path: root/guix-build-coordinator/utils.scm

(define-module (guix-build-coordinator utils)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-19)
  #:use-module (srfi srfi-26)
  #:use-module (srfi srfi-60)
  #:use-module (ice-9 q)
  #:use-module (ice-9 ftw)
  #:use-module (ice-9 popen)
  #:use-module (ice-9 iconv)
  #:use-module (ice-9 match)
  #:use-module (ice-9 format)
  #:use-module (ice-9 threads)
  #:use-module (ice-9 textual-ports)
  #:use-module (ice-9 rdelim)
  #:use-module (ice-9 binary-ports)
  #:use-module (ice-9 exceptions)
  #:use-module (rnrs bytevectors)
  #:use-module (web uri)
  #:use-module (web http)
  #:use-module (web client)
  #:use-module (web request)
  #:use-module (web response)
  #:use-module (gcrypt pk-crypto)
  #:use-module (gcrypt hash)
  #:use-module (gcrypt random)
  #:use-module (json)
  #:use-module (prometheus)
  #:use-module (guix pki)
  #:use-module (guix utils)
  #:use-module (guix config)
  #:use-module (guix store)
  #:use-module (guix status)
  #:use-module (guix base64)
  #:use-module (guix scripts substitute)
  #:export (random-v4-uuid

            make-base64-output-port

            with-gc-protection

            request-query-parameters

            call-with-streaming-http-request
            make-chunked-input-port*

            find-missing-substitutes-for-output
            has-substiutes-no-cache?

            substitute-derivation

            narinfo-string

            retry-on-error

            s3-list-objects
            s3-cp

            with-time-logging

            create-work-queue

            with-timeout

            get-load-average

            running-on-the-hurd?

            get-gc-metrics-updater))

(eval-when (eval load compile)
  (begin
    (when (defined? 'narinfo-references (resolve-module '(guix narinfo)))
      ;; This module contains narinfo-references in newer version of Guix
      (use-modules (guix narinfo)))

    (when (defined? 'lookup-narinfos (resolve-module '(guix substitutes)))
      ;; This module may contain lookup-narinfos in newer version of Guix
      (use-modules (guix substitutes)))))

(define (random-v4-uuid)
  ;; https://tools.ietf.org/html/rfc4122#page-14
  ;;
  ;; The pattern in characters is: 8, 4, 4, 4, 12
  ;; The pattern in bytes is:      4, 2, 2, 2, 6
  ;;
  ;; time-low "-" time-mid "-" time-high-and-version "-"
  ;;   clock-seq-and-reserved clock-seq-low "-" node
  ;;
  ;; - Set the two most significant bits (bits 6 and 7) of the
  ;;   clock_seq_hi_and_reserved to zero and one, respectively.
  ;; - Set the four most significant bits (bits 12 through 15) of the
  ;;   time_hi_and_version field to the 4-bit version number from
  ;;   Section 4.1.3.

  (let* ((bytes 16)
         (bv (gen-random-bv bytes)))

    (let ((version 4)
          (6th-byte (array-ref bv 6))   ; Most significant byte in
                                        ; time_hi_and_version
          (8th-byte (array-ref bv 8)))  ; Most significant byte in
                                        ; clock_seq_hi_and_reserved

      (array-set!
       bv
       (logior (logand #b00001111 6th-byte)
               (rotate-bit-field version 4 0 8))
       6)

      (array-set!
       bv
       ;; Set bits 6 and 7 to 0 and 1 respectively
       (logior #b10000000
               (logand #b00111111
                       8th-byte))
       8))

    (let* ((int
            (bytevector-uint-ref bv 0 (endianness big) bytes))
           (hex-string
            (format #f "~32,'0x" int)))
      (string-join
       (fold (lambda (part-length result)
               (let ((start (string-length
                             (string-join result ""))))
                 (append
                  result
                  (list (substring hex-string
                                   start
                                   (+ start part-length))))))
             '()
             (list 8 4 4 4 12))
       "-"))))


(define (make-base64-output-port port)
  (define line-length 72)               ; must be a multiple of 4
  (define buffer-length
    (let ((bytes-per-line (* 3 (/ 72 4)))
          (lines-per-buffer 65536))
      (* bytes-per-line lines-per-buffer)))

  (define buffer (make-bytevector buffer-length))
  (define buffered-bytes 0)

  (define (write! bv start count)
    (let ((remaining-buffer-space (- buffer-length buffered-bytes)))
      (if (<= count remaining-buffer-space)
          (begin
            (bytevector-copy! bv start
                              buffer buffered-bytes count)
            (set! buffered-bytes (+ buffered-bytes count))
            count)
          (begin
            (bytevector-copy! bv start
                              buffer buffered-bytes remaining-buffer-space)
            (base64-encode buffer 0 buffer-length line-length
                           #f base64-alphabet port)
            (set! buffered-bytes 0)
            remaining-buffer-space))))

  (define (close)
    (base64-encode buffer 0 buffered-bytes line-length
                   #f base64-alphabet port)
    (set! buffer #f)
    (set! buffered-bytes 0)
    #t)

  (make-custom-binary-output-port
   "base64-output"
   write!
   #f
   #f
   close))

;; Chunked Responses
(define (read-chunk-header port)
  "Read a chunk header from PORT and return the size in bytes of the
upcoming chunk."
  (match (read-line port)
    ((? eof-object?)
     ;; Connection closed prematurely: there's nothing left to read.
     0)
    (str
     (let ((extension-start (string-index str
                                          (lambda (c)
                                            (or (char=? c #\;)
                                                (char=? c #\return))))))
       (string->number (if extension-start       ; unnecessary?
                           (substring str 0 extension-start)
                           str)
                       16)))))

(define* (make-chunked-input-port* port #:key (keep-alive? #f))
  (define (close)
    (unless keep-alive?
      (close-port port)))

  (define chunk-size 0)     ;size of the current chunk
  (define remaining 0)      ;number of bytes left from the current chunk
  (define finished? #f)     ;did we get all the chunks?

