Enum ProcessState 

#[non_exhaustive]
pub enum ProcessState {
    Alive,
    Exited,
    Unknown,
}

What the OS can establish about a PID.

Unknown is its own state because the two useful answers need proof in opposite directions. Retiring a process’s work needs proof it exited; treating it as still serving needs proof it runs. A denied or failed query proves neither, and a caller that folds it into either side eventually acts on a guess: waiting forever for a process that is gone, or starting a second owner next to one that is not.

Alive is about a PID, not a program: a PID is reused once its process is gone, on Unix and on Windows alike, so a PID that reads as alive may belong to an unrelated process by now. Before treating it as the daemon you started, confirm through its endpoint (connect and check the peer). To follow one process rather than a PID, keep a ProcessHandle.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Alive

A process with this PID exists and has not exited. It may be a different process from the one that first had the PID.

Exited

The process exited, or no process has this PID any more.

Unknown

The OS did not say, for example because access to the process was denied. Neither alive nor exited can be assumed.

Trait Implementations

impl Clone for ProcessState

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for ProcessState

impl Debug for ProcessState

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for ProcessState

impl PartialEq for ProcessState

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for ProcessState