c# - Mysterious Negative Counter Value -

i'm creating new threads every sql call project. there millions of sql calls i'm calling procedure in new thread handle sql calls.

in doing so, wanted increment , decrement counter know when these threads have completed sql query.

to amazement output shows negative values in counter. how? when starting 0 , adding 1 @ beginning of process , subtracting 1 @ end of process?

this int not called anywhere else in program.. following code..

public static int counter=0;  while(!txtstream.endofstream) {     new thread(delegate()     {         processline();     }).start();     console.writeline(counter); }  public static void processline() {     counter++;     sql.executenonquery();     counter--; } 

output looks this:

1 21 -2 -2 5 

nothing mysterious it, using threading, right?

the ++ , -- operator aren't thread safe. this.

public static void processline() {     interlocked.increment(ref counter);     sql.executenonquery();     interlocked.decrement(ref counter); }