Busy Waiting - Busy-waiting Alternatives

Busy-waiting Alternatives

Most operating systems and threading libraries provide a variety of system calls that will block the process on an event, such as lock acquisition, timer changes, I/O availability or signals. Using such calls generally produces the simplest, most efficient, fair, and race-free result. A single call checks, informs the scheduler of the event it is waiting for, inserts a memory barrier where applicable, and may perform a requested I/O operation before returning. Other processes can use the CPU while the caller is blocked. The scheduler is given the information needed to implement priority inheritance or other mechanisms to avoid starvation.

Busy-waiting itself can be made much less wasteful by using a delay function (e.g., sleep) found in most operating systems. This puts a thread to sleep for a specified time, during which the thread will waste no CPU time. If the loop is checking something simple then it will spend most of its time asleep and will waste very little CPU time.

In programs that never end (i.e. OS'es), infinite busy waiting can be implemented by using i.e. this NASM syntax: jmp $. The CPU will unconditionally jump to its own position forever. A busy wait like this can be replaced with:

For more information, see hlt.