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Assign passed functions result to object with variable type in C#

For an integration I'm running as a service once a day, I need to assign the result of API-calls to local variables. However, those API's might at any time decide to throw a 401 error, in which case I just want to try again, up to three times.
I've got a functioning code to do that:
List<APIEntityProject> projectList = null;
private bool SetProjectList(){
const maxRetries = 3;
const RetryPause = 3000;
int retries = 0;
do
{
try
{
projectList = ProjApi.GetProject(activeWorkspace.WorkspaceCode);
}
catch (ApiException e)
{
if (e.ErrorCode == 401) // Unauthorized error (e.g. user doesn't have access to this Workspace
{
Log.Warning("Unauthorized error while fetching projects from Workspace, try {retries}",retries);
retries++;
System.Threading.Thread.Sleep(RetryPause * retries);//Waits 3 and then 6 seconds before retrying.
}
else throw;
}
} while (projectList == null || retries < maxRetries);
if (retries == maxRetries)
{
Log.Error("An error has occured while trying to retrieve affected Projects, skipped document");
errorCount++;
return false;
}
return true;
}
But unfortunately I need to replicate this Logic so often I would like to use it in a function e.g. RetryNTimes (similar to This Solution
List<APIEntityProject> projectList = null;
List<APIEntityWBS> WBSList = null;
List<APIEntitySopeItem> SIList = null;
List<APIEntityScopeAsignment> SAList = null;
List<APIEntityActivity> ActList = null;
...
RetryNTimes(projectList,ProjApi.GetProject(activeWorkspace.WorkspaceCode),3,3000,"ProjectList");
RetryNTimes(WBSList, WBSApi.GetAllWBS(activeProject.ProjectID),3,3000,"WBSList");
RetryNTimes(SIList, SIApi.GetAllScopeItems(activeProject.ProjectID),3,3000,"ScopeItemsList");
RetryNTimes(SAList, SAApi.GetAllScopeAssignments(activeProject.ProjectID),3,3000,"ScopeAssignmentsList");
RetryNTimes(ActList, ActApi.GetAllActivities(activeProject.ProjectID),3,3000,"ActivityList");
...
private bool RetryNTimes(T object, Func<T> func, int times, int WaitInterval, string etext){
do
{
try
{
object = func();
}
catch (ApiException e)
{
if (e.ErrorCode == 401)
{
retries++;
Log.Warning("Unauthorized error while fetching {APIErrorSubject}, try {retries}",eText,retries);
System.Threading.Thread.Sleep(RetryPause * retries);//Waits 3 and then 6 seconds before retrying.
}
else throw;
}
} while (object == null || retries < maxRetries);
if (retries == maxRetries)
{
Log.Error("An error has occured while trying to retrieve {APIErrorSubject}, skipped document",eText);
errorCount++;
return false;
}
return true;
}
I've also read through typedef and function pointers but I'm not sure if it's possible to do with variable types.
Any Ideas?

That article refers to C language. In C# you can use delegates. Here's a link to start you off.

Based on the idea of asawyer and by looking through some other examples of delegates I've been able to make it work.
static T2 TryNTimes<T1,T2>(Func<T1,T2> func,T1 obj, int times, int WaitInterval)
{
while (times > 0)
{
try
{
T2 result = func.Invoke(obj);
return result;
}
catch (Exception e)
{
if (--times <= 0)
throw;
System.Threading.Thread.Sleep(WaitInterval * times);
}
}
return default;
}
Now I need only 2 steps in my main function
activeWorkspace = TryNTimes(WrkApi.WorkspaceCodeWorkspaceCodeFindByName17, ServiceSettings.sqlConnection.Workspace, 3, 3000)[0];
ProjectList = TryNTimes(WrkApi.GetProjectsByWorkspaceCode, activeWorkspace.code, 3, 3000);
The first one can still generate an error as the default List is empty and you can't take 0th element then. But I guess I can find another way around that issue.

