aboutsummaryrefslogtreecommitdiff
path: root/guix-data-service/utils.scm
blob: 6cab90447e070216a389467df161917070030cb7 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
;;; Guix Data Service -- Information about Guix over time
;;; Copyright © 2020 Christopher Baines <mail@cbaines.net>
;;;
;;; This program is free software: you can redistribute it and/or
;;; modify it under the terms of the GNU Affero General Public License
;;; as published by the Free Software Foundation, either version 3 of
;;; the License, or (at your option) any later version.
;;;
;;; This program is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
;;; Affero General Public License for more details.
;;;
;;; You should have received a copy of the GNU Affero General Public
;;; License along with this program.  If not, see
;;; <http://www.gnu.org/licenses/>.

(define-module (guix-data-service utils)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-11)
  #:use-module (ice-9 ftw)
  #:use-module (ice-9 match)
  #:use-module (ice-9 atomic)
  #:use-module (ice-9 format)
  #:use-module (ice-9 threads)
  #:use-module (ice-9 exceptions)
  #:use-module (ice-9 ports internal)
  #:use-module (ice-9 suspendable-ports)
  #:use-module (lzlib)
  #:use-module (fibers)
  #:use-module (fibers channels)
  #:use-module (fibers operations)
  #:use-module (fibers timers)
  #:use-module (fibers conditions)
  #:use-module (fibers scheduler)
  #:use-module (prometheus)
  #:export (call-with-time-logging
            with-time-logging
            prevent-inlining-for-tests

            resource-pool-default-timeout
            make-resource-pool
            destroy-resource-pool
            call-with-resource-from-pool
            with-resource-from-pool
            resource-pool-stats

            parallel-via-fibers
            par-map&
            letpar&

            chunk
            chunk!
            chunk-for-each!

            delete-duplicates/sort!

            get-guix-metrics-updater

            call-with-sigint
            run-server/patched

            spawn-port-monitoring-fiber))

(define (call-with-time-logging action thunk)
  (simple-format #t "debug: Starting ~A\n" action)
  (let ((start-time (current-time)))
    (let-values
        ((result (thunk)))
      (let ((time-taken (- (current-time) start-time)))
        (simple-format #t "debug: Finished ~A, took ~A seconds\n"
                       action time-taken))
      (apply values result))))

(define-syntax-rule (with-time-logging action exp ...)
  "Log under NAME the time taken to evaluate EXP."
  (call-with-time-logging action (lambda () exp ...)))

(define-syntax-rule (prevent-inlining-for-tests var)
  (set! var var))

(define* (make-resource-pool initializer max-size
                             #:key (min-size max-size)
                             (idle-seconds #f)
                             (delay-logger (const #f))
                             (duration-logger (const #f))
                             destructor
                             lifetime
                             (name "unnamed"))
  (define (initializer/safe)
    (with-exception-handler
        (lambda (exn)
          (simple-format
           (current-error-port)
           "exception running ~A resource pool initializer: ~A:\n  ~A\n"
           name
           initializer
           exn)
          #f)
      (lambda ()
        (with-throw-handler #t
          initializer
          (lambda args
            (backtrace))))
      #:unwind? #t))

  (define (destructor/safe args)
    (let ((success?
           (with-exception-handler
               (lambda (exn)
                 (simple-format
                  (current-error-port)
                  "exception running resource pool destructor (~A): ~A:\n  ~A\n"
                  name
                  destructor
                  exn)
                 #f)
             (lambda ()
               (with-throw-handler #t
                 (lambda ()
                   (destructor args)
                   #t)
                 (lambda _
                   (backtrace))))
             #:unwind? #t)))

      (or success?
          #t
          (begin
            (sleep 5)
            (destructor/safe args)))))

  (let ((channel (make-channel))
        (checkout-failure-count 0))
    (spawn-fiber
     (lambda ()
       (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 '())
                        (resources-last-used '()))

               (match (if idle-seconds
                          (perform-operation
                           (choice-operation
                            (get-operation channel)
                            (wrap-operation
                             ;; TODO Do something smarter
                             (sleep-operation 10)
                             (const '(check-for-idle-resources)))))
                          (get-message channel))
                 (('checkout reply)
                  (if (null? available)
                      (if (= (length resources) max-size)
                          (loop resources
                                available
                                (cons reply waiters)
                                resources-last-used)
                          (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 1)
                                                         (const #f))))))
                                  (unless checkout-success?
                                    (set! checkout-failure-count
                                          (+ 1 checkout-failure-count)))

