fixes #5091; Ensure we don't wait on an exited process on Linux (#23743)

Fixes #5091.

Ensure we don't wait on an exited process on Linux

(cherry picked from commit 288d5c4ac3)

lib/pure/osproc.nim

@@ -1416,6 +1416,8 @@ elif not defined(useNimRtl):
           tmspec.tv_nsec = (timeout * 1_000_000)
 
         try:
+          if not running(p):
+            return exitStatusLikeShell(p.exitStatus)
           if clock_gettime(CLOCK_REALTIME, stspec) == -1:
             raiseOSError(osLastError())
           while true:

tests/osproc/twaitforexit.nim

@@ -0,0 +1,18 @@
+import std/[osproc, os, times]
+
+block: # bug #5091
+    when defined(linux):
+        const filename = "false"
+        var p = startProcess(filename, options = {poStdErrToStdOut, poUsePath})
+        os.sleep(1000) # make sure process has exited already
+
+        let atStart = getTime()
+        const msWait = 2000
+
+        try:
+            discard waitForExit(p, msWait)
+        except OSError:
+            discard
+
+        # check that we don't have to wait msWait milliseconds
+        doAssert(getTime() <  atStart + milliseconds(msWait))