MisterBlonde on 07 December 2008
@jlauro
A function call is single assembly instruction.
Scheduling a thread for execution requires determining which thread from the pool to schedule time (Threads have different priorities, different states). Additionally the scheduler would have to preempt currently running threads, save their context (state of the CPU registers at the time the thread was interrupted), and then load the context into registers from the thread that is getting scheduled for execution.
Certainly all that stuff could possibly be optimized more in the future, but nevertheless it will always be a lot more expensive than a single function call. The more threads and cores the scheduler has to deal with the more complex it becomes and the more often it happens.