                                  (loop (cons new-resource resources)
                                        (if checkout-success?
                                            available
                                            (cons new-resource available))
                                        waiters
                                        (cons (get-internal-real-time)
                                              resources-last-used)))
                                (loop resources
                                      available
                                      (cons reply waiters)
                                      resources-last-used))))
                      (let ((checkout-success?
                             (perform-operation
                              (choice-operation
                               (wrap-operation
                                (put-operation reply (car available))
                                (const #t))
                               (wrap-operation (sleep-operation 1)
                                               (const #f))))))
                        (unless checkout-success?
                          (set! checkout-failure-count
                                (+ 1 checkout-failure-count)))

                        (if checkout-success?
                            (loop resources
                                  (cdr available)
                                  waiters
                                  resources-last-used)
                            (loop resources
                                  available
                                  waiters
                                  resources-last-used)))))
                 (('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
                        '()
                        (begin
                          (list-set!
                           resources-last-used
                           (list-index (lambda (x)
                                         (eq? x resource))
                                       resources)
                           (get-internal-real-time))
                          resources-last-used)))
                 (('stats reply)
                  (let ((stats
                         `((resources              . ,(length resources))
                           (available              . ,(length available))
                           (waiters                . ,(length waiters))
                           (checkout-failure-count . ,checkout-failure-count))))

                    (perform-operation
                     (choice-operation
                      (wrap-operation
                       (put-operation reply stats)
                       (const #t))
                      (wrap-operation (sleep-operation 0.2)
                                      (const #f)))))

                  (loop resources
                        available
                        waiters
                        resources-last-used))
                 (('check-for-idle-resources)
                  (let* ((resources-last-used-seconds
                          (map
                           (lambda (internal-time)
                             (/ (- (get-internal-real-time) internal-time)
                                internal-time-units-per-second))
                           resources-last-used))
                         (resources-to-destroy
                          (filter-map
                           (lambda (resource last-used-seconds)
                             (if (and (member resource available)
                                      (> last-used-seconds idle-seconds))
                                 resource
                                 #f))
                           resources
                           resources-last-used-seconds)))

                    (for-each
                     (lambda (resource)
                       (destructor/safe resource))
                     resources-to-destroy)

                    (loop (lset-difference eq? resources resources-to-destroy)
                          (lset-difference eq? available resources-to-destroy)
                          waiters
                          (filter-map
                           (lambda (resource last-used)
                             (if (memq resource resources-to-destroy)
                                 #f
                                 last-used))
                           resources
                           resources-last-used))))
                 (('destroy reply)
                  (if (= (length resources) (length available))
                      (begin
                        (for-each
                         (lambda (resource)
                           (destructor/safe resource))
                         resources)
                        (put-message reply 'destroy-success))
                      (begin
                        (spawn-fiber
                         (lambda ()
                           (perform-operation
                            (choice-operation
                             (put-operation reply 'resource-pool-destroy-failed)
                             (sleep-operation 10)))))
                        (loop resources
                              available
                              waiters
                              resources-last-used))))
                 (unknown
                  (simple-format
                   (current-error-port)
                   "unrecognised message to ~A resource pool channel: ~A\n"
                   name
                   unknown)
                  (loop resources
                        available
                        waiters
                        resources-last-used)))))
           #:unwind? #t))))

    channel))

(define (destroy-resource-pool pool)
  (let ((reply (make-channel)))
    (put-message pool (list 'destroy reply))
    (let ((msg (get-message reply)))
      (unless (eq? msg 'destroy-success)
        (error msg)))))

(define resource-pool-default-timeout
  (make-parameter #f))

(define &resource-pool-timeout
  (make-exception-type '&recource-pool-timeout
                       &error
                       '()))

(define make-resource-pool-timeout-error
  (record-constructor &resource-pool-timeout))

(define resource-pool-timeout-error?
  (record-predicate &resource-pool-timeout))

(define* (call-with-resource-from-pool pool proc #:key (timeout 'default))
  "Call PROC with a resource from POOL, blocking until a resource becomes
available.  Return the resource once PROC has returned."

