Don't consider Zombies to be alive

This fixes a regression that was introduced in #171

Closes #197

(cherry picked from commit 20b1182)

src/process/mod.rs

@@ -850,8 +850,14 @@ impl Process {
     }
 
     /// Is this process still alive?
+    /// 
+    /// Processes in the Zombie or Dead state are not considered alive.
     pub fn is_alive(&self) -> bool {
-        rustix::fs::statat(&self.fd, "stat", AtFlags::empty()).is_ok()
+        if let Ok(stat) = self.stat() {
+            stat.state != 'Z' && stat.state != 'X'
+        } else {
+            false
+        }
     }
 
     /// What user owns this process?

src/process/tests.rs

@@ -204,6 +204,25 @@ fn test_smaps() {
 fn test_proc_alive() {
     let myself = Process::myself().unwrap();
     assert!(myself.is_alive());
+
+    // zombies should not be considered alive
+    let mut command = std::process::Command::new("sleep");
+    command
+        .arg("0")
+        .stdout(std::process::Stdio::null())
+        .stderr(std::process::Stdio::null());
+    let mut child = command.spawn().unwrap();
+    let child_pid = child.id() as i32;
+
+    // sleep very briefly to allow the child to start and then exit
+    std::thread::sleep(std::time::Duration::from_millis(20));
+
+    let child_proc = Process::new(child_pid).unwrap();
+    assert!(!child_proc.is_alive(), "Child state is: {:?}", child_proc.stat());
+    assert!(child_proc.stat().unwrap().state().unwrap() == ProcState::Zombie);
+    child.wait().unwrap();
+    assert!(Process::new(child_pid).is_err());
+    assert!(!child_proc.is_alive(), "Child state is: {:?}", child_proc.stat());
 }
 
 #[test]