Sqlite atomic operations

I run 5 applications which are using the same sqlite database (each application is different process). Unfortunately operations like GetEmptyPort have to be atomic to prevent returning same values. Right now I achieve that by using system Mutex, but I dont like this solution. Is there any built-in solution to do this in pure sqlite?
This is my code:
private static Mutex DB_MUTEX = new Mutex(false, "FOO_DB_MUTEX");
private T OnMutexWork<T>(Func<T> func)
{
try
{
DB_MUTEX.WaitOne();
return func.Invoke();
}
catch (Exception ex)
{
throw;
}
finally
{
DB_MUTEX.ReleaseMutex();
}
}
private SQLiteConnection GetConnection()
{
return new SQLiteConnection(databasePath);
}
private int GetEmptyPort(int min, int max)
{
return OnMutexWork<int>(() =>
{
using (var conn = GetConnection())
{
var allPorts = conn.Table<Port>()
.ToList();
for (int i = min; i <= max; i++)
{
if (!allPorts.Any(x => x.Value == i))
{
var item = new Port() { Value = i};
conn.Insert(item);
return i;
}
}
throw new Exception("Couldn't find empty port");
}
});
}
I tried what #Shawn Suggested:
private int GetEmptyPort(int min, int max)
{
using (var conn = GetConnection())
{
conn.RunInTransaction(() =>
{
var allPorts = conn.Table<Port>()
.ToList();
for (int i = min; i <= max; i++)
{
if (!allPorts.Any(x => x.Value == i))
{
var item = new Port() { Value = i};
conn.Insert(item);
return i;
}
}
});
throw new Exception("Couldn't find empty port");
}
}
But I am getting SQLite.SQLiteException: 'Busy' error when accessing database from different connections.

c# - Waiting for 1 of 2 threads to be finished

I have a place in my code, that I need to wait for a either finger to be identified on a sensor, or the user pressed a key to abort this action and return to the main menu.
I tried using something like conditional variables with Monitor and lock concepts but when I try to alert the main thread, nothing happens.
CODE:
private static object _syncFinger = new object(); // used for syncing
private static bool AttemptIdentify()
{
// waiting for either the user cancels or a finger is inserted
lock (_syncFinger)
{
Thread tEscape = new Thread(new ThreadStart(HandleIdentifyEscape));
Thread tIdentify = new Thread(new ThreadStart(HandleIdentify));
tEscape.IsBackground = false;
tIdentify.IsBackground = false;
tEscape.Start();
tIdentify.Start();
Monitor.Wait(_syncFinger); // -> Wait part
}
// Checking the change in the locked object
if (_syncFinger is FingerData) // checking for identity found
{
Console.WriteLine("Identity: {0}", ((FingerData)_syncFinger).Guid.ToString());
}
else if(!(_syncFinger is Char)) // char - pressed a key to return
{
return false; // returns with no error
}
return true;
}
private static void HandleIdentifyEscape()
{
do
{
Console.Write("Enter 'c' to cancel: ");
} while (Console.ReadKey().Key != ConsoleKey.C);
_syncFinger = new Char();
LockNotify((object)_syncFinger);
}
private static void HandleIdentify()
{
WinBioIdentity temp = null;
do
{
Console.WriteLine("Enter your finger.");
try // trying to indentify
{
temp = Fingerprint.Identify(); // returns FingerData type
}
catch (Exception ex)
{
Console.WriteLine("ERROR: " + ex.Message);
}
// if couldn't identify, temp would stay null
if(temp == null)
{
Console.Write("Invalid, ");
}
} while (temp == null);
_syncFinger = temp;
LockNotify(_syncFinger);
}
private static void LockNotify(object syncObject)
{
lock(syncObject)
{
Monitor.Pulse(syncObject);
}
}

