c# - Wait for Collection to be Updated -

i need bit of code wait item added collection. thread needs wait until completes before continues. item gets added collection thread (kicked off elsewhere), , have no way signal current thread has occurred.

a naive implementation might (ignoring thread safety on collection, etc. now):

public static list<string> mylist = new list<string>();  public void waitingmethod(string id) {     bool waiting = true;     while (waiting)     {         int index = mylist.indexof(id);         if (index >= 0)         {             waiting = false;         }     }      //thread continues here } 

i believe block thread , peg processor.

what more efficient way achieve this?

could instead use observable collection, , subscribe collectionchanged event?

namespace consoleapplication3 {     using system;     using system.collections.objectmodel;     using system.linq;     using system.threading;     using system.threading.tasks;      internal class program     {         private static readonly observablecollection<string> mylist = new observablecollection<string>();          private static autoresetevent resetevent = new autoresetevent(false);         private static void main(string[] args)         {             task.factory.startnew(                 () =>                 {                     (int = 0; < 10; i++)                     {                         string item = i.tostring("0000");                         mylist.add(item);                         console.writeline(item);                         thread.sleep(1000);                     }                 });              mylist.collectionchanged += (sender, eventargs) =>             { if (eventargs.newitems.cast<string>().any(a => a.equals("0005"))) resetevent.set(); };             resetevent.waitone();         }      }  } 

here how can control loop generating items being added collection:

namespace consoleapplication3 {     using system;     using system.collections.objectmodel;     using system.linq;     using system.threading;     using system.threading.tasks;      internal class program     {         #region static fields          private static readonly cancellationtokensource cts = new cancellationtokensource();          private static readonly observablecollection<string> mylist = new observablecollection<string>();          private static readonly autoresetevent resetevent = new autoresetevent(false);          #endregion          #region methods          private static void main(string[] args)         {             task task = task.factory.startnew(                 () =>                 {                     (int = 0; < 10 && !cts.iscancellationrequested; i++)                     {                         string item = i.tostring("0000");                         mylist.add(item);                         console.writeline(item);                         thread.sleep(100);                     }                 },                 cts.token);             task finish = task.continuewith(antecedent => { console.writeline("task finished. status {0}", antecedent.status); });             mylist.collectionchanged += (sender, eventargs) =>             {                 if (eventargs.newitems.cast<string>().any(a => a.equals("0005")))                 {                     cts.cancel();                     resetevent.set();                 }             };             resetevent.waitone();             task.waitall(finish);         }          #endregion     } }