphore sem)
{
// STEP: If it is locked, see if we have locked it -
if (sem.IsLocked() == true)
{
int iResult = sem.GetSemaphore();
// See if it is already locked - by us
if (iResult == sem.iSemCode)
{
return(true);
}
// See if it was just removed -
if (iResult != 0)
{
return(false);
}
}
// STEP: Lock it -
return(sem.SetSemaphore(sem.iSemCode));
}
/// <summary>
/// The ONLY place where the lock timeous is honored.
/// </summary>
/// <param name="sem">A semaphore file (context)</param>
/// <returns>True when you are able to obtain a lock.</returns>
public static bool LockWait(ref FileSemaphore sem)
{
if (sem.IsLocked())
{
DateTime dtMax = DateTime.Now;
// DESIRED: No matter who has locked it (even us!), ForceLock the
// file if it has been around longer that it should have been -
// - OBSERVED -
// This is an odd fish - Sometimes the test case reports that
// the file was written (or created) when we actually did so,
// other times it just seems to take the value for the last
// time the inode was created / written to... This type of
// recovery is not on the critical path the moment, so we will
// move on -
// TODO: Resolve or report the above issue.
/*
* DateTime dtActual = File.GetLastWriteTime(sem.sFQSemFile);
* dtActual = dtActual.AddSeconds(sem.dSec);
* if(dtActual < dtMax)
* return ForceLock(ref sem);
*/
// Set the most recent time to the future -
dtMax = dtMax.AddSeconds(sem.dSec);
// Prime the semaphore that we need to start timing -
int iHasIt = sem.GetSemaphore();
// STEP: If we have locked it, then just leave it -
if (iHasIt == sem.iSemCode)
{
return(true);
}
// STEP: Block while there is a lock file -OR- until a
// process has locked the recource for the specified
// recource timeout limit -
while (sem.IsLocked() == true)
{
int iPeek = sem.GetSemaphore();
if (iPeek == 0)
{
continue;
}
if (iPeek == iHasIt)
{
if (DateTime.Now > dtMax)
{
return(ForceLock(ref sem)); // Time to FORCE the issue -
}
}
else
{
dtMax = DateTime.Now;
dtMax.AddSeconds(sem.dSec);
}
}
}
// STEP: The file is no longer there - Lock it -
return(Lock(ref sem));
}
/// <summary>
/// Use this constructor to share a log file ACROSS MANY machines AND operating systems.
/// It allows you to place a file AND it's locking mechanism wherever you have access
/// (across a LAN, etc.)
/// </summary>
/// <param name="sFQFileName">A fully qualified file log name.</param>
public SharedSimpleLog(string sFQFileName)
{
log.FileName = sFQFileName;
fSem = new FileSemaphore(log.FileName);
}
/// <summary>
/// Use this constructor to allow processes on the SAME MACHINE to share a MACHINE NAMED logging file.
/// The file will be placed in the CURRENT DIRECTORY.
/// </summary>
public SharedSimpleLog()
{
fSem = new FileSemaphore(log.FileName);
}