  (define timeout-or-default
    (if (eq? timeout 'default)
        (resource-pool-default-timeout)
        timeout))

  (let ((resource
         (let ((reply (make-channel)))
           (if timeout-or-default
               (let loop ((start-time (get-internal-real-time)))
                 (perform-operation
                  (choice-operation
                   (wrap-operation
                    (put-operation pool `(checkout ,reply))
                    (const #t))
                   (wrap-operation (sleep-operation timeout-or-default)
                                   (const #f))))

                 (let ((time-remaining
                        (- timeout-or-default
                           (/ (- (get-internal-real-time)
                                 start-time)
                              internal-time-units-per-second))))
                   (if (> time-remaining 0)
                       (let ((response
                              (perform-operation
                               (choice-operation
                                (get-operation reply)
                                (wrap-operation (sleep-operation time-remaining)
                                                (const #f))))))
                         (if (or (not response)
                                 (eq? response 'resource-pool-retry-checkout))
                             (if (> (- timeout-or-default
                                       (/ (- (get-internal-real-time)
                                             start-time)
                                          internal-time-units-per-second))
                                    0)
                                 (loop start-time)
                                 #f)
                             response))
                       #f)))
               (let loop ()
                 (put-message pool `(checkout ,reply))
                 (let ((response (get-message reply)))
                   (if (eq? response 'resource-pool-retry-checkout)
                       (loop)
                       response)))))))

    (when (or (not resource)
              (eq? resource 'resource-pool-retry-checkout))
      (raise-exception
       (make-resource-pool-timeout-error)))

    (with-exception-handler
        (lambda (exception)
          (put-message pool `(return ,resource))
          (raise-exception exception))
      (lambda ()
        (call-with-values
            (lambda ()
              (with-throw-handler #t
                (lambda ()
                  (proc resource))
                (lambda _
                  (backtrace))))
          (lambda vals
            (put-message pool `(return ,resource))
            (apply values vals))))
      #:unwind? #t)))

(define-syntax-rule (with-resource-from-pool pool resource exp ...)
  (call-with-resource-from-pool
   pool
   (lambda (resource) exp ...)))

(define* (resource-pool-stats pool #:key (timeout 5))
  (let ((reply (make-channel))
        (start-time (get-internal-real-time)))
    (perform-operation
     (choice-operation
      (wrap-operation
       (put-operation pool `(stats ,reply))
       (const #t))
      (wrap-operation (sleep-operation timeout)
                      (const #f))))

    (let ((time-remaining
           (- timeout
              (/ (- (get-internal-real-time)
                    start-time)
                 internal-time-units-per-second))))
      (if (> time-remaining 0)
          (let ((response
                 (perform-operation
                  (choice-operation
                   (get-operation reply)
                   (wrap-operation (sleep-operation time-remaining)
                                   (const #f))))))
            response)
          (raise-exception
           (make-resource-pool-timeout-error))))))

(define (defer-to-parallel-fiber thunk)
  (let ((reply (make-channel)))
    (spawn-fiber
     (lambda ()
       (with-exception-handler
           (lambda (exn)
             (put-message reply (cons 'exception exn)))
         (lambda ()
           (call-with-values
               (lambda ()
                 (with-throw-handler #t
                   thunk
                   (lambda _
                     (backtrace))))
             (lambda vals
               (put-message reply vals))))
         #:unwind? #t))
     #:parallel? #t)
    reply))

(define (fetch-result-of-defered-thunks . reply-channels)
  (let ((responses (map get-message
                        reply-channels)))
    (map
     (match-lambda
       (('exception . exn)
        (raise-exception exn))
       (result
        (apply values result)))
     responses)))

(define-syntax parallel-via-fibers
  (lambda (x)
    (syntax-case x ()
      ((_ e0 ...)
       (with-syntax (((tmp0 ...) (generate-temporaries (syntax (e0 ...)))))
         #'(let ((tmp0 (defer-to-parallel-fiber
                         (lambda ()
                           e0)))
                 ...)
             (apply values (fetch-result-of-defered-thunks tmp0 ...))))))))

(define-syntax-rule (letpar& ((v e) ...) b0 b1 ...)
  (call-with-values
      (lambda () (parallel-via-fibers e ...))
    (lambda (v ...)
      b0 b1 ...)))

