Editing Busy waiting (section)

== Alternatives ==
Most operating systems and threading libraries provide a variety of [[system call]]s that will [[Process states#Blocked|block]] the process on an event, such as lock acquisition, timer changes, [[I/O]] availability or [[signal (computing)|signals]].   Using such calls generally produces the simplest, most efficient, fair, and [[race condition|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 [[Resource starvation|starvation]].

Busy-waiting itself can be made much less wasteful by using a delay function (e.g., <code>[[sleep()]]</code>) 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 (such as operating systems), infinite busy waiting can be implemented by using unconditional jumps as shown by this [[Netwide Assembler|NASM]] syntax: <kbd>jmp $</kbd>. The CPU will unconditionally [[JMP (x86 instruction)|jump]] to its [[program counter|own position]] forever. A busy wait like this can be replaced with:
<syntaxhighlight lang="asm">
sleep:
hlt
jmp sleep
</syntaxhighlight>

For more information, see [[HLT (x86 instruction)]].