Review abnormal termination code path.

In case of an exceptional condition leading to termination of the pgloader
program we tried to use log-message after the monitor should have been
closed. Also the 0.3s delay to let latests messages out looks like a poor
design.

This patch attempts to remedy both the situation: refrain from using a
closed down monitoring thread, and properly wait until it's done before
returning to the shell.

See #583.

src/main.lisp

@@ -345,13 +345,17 @@
 
               (source-definition-error (c)
                 (declare (ignore c))    ; handler-bind printed it out
-                (sleep 0.3)             ; wait until monitor stops...
+                ;; wait until monitor stops...
+                (let ((lp:*kernel* *monitoring-kernel*))
+                  (lp:end-kernel :wait t))
                 (uiop:quit +os-code-error-bad-source+))
 
               (condition (c)
                 (declare (ignore c))    ; handler-bind printed it out
-                (log-message :log "What I am doing here?")
-                (sleep 0.3)             ; wait until monitor stops...
+                (format *error-output* "~%What I am doing here?~%~%")
+                ;; wait until monitor stops...
+                (let ((lp:*kernel* *monitoring-kernel*))
+                  (lp:end-kernel :wait t))
                 (uiop:quit +os-code-error+)))))
 
         ;; done.

src/package.lisp

@@ -220,6 +220,7 @@
 (defpackage #:pgloader.monitor
   (:use #:cl #:pgloader.params #:pgloader.state)
   (:export #:with-monitor
+           #:*monitoring-kernel*
            #:*monitoring-queue*
            #:log-message
            #:new-label

src/utils/monitor.lisp

@@ -12,6 +12,9 @@
 ;;;
 (in-package :pgloader.monitor)
 
+(defvar *monitoring-kernel* nil
+  "Internal lparallel kernel to manage the separate monitor thread.")
+
 (defvar *monitoring-queue* nil
   "Internal lparallel queue where to send and receive messages from.")
 
@@ -130,8 +133,12 @@
                       (*standard-output*     . ,*standard-output*)
                       (*summary-pathname*    . ,*summary-pathname*)
                       (*sections*            . ',*sections*)))
-         (lparallel:*kernel*   (lp:make-kernel 1 :bindings bindings))
-         (*monitoring-channel* (lp:make-channel)))
+         (kernel      (lp:make-kernel 1 :bindings bindings))
+         (lparallel:*kernel* kernel))
+
+    ;; make our kernel and channel visible from the outside
+    (setf *monitoring-kernel* kernel
+          *monitoring-channel* (lp:make-channel))
 
     (lp:submit-task *monitoring-channel* #'monitor *monitoring-queue*)
     (send-event (make-start :start-logger start-logger))