(define (par-mapper' mapper cons)
  (lambda (proc . lists)
    (apply
     fetch-result-of-defered-thunks
     (let loop ((lists lists))
       (match lists
         (((heads tails ...) ...)
          (let ((tail (loop tails))
                (head (defer-to-parallel-fiber
                        (lambda ()
                          (apply proc heads)))))
            (cons head tail)))
         (_
          '()))))))

(define par-map& (par-mapper' map cons))

(define (chunk lst max-length)
  (if (> (length lst)
         max-length)
      (call-with-values (lambda ()
                          (split-at lst max-length))
        (lambda (first-lst rest)
          (cons first-lst
                (chunk rest max-length))))
      (list lst)))

(define (chunk! lst max-length)
  (if (> (length lst)
         max-length)
      (call-with-values (lambda ()
                          (split-at! lst max-length))
        (lambda (first-lst rest)
          (cons first-lst
                (chunk! rest max-length))))
      (list lst)))

(define* (chunk-for-each! proc chunk-size #:rest lsts)
  (define (do-one-iteration lsts)
    (if (> (length (car lsts))
           chunk-size)
        (let ((chunks-and-rest
               (map (lambda (lst)
                      (call-with-values (lambda ()
                                          (split-at! lst chunk-size))
                        (lambda (first-lst rest)
                          (cons first-lst
                                rest))))
                    lsts)))
          (apply proc
                 (map car chunks-and-rest))
          (do-one-iteration
           (map cdr chunks-and-rest)))
        (apply proc lsts)))

  (let ((list-lengths (map length lsts)))
    (unless (eq? 1 (length (delete-duplicates list-lengths)))
      (error "lists not equal length"))

    (unless (eq? 0 (first list-lengths))
      (do-one-iteration lsts)))

  #t)

(define* (delete-duplicates/sort! unsorted-lst less #:optional (equal? equal?))
  (if (null? unsorted-lst)
      unsorted-lst
      (let ((sorted-lst (sort! unsorted-lst less)))

        (let loop ((lst (cdr sorted-lst))
                   (last-element (car sorted-lst))
                   (result (list (car sorted-lst))))
          (if (null? lst)
              result
              (let ((current-element (car lst)))
                (if (equal? current-element last-element)
                    (loop (cdr lst)
                          last-element
                          result)
                    (loop (cdr lst)
                          current-element
                          (cons current-element
                                result)))))))))

(define (get-guix-metrics-updater registry)
  (define guix-db "/var/guix/db/db.sqlite")
  (define guix-db-wal (string-append guix-db "-wal"))

  (let ((guix-db-bytes-metric
         (make-gauge-metric registry "guix_db_bytes"))
        (guix-db-wal-bytes-metric
         (make-gauge-metric registry "guix_db_wal_bytes")))
    (lambda ()
      (with-exception-handler
          (lambda _
            #f)
        (lambda ()
          (metric-set guix-db-bytes-metric (stat:size (stat guix-db)))
          (metric-set guix-db-wal-bytes-metric
                      (if (file-exists? guix-db-wal)
                          (stat:size (stat guix-db-wal))
                          0)))
        #:unwind? #t))))

;; This variant of run-server from the fibers library supports running
;; multiple servers within one process.
(define run-server/patched
  (let ((fibers-web-server-module
         (resolve-module '(fibers web server))))

    (define set-nonblocking!
      (module-ref fibers-web-server-module 'set-nonblocking!))

    (define make-default-socket
      (module-ref fibers-web-server-module 'make-default-socket))

    (define socket-loop
      (module-ref fibers-web-server-module 'socket-loop))

    (lambda* (handler
              #:key
              (host #f)
              (family AF_INET)
              (addr (if host
                        (inet-pton family host)
                        INADDR_LOOPBACK))
              (port 8080)
              (socket (make-default-socket family addr port)))
      ;; We use a large backlog by default.  If the server is suddenly hit
      ;; with a number of connections on a small backlog, clients won't
      ;; receive confirmation for their SYN, leading them to retry --
      ;; probably successfully, but with a large latency.
      (listen socket 1024)
      (set-nonblocking! socket)
      (sigaction SIGPIPE SIG_IGN)
      (spawn-fiber (lambda () (socket-loop socket handler))))))

(define &port-timeout
  (make-exception-type '&port-timeout
                       &external-error
                       '(port)))

(define make-port-timeout-error
  (record-constructor &port-timeout))

(define port-timeout-error?
  (record-predicate &port-timeout))

(define &port-read-timeout
  (make-exception-type '&port-read-timeout
                       &port-timeout
                       '()))

(define make-port-read-timeout-error
  (record-constructor &port-read-timeout))

(define port-read-timeout-error?
  (record-predicate &port-read-timeout))

(define &port-write-timeout
  (make-exception-type '&port-write-timeout
                       &port-timeout
                       '()))

(define make-port-write-timeout-error
  (record-constructor &port-write-timeout))

(define port-write-timeout-error?
  (record-predicate &port-write-timeout))

;; These procedure are subject to spurious wakeups.

