/// <summary>
/// Helper function that adjusts the ready list based upon recent changes
/// </summary>
private void Scheduler(ProcessControlBlock process)
{
ProcessControlBlock p = null;
for (var i = 2; i >= 0; i--)
{
if (ReadyList[i].Count > 0)
{
p = ReadyList[i][0];
break;
}
}
if (p == null)
{
throw new Exception("No processes running: EXTREME FAILURE!");
}
if (process == null ||
process.Priority < p.Priority ||
process.StatusType != ProcessStates.Running)
{
p.StatusType = ProcessStates.Running;
RunningProcess = p;
}
}
/// <summary>
/// Creates a new new process <name> at the priority level <priority>;
/// <name> is a single character; <priority> can be a 1 or 2 (0 is reserved for Init process).
/// </summary>
/// <param name="name">The process name.</param>
/// <param name="priority">The process priority.</param>
public void Create(char name, int priority)
{
// Error if priority is not 1 or 2
if (priority != 1 && priority != 2)
{
throw new Exception("Priority must be 1 or 2");
}
// Recursively search children tree of the init process to see if process id already exists
if (FindProcessById(name.ToString(), ReadyList[0][0]) != null)
{
throw new Exception(String.Format("duplicate process name: {0}", name));
}
// Create new Process
var process = new ProcessControlBlock(name.ToString(), (Priorities)priority);
// Initialize process
process.StatusList = ReadyList;
process.Parent = RunningProcess;
// Update parent process
RunningProcess.Children.Add(process);
// Add process to ready list
ReadyList[priority].Add(process);
Scheduler(process);
}
/// <summary>
/// Initializes the Process and Resource manager state back to the original
/// state.
/// </summary>
public void Initialize()
{
// Initialize the ready list
ReadyList = new List <ProcessControlBlock>[3]
{
new List <ProcessControlBlock>(),
new List <ProcessControlBlock>(),
new List <ProcessControlBlock>()
};
// Create new Process
var process = new ProcessControlBlock("init", Priorities.Init);
// Initialize process
process.StatusList = ReadyList;
// Add process to ready list
ReadyList[0].Add(process);
// Create resources
Resources = new List <ResourceControlBlock>()
{
new ResourceControlBlock("R1", 1),
new ResourceControlBlock("R2", 2),
new ResourceControlBlock("R3", 3),
new ResourceControlBlock("R4", 4),
};
Scheduler(process);
}
/// <summary>
/// Helper method used to release the resource. This function is the core of the "Release"
/// function, but is used because "Kill Tree" also recursively releases resources on delete.
/// </summary>
/// <param name="process">The process.</param>
/// <param name="resource">The resource.</param>
/// <param name="units">The units.</param>
/// <exception cref="Exception">
/// </exception>
private void ReleaseResource(ProcessControlBlock process, ResourceControlBlock resource, int units)
{
// Validate that the process has units from the resource
if (!process.OtherResources.Where(x => x.Key == resource).Select(y => y).Any())
{
throw new Exception(String.Format("not holding resource: {0}", resource.Rid));
}
// Is the release attempting to release too many units
if (resource.CurUnits + units > resource.MaxUnits)
{
throw new Exception(String.Format("release too many units: {0}/{1}:{2}", units, resource.Rid, resource.MaxUnits - resource.CurUnits));
}
// Reduce the allocated units from resource units pair
var resourceUnits = process.OtherResources.First(x => x.Key == resource);
var newPair = new KeyValuePair <ResourceControlBlock, int>(resourceUnits.Key,
resourceUnits.Value - units);
// process is no longer using resource
if (newPair.Value == 0)
{
process.OtherResources.Remove(process.OtherResources.First(x => x.Key.Equals(resource)));
}
else
{
process.OtherResources.Remove(
RunningProcess.OtherResources.First(x => x.Key == resourceUnits.Key));
RunningProcess.OtherResources.Add(newPair);
}
resource.CurUnits += units;
// loop through all waiting processes to get access to resource
while (resource.WaitingList.Count != 0 && resource.WaitingList[0].Value <= resource.CurUnits)
{
// Get process from waiting list
process = resource.WaitingList[0].Key;
// Get requested amount of resource
var u = resource.WaitingList.First(x => x.Key.Equals(process)).Value;
// Remove units from resource
resource.CurUnits -= u;
// Remove process from waiting list
resource.WaitingList.RemoveAt(0);
// Add resource to process list
process.StatusType = ProcessStates.Ready;
process.StatusList = ReadyList;
process.OtherResources.Add(new KeyValuePair <ResourceControlBlock, int>(resource, u));
// Insert process into ready list
ReadyList[(int)process.Priority].Add(process);
}
}
/// <summary>
/// Recursive function that searches for the process by identifier.
/// </summary>
/// <param name="id">The identifier.</param>
/// <param name="process">The current process.</param>
/// <returns></returns>
private static ProcessControlBlock FindProcessById(string id, ProcessControlBlock process)
{
if ((process == null) || process.Pid == id)
{
return(process);
}
// recursively navigate through tree to find process, otherwise return null
foreach (var proc in process.Children)
{
var p = FindProcessById(id, proc);
if (p != null)
{
return(p);
}
}
return(null);
}
/// <summary>
/// Timesouts the manager and shifts the current running process to the back of it's queue,
/// and sets the current running process to the next in line.
/// </summary>
public void Timeout()
{
ProcessControlBlock process = null;
for (var i = 2; i >= 0; i--)
{
if (ReadyList[i].Count > 0)
{
process = ReadyList[i][0];
break;
}
}
ReadyList[(int)process.Priority].Remove(process);
process.StatusType = ProcessStates.Ready;
ReadyList[(int)process.Priority].Add(process);
Scheduler(process);
}
/// <summary>
/// Releases resources from all children nodes and from process.
/// </summary>
/// <param name="process">The process.</param>
private void KillTree(ProcessControlBlock process)
{
if (process == null)
{
return;
}
foreach (var proc in process.Children)
{
KillTree(proc);
}
// remove all children
process.Children = null;
// if process is blocked by resource, remove process from waiting list
if (process.StatusType == ProcessStates.Blocked)
{
var resource = (ResourceControlBlock)process.StatusList;
resource.WaitingList.Remove(resource.WaitingList.First(x => x.Key.Equals(process)));
process.StatusList = null;
}
// else remove process from ready list
else
{
ReadyList[(int)process.Priority].Remove(process);
}
// Release resources
foreach (var resourceRequest in process.OtherResources.ToList())
{
var units = resourceRequest.Value;
var resource = resourceRequest.Key;
ReleaseResource(process, resource, units);
}
}
