sleepinginterruptible

The term sleepinginterruptible (often described in practice as interruptible sleep) refers to a thread or process that is currently asleep but can be woke up by external events, such as signals. In many Unix-like systems, this state corresponds to the kernel’s interruptible sleep condition, allowing a sleeping task to be interrupted so it can handle a signal and resume execution.

In an interruptible sleep, a process typically waits for a condition such as I/O readiness, a timer expiration, or another event, while remaining sensitive to signals. If a signal is delivered, the process transitions to a runnable state, enabling immediate handling of the signal. This behavior supports responsive system design by permitting timely interrupt handling even while resources are waiting on external conditions.

The alternative sleep state is uninterruptible sleep, in which a process cannot be awakened by signals and must wait for the awaited event to complete. This distinction matters for system performance and debugging: interruptible sleep supports responsiveness to signals, while uninterruptible sleep can indicate operations that are blocked on essential I/O and may cause hangs if the event never completes.

In user space, calls that cause blocking waits—such as sleep, nanosleep, select, and poll—may place a thread in an interruptible sleep. If a signal interrupts the wait, these calls often return early with an error such as EINTR, allowing the program to respond to the signal.

Process monitoring tools reflect this state; for example, in Linux, a sleeping interruptible process is shown with a state of 'S' in ps and top, whereas 'D' indicates uninterruptible sleep. Understanding sleepinginterruptible aids in diagnosing latency, responsiveness, and I/O wait issues.