c# - Is creating tasks via a for loop different to creating them individually? -

the problem having seems related task creation. after using loop populate task array, , starting them within separate loop, results, although consistent, wrong. however, if populate array individually, start each task within loop, fine. can 1 offer me advice?

for example, problematic:

int c = 1; (int = 1; <= 4; i++)     {        taskarray[i-1] = new task(() => calculaterows(c, true));        c = c + 2;     } foreach (task t in taskarray) t.start(); 

but works fine:

taskarray[0] = new task(() => calculaterows(1, true)); taskarray[1] = new task(() => calculaterows(3, true)); taskarray[2] = new task(() => calculaterows(5, true)); taskarray[3] = new task(() => calculaterows(7, true)); foreach (task t in taskarray) t.start(); 

the problem lambda expression captures c - variable c, not value @ time of task creation. time start tasks, c 9. if started them within loop, there's still no guarantee code in lambda expression start execute before change c.

to fix this, can use separate local variable each iteration of loop:

int c = 1; (int = 1; <= 4; i++) {     int temp = c;     taskarray[i-1] = new task(() => calculaterows(temp, true));     c = c + 2; } foreach (task t in taskarray) {     t.start(); } 

or bypass c entirely , compute temp i:

for (int = 1; <= 4; i++) {     int temp = * 2 - 1;     taskarray[i-1] = new task(() => calculaterows(temp, true)); } foreach (task t in taskarray) {     t.start(); } 

do need these separate tasks though? use parallel.for instead? or perhaps enumerable.range suggested in comments:

var tasks = enumerable.range(1, 4)                       .select(x => new task(() => calculaterows(x * 2 - 1, true)                       .toarray(); foreach (task t in tasks) {     t.start(); }