Interrupt Flag - CLI

CLI

This section is about the x86 instruction. For other uses, see CLI.

CLI is commonly used as a synchronization mechanism in uniprocessor systems. For example, a CLI is used in operating systems to disable interrupts so kernel code (typically a driver) can avoid race conditions with an interrupt handler. Note that CLI only affects the interrupt flag for the processor on which it is executed; in multiprocessor systems, executing a CLI instruction does not disable interrupts on other processors. Thus, a driver/interrupt handler race condition can still occur because other processors may service interrupts and execute the offending interrupt handler. For these systems, other synchronization mechanisms such as locks must be used in addition to CLI/STI to prevent all race conditions.

Because the HLT instruction halts until an interrupt occurs, the combination of a CLI followed by a HLT is commonly used to intentionally hang the computer.