when i try to alert the main thread, nothing happens.
That's because the main thread is waiting on the monitor for the object created here:
private static object _syncFinger = new object(); // used for syncing
But each of your threads replaces that object value, and then signals the monitor for the new object. The main thread has no knowledge of the new object, and so of course signaling the monitor for that new object will have no effect on the main thread.
First, any time you create an object for the purpose of using with lock, make it readonly:
private static readonly object _syncFinger = new object(); // used for syncing
It's always the right thing to do , and that will prevent you from ever making the mistake of changing the monitored object while a thread is waiting on it.
Next, create a separate field to hold the WinBioIdentity value, e.g.:
private static WinBioIdentity _syncIdentity;
And use that to relay the result back to the main thread:
private static bool AttemptIdentify()
{
// waiting for either the user cancels or a finger is inserted
lock (_syncFinger)
{
_syncIdentity = null;
Thread tEscape = new Thread(new ThreadStart(HandleIdentifyEscape));
Thread tIdentify = new Thread(new ThreadStart(HandleIdentify));
tEscape.IsBackground = false;
tIdentify.IsBackground = false;
tEscape.Start();
tIdentify.Start();
Monitor.Wait(_syncFinger); // -> Wait part
}
// Checking the change in the locked object
if (_syncIdentity != null) // checking for identity found
{
Console.WriteLine("Identity: {0}", ((FingerData)_syncIdentity).Guid.ToString());
return true;
}
return false; // returns with no error
}
private static void HandleIdentifyEscape()
{
do
{
Console.Write("Enter 'c' to cancel: ");
} while (Console.ReadKey().Key != ConsoleKey.C);
LockNotify((object)_syncFinger);
}
private static void HandleIdentify()
{
WinBioIdentity temp = null;
do
{
Console.WriteLine("Enter your finger.");
try // trying to indentify
{
temp = Fingerprint.Identify(); // returns FingerData type
}
catch (Exception ex)
{
Console.WriteLine("ERROR: " + ex.Message);
}
// if couldn't identify, temp would stay null
if(temp == null)
{
Console.Write("Invalid, ");
}
} while (temp == null);
__syncIdentity = temp;
LockNotify(_syncFinger);
}
All that said, you should prefer to use the modern async/await idiom for this:
private static bool AttemptIdentify()
{
Task<WinBioIdentity> fingerTask = Task.Run(HandleIdentify);
Task cancelTask = Task.Run(HandleIdentifyEscape);
if (Task.WaitAny(fingerTask, cancelTask) == 0)
{
Console.WriteLine("Identity: {0}", fingerTask.Result.Guid);
return true;
}
return false;
}
private static void HandleIdentifyEscape()
{
do
{
Console.Write("Enter 'c' to cancel: ");
} while (Console.ReadKey().Key != ConsoleKey.C);
}
private static WinBioIdentity HandleIdentify()
{
WinBioIdentity temp = null;
do
{
Console.WriteLine("Enter your finger.");
try // trying to indentify
{
temp = Fingerprint.Identify(); // returns FingerData type
}
catch (Exception ex)
{
Console.WriteLine("ERROR: " + ex.Message);
}
// if couldn't identify, temp would stay null
if(temp == null)
{
Console.Write("Invalid, ");
}
} while (temp == null);
return temp;
}
The above is a bare-minimum example. It would be better to make the AttemptIdentify() method async itself, and then use await Task.WhenAny() instead of Task.WaitAny(). It would also be better to include some mechanism to interrupt the tasks, i.e. once one has completed, you should want to interrupt the other so it's not lying around continuing to attempt its work.
But those kinds of issues are not unique to the async/await version, and don't need to be solved to improve on the code you have now.

using do-while and skipping the next lines

I want to run a method _doing() that loops infinitely until a shutdownEvent is triggered. This is basically executed/started on a new Thread(). But I need not _doSomething if it is true somewhere. what should i do after if (_doSomething)? Code snippet below. Thanks.
private HighResolutionLapseTimer _lapseTimer;
private int _timeToNext
{
get
{
int lapseTime = _lapseTimer.LapseTime();
int next = DO_PERIOD - lapseTime;
if (next > 0)
{
return next;
}
else
{
return 1;
}
}
}
int DO_PERIOD = 60000;
private void _doing()
{
int _nextDoing = DO_PERIOD;
Thread.Sleep(_nextDoing);
do
{
LogInfo("Starting _doing");
lock (this)
{
if (_doSomething)
{
// skip this time because we are currently archiving
}
_doSomething = true;
}
try
{
_lapseTimer.Start();
DoSomethingHere(); //takes long processing
}
catch (Exception ex)
{
LogException(ex);
}
finally
{
lock (this)
{
_nextDoing = (int)_timeToNext;
_doSomething = false;
}
}
} while (!shutdownWaitHandle.WaitOne(_nextDoing, false));
LogInfo("Stopping _doing");
}

You could use the continue; statement.

Ohw! I just realized that a do-while is similar to a while. And to 'skip' the execution, you just have to use the continue; if the if statement is true

How can I pass variable to Action?

below is the code sample, I want the components in the queue to take the local variable "entity", how can I achive this? thx
private void DoComparison(StuffEntity entity)
{
try
{
bool dataFlag = CheckIsNewData(entity.PickingTime, entity.WarningPeriod);
if (dataFlag)
{
Queue<Action<StuffEntity>> queue = new Queue<Action<StuffEntity>>();
//How can I let the queue stuff take the entity?
queue.Enqueue(DelaySendingMessageOut);
if (!QueueItem.ContainsKey(entity.FridgeID))
{
QueueItem.Add(entity.FridgeID, queue);
}
}
}
catch (Exception ex)
{
CommonUnity.WriteLog(ex.Message);
CommonUnity.WriteLog(ex.StackTrace);
}
}
private void DelaySendingMessageOut(StuffEntity entity)
{
int pendingPeroid = entity.PendingTime.ToInt();
if (pendingPeroid <= 0)
pendingPeroid = 5;
Thread.Sleep(pendingPeroid * 60 * 1000);
TriggerCheckingBeforeSendMessageOut(entity);
}

queue.Enqueue((e) => DelaySendingMessageOut(entity));
But you can use Queue<Action> since you will not use the argument e:
Queue<Action> queue = new Queue<Action>();
queue.Enqueue(() => DelaySendingMessageOut(entity));