(define (readable? port)
  "Test if PORT is writable."
  (match (select (vector port) #() #() 0)
    ((#() #() #()) #f)
    ((#(_) #() #()) #t)))

(define (writable? port)
  "Test if PORT is writable."
  (match (select #() (vector port) #() 0)
    ((#() #() #()) #f)
    ((#() #(_) #()) #t)))

(define (make-wait-operation ready? schedule-when-ready port
                             port-ready-fd this-procedure)
  (make-base-operation
   #f
   (lambda _
     (and (ready? (port-ready-fd port)) values))
   (lambda (flag sched resume)
     (define (commit)
       (match (atomic-box-compare-and-swap! flag 'W 'S)
         ('W (resume values))
         ('C (commit))
         ('S #f)))
     (schedule-when-ready
      sched (port-ready-fd port) commit))))

(define (wait-until-port-readable-operation port)
  "Make an operation that will succeed when PORT is readable."
  (unless (input-port? port)
    (error "refusing to wait forever for input on non-input port"))
  (make-wait-operation readable? schedule-task-when-fd-readable port
                       port-read-wait-fd
                       wait-until-port-readable-operation))

(define (wait-until-port-writable-operation port)
  "Make an operation that will succeed when PORT is writable."
  (unless (output-port? port)
    (error "refusing to wait forever for output on non-output port"))
  (make-wait-operation writable? schedule-task-when-fd-writable port
                       port-write-wait-fd
                       wait-until-port-writable-operation))

(define* (with-fibers-port-timeouts thunk
                                    #:key timeout
                                    (read-timeout timeout)
                                    (write-timeout timeout))
  (define (no-fibers-wait port mode timeout)
    (define poll-timeout-ms 200)

    ;; When the GC runs, it restarts the poll syscall, but the timeout
    ;; remains unchanged! When the timeout is longer than the time
    ;; between the syscall restarting, I think this renders the
    ;; timeout useless. Therefore, this code uses a short timeout, and
    ;; repeatedly calls poll while watching the clock to see if it has
    ;; timed out overall.
    (let ((timeout-internal
           (+ (get-internal-real-time)
              (* internal-time-units-per-second
                 (/ timeout 1000)))))
      (let loop ((poll-value
                  (port-poll port mode poll-timeout-ms)))
        (if (= poll-value 0)
            (if (> (get-internal-real-time)
                   timeout-internal)
                (raise-exception
                 (if (string=? mode "r")
                     (make-port-read-timeout-error port)
                     (make-port-write-timeout-error port)))
                (loop (port-poll port mode poll-timeout-ms)))
            poll-value))))

  (parameterize
      ((current-read-waiter
        (lambda (port)
          (if (current-scheduler)
              (perform-operation
               (choice-operation
                (wait-until-port-readable-operation port)
                (wrap-operation
                 (sleep-operation read-timeout)
                 (lambda ()
                   (raise-exception
                    (make-port-read-timeout-error thunk port))))))
              (no-fibers-wait port "r" read-timeout))))
       (current-write-waiter
        (lambda (port)
          (if (current-scheduler)
              (perform-operation
               (choice-operation
                (wait-until-port-writable-operation port)
                (wrap-operation
                 (sleep-operation write-timeout)
                 (lambda ()
                   (raise-exception
                    (make-port-write-timeout-error thunk port))))))
              (no-fibers-wait port "w" write-timeout)))))
    (thunk)))

(define (spawn-port-monitoring-fiber port error-condition)
  (spawn-fiber
   (lambda ()
     (while #t
       (sleep 20)
       (with-exception-handler
           (lambda (exn)
             (simple-format (current-error-port)
                            "port monitoring fiber failed to connect to ~A: ~A\n"
                            port exn)
             (signal-condition! error-condition))
         (lambda ()
           (with-fibers-port-timeouts
            (lambda ()
              (let ((sock (socket PF_INET SOCK_STREAM 0)))
                (connect sock AF_INET INADDR_LOOPBACK port)
                (close-port sock)))
            #:timeout 20))
         #:unwind? #t)))))

;; Copied from (fibers web server)
(define (call-with-sigint thunk cvar)
  (let ((handler #f))
    (dynamic-wind
      (lambda ()
        (set! handler
          (sigaction SIGINT (lambda (sig) (signal-condition! cvar)))))
      thunk
      (lambda ()
        (if handler
            ;; restore Scheme handler, SIG_IGN or SIG_DFL.
            (sigaction SIGINT (car handler) (cdr handler))
            ;; restore original C handler.
            (sigaction SIGINT #f))))))