c# - ParallelFor not cancelling all threads immediately if condition met -

code waits until running tasks have finished before operationcancelledexception thrown.

i program stop on condition being true.

static void main() {     // want break out of parallel.for when condition occurs     var cts = new cancellationtokensource();     var po = new paralleloptions();     po.cancellationtoken = cts.token;      long countertotal = 0;      try     {         // want have sum of counts @ end         parallel.for<long>(1, 26, po, () => 0, delegate(int i, parallelloopstate state, long countersubtotal)                 {                     po.cancellationtoken.throwifcancellationrequested();                     console.writeline(i.tostring());                      (int k = 0; k < 1000000000; k++)                     {                         countersubtotal++;                          if (i == 4 && k == 900000000)                         {                             cts.cancel();                             // break out here                         }                     }                      return countersubtotal;                 }, (x) => interlocked.add(ref countertotal, x)             );     }     catch (operationcanceledexception e)     {         console.writeline("cancelled");         console.writeline("total iterations across threads {0}", string.format("{0:n0}", countertotal));         console.readline();     } } 

i found putting breakpoint on cts.cancel() , in catch demonstrates happening.

have looked @ state.stop too.

this simplified version of other code.

perhaps parallel.for isn't ideal things long running inside method if want break out immediately.

update2: code works expected , gives total

static void main() {     // want break out of parallel.for when condition occurs     var cts = new cancellationtokensource();     var po = new paralleloptions();     po.cancellationtoken = cts.token;      long countertotal = 0;      try     {         // want have sum of counts @ end         // using type param here make countersubtotal long         parallel.for<long>(1, 26, po, () => 0, delegate(int i, parallelloopstate state, long countersubtotal)                 {                     console.writeline(i.tostring());                     // 1 billion                     (int k = 0; k < 1000000000; k++)                     {                         //po.cancellationtoken.throwifcancellationrequested();                         if (po.cancellationtoken.iscancellationrequested)                         {                             return countersubtotal;                         }                         countersubtotal++;                          if (i == 4 && k == 400000000)                         {                             console.writeline("inner cancelled");                             cts.cancel();                         }                     }                     return countersubtotal;                 }, (x) => interlocked.add(ref countertotal, x)             );     }     catch (operationcanceledexception e)     {         console.writeline("cancelled");         console.writeline("total iterations across threads {0}", string.format("{0:n0}", countertotal));         console.readline();     } } 

if want break more "immediately" need check cancellation token inside of inner for. now, check cancel before entering, after won't @ token again.

for (int k = 0; k < 1000000000; k++) {     po.cancellationtoken.throwifcancellationrequested();     countersubtotal++;      if (i == 4 && k == 900000000)     {        cts.cancel();      } }