From b2bf948a00b582573fa5a3819fa04fac6977a608 Mon Sep 17 00:00:00 2001
From: Christopher Baines <mail@cbaines.net>
Date: Fri, 17 Nov 2023 12:32:14 +0000
Subject: [PATCH] Add more exception handling to make-resource-pool

As I'm not sure it's working reliably.
---
 guix-data-service/utils.scm | 174 +++++++++++++++++++-----------------
 1 file changed, 92 insertions(+), 82 deletions(-)

diff --git a/guix-data-service/utils.scm b/guix-data-service/utils.scm
index 9dd94df..7357a40 100644
--- a/guix-data-service/utils.scm
+++ b/guix-data-service/utils.scm
@@ -99,94 +99,104 @@
   (let ((channel (make-channel)))
     (spawn-fiber
      (lambda ()
-       (let loop ((resources '())
-                  (available '())
-                  (waiters '()))
+       (while #t
+         (with-exception-handler
+             (lambda (exn)
+               (simple-format
+                (current-error-port)
+                "exception in the ~A pool fiber: ~A\n"
+                name
+                exn))
+           (lambda ()
+             (let loop ((resources '())
+                        (available '())
+                        (waiters '()))
 
-         (match (get-message channel)
-           (('checkout reply)
-            (if (null? available)
-                (if (= (length resources) max-size)
-                    (loop resources
-                          available
-                          (cons reply waiters))
-                    (let ((new-resource (initializer/safe)))
-                      (if new-resource
-                          (let ((checkout-success?
-                                 (perform-operation
-                                  (choice-operation
-                                   (wrap-operation
-                                    (put-operation reply new-resource)
-                                    (const #t))
-                                   (wrap-operation (sleep-operation 0.2)
-                                                   (const #f))))))
-                            (loop (cons new-resource resources)
-                                  (if checkout-success?
-                                      available
-                                      (cons new-resource available))
-                                  waiters))
+               (match (get-message channel)
+                 (('checkout reply)
+                  (if (null? available)
+                      (if (= (length resources) max-size)
                           (loop resources
                                 available
-                                (cons reply waiters)))))
-                (let ((checkout-success?
-                       (perform-operation
-                        (choice-operation
-                         (wrap-operation
-                          (put-operation reply (car available))
-                          (const #t))
-                         (wrap-operation (sleep-operation 0.2)
-                                         (const #f))))))
-                  (if checkout-success?
-                      (loop resources
-                            (cdr available)
-                            waiters)
-                      (loop resources
-                            available
-                            waiters)))))
-           (('return resource)
-            ;; When a resource is returned, prompt all the waiters to request
-            ;; again.  This is to avoid the pool waiting on channels that may
-            ;; be dead.
-            (for-each
-             (lambda (waiter)
-               (spawn-fiber
-                (lambda ()
-                  (perform-operation
-                   (choice-operation
-                    (put-operation waiter 'resource-pool-retry-checkout)
-                    (sleep-operation 0.2))))))
-             waiters)
+                                (cons reply waiters))
+                          (let ((new-resource (initializer/safe)))
+                            (if new-resource
+                                (let ((checkout-success?
+                                       (perform-operation
+                                        (choice-operation
+                                         (wrap-operation
+                                          (put-operation reply new-resource)
+                                          (const #t))
+                                         (wrap-operation (sleep-operation 0.2)
+                                                         (const #f))))))
+                                  (loop (cons new-resource resources)
+                                        (if checkout-success?
+                                            available
+                                            (cons new-resource available))
+                                        waiters))
+                                (loop resources
+                                      available
+                                      (cons reply waiters)))))
+                      (let ((checkout-success?
+                             (perform-operation
+                              (choice-operation
+                               (wrap-operation
+                                (put-operation reply (car available))
+                                (const #t))
+                               (wrap-operation (sleep-operation 0.2)
+                                               (const #f))))))
+                        (if checkout-success?
+                            (loop resources
+                                  (cdr available)
+                                  waiters)
+                            (loop resources
+                                  available
+                                  waiters)))))
+                 (('return resource)
+                  ;; When a resource is returned, prompt all the waiters to request
+                  ;; again.  This is to avoid the pool waiting on channels that may
+                  ;; be dead.
+                  (for-each
+                   (lambda (waiter)
+                     (spawn-fiber
+                      (lambda ()
+                        (perform-operation
+                         (choice-operation
+                          (put-operation waiter 'resource-pool-retry-checkout)
+                          (sleep-operation 0.2))))))
+                   waiters)
 
-            (loop resources
-                  (cons resource available)
-                  ;; clear waiters, as they've been notified
-                  '()))
-           (('stats reply)
-            (let ((stats
-                   `((resources . ,(length resources))
-                     (available . ,(length available))
-                     (waiters   . ,(length waiters)))))
+                  (loop resources
+                        (cons resource available)
+                        ;; clear waiters, as they've been notified
+                        '()))
+                 (('stats reply)
+                  (let ((stats
+                         `((resources . ,(length resources))
+                           (available . ,(length available))
+                           (waiters   . ,(length waiters)))))
 
-              (perform-operation
-               (choice-operation
-                (wrap-operation
-                 (put-operation reply stats)
-                 (const #t))
-                (wrap-operation (sleep-operation 0.2)
-                                (const #f)))))
+                    (perform-operation
+                     (choice-operation
+                      (wrap-operation
+                       (put-operation reply stats)
+                       (const #t))
+                      (wrap-operation (sleep-operation 0.2)
+                                      (const #f)))))
 
-            (loop resources
-                  available
-                  waiters))
-           (unknown
-            (simple-format
-             (current-error-port)
-             "unrecognised message to ~A resource pool channel: ~A\n"
-             name
-             unknown)
-            (loop resources
-                  available
-                  waiters))))))
+                  (loop resources
+                        available
+                        waiters))
+                 (unknown
+                  (simple-format
+                   (current-error-port)
+                   "unrecognised message to ~A resource pool channel: ~A\n"
+                   name
+                   unknown)
+                  (loop resources
+                        available
+                        waiters)))))
+           #:unwind? #t))))
 
     channel))