  (define (read! bv idx to-read)
    (define (loop to-read num-read)
      (cond ((or finished? (zero? to-read))
             num-read)
            ((zero? remaining)                    ;get a new chunk
             (let ((size (read-chunk-header port)))
               (set! chunk-size size)
               (set! remaining size)
               (cond
                ((zero? size)
                 (set! finished? #t)
                 (get-bytevector-n port 2) ; \r\n follows the last chunk
                 num-read)
                (else
                 (loop to-read num-read)))))
            (else                           ;read from the current chunk
             (let* ((ask-for (min to-read remaining))
                    (read    (get-bytevector-n! port bv (+ idx num-read)
                                                ask-for)))
               (cond
                ((eof-object? read)     ;premature termination
                 (error "chunked input ended prematurely"))
                (else
                 (let ((left (- remaining read)))
                   (set! remaining left)
                   (when (zero? left)
                     ;; We're done with this chunk; read CR and LF.
                     (get-u8 port) (get-u8 port))
                   (loop (- to-read read)
                         (+ num-read read)))))))))
    (loop to-read 0))

  (make-custom-binary-input-port "chunked input port" read! #f #f close))

(define (request-query-parameters request)
  (define (parse-query-string query)
    "Parse and decode the URI query string QUERY and return an alist."
    (let lp ((lst (map uri-decode (string-split query (char-set #\& #\=)))))
      (match lst
        ((key value . rest)
         (cons (cons key value) (lp rest)))
        (("") '())
        (() '()))))

  (let ((query (uri-query (request-uri request))))
    (if (and query
             (not (string-null? query)))
        (map (match-lambda
               ((name . value)
                (cons (string->symbol name)
                      value)))
             (parse-query-string query))
        '())))

(define (with-gc-protection thunk)
  (dynamic-wind
    gc-disable
    thunk
    gc-enable))

(define* (make-chunked-output-port* port #:key (keep-alive? #f)
                                    (buffering 1200))
  (define initial-heap-size
    (assq-ref (gc-stats) 'heap-size))

  (define (%put-string s)
    (unless (string-null? s)
      (let* ((bv (string->bytevector s "ISO-8859-1"))
             (length (bytevector-length bv)))
        (with-gc-protection
         (lambda ()
           (put-string port (number->string length 16))
           (put-string port "\r\n")
           (put-bytevector port bv)
           (put-string port "\r\n")))

        (let* ((stats (gc-stats))
               (initial-gc-times
                (assq-ref stats 'gc-times)))
          (while (let ((updated-stats (gc-stats)))
                   (and (> (assq-ref updated-stats 'heap-allocated-since-gc)
                           initial-heap-size)
                        (= initial-gc-times
                           (assq-ref updated-stats 'gc-times))))
            (gc)
            (usleep 10))))))

  (define (%put-char c)
    (%put-string (list->string (list c))))

  (define (flush) #t)
  (define (close)
    (with-gc-protection
     (lambda ()
       (put-string port "0\r\n\r\n")
       (force-output port)
       (unless keep-alive?
         (close-port port)))))
  (let ((ret (make-soft-port
              (vector %put-char %put-string flush #f close) "w")))
    (setvbuf ret 'block buffering)
    ret))

(define* (call-with-streaming-http-request uri callback
                                           #:key (headers '()))
  (let* ((port (open-socket-for-uri uri))
         (request
          (build-request
           uri
           #:method 'PUT
           #:version '(1 . 1)
           #:headers `((connection close)
                       (Transfer-Encoding . "chunked")
                       (Content-Type . "application/octet-stream")
                       ,@headers)
           #:port port)))

    (set-port-encoding! port "ISO-8859-1")
    (setvbuf port 'block (expt 2 13))
    (with-exception-handler
        (lambda (exp)
          (simple-format #t "error: PUT ~A: ~A\n" (uri-path uri) exp)
          (close-port port)
          (raise-exception exp))
      (lambda ()
        (let ((request (write-request request port)))
          (let* ((chunked-output-port
                  (make-chunked-output-port*
                   port
                   #:buffering (expt 2 12)
                   #:keep-alive? #t)))

            ;; A SIGPIPE will kill Guile, so ignore it
            (sigaction SIGPIPE
              (lambda (arg)
                (simple-format (current-error-port) "warning: SIGPIPE\n")))

            (set-port-encoding! chunked-output-port "ISO-8859-1")
            (callback chunked-output-port)
            (close-port chunked-output-port)

            (with-gc-protection
             (lambda ()
               (let ((response (read-response port)))
                 (let ((body (read-response-body response)))
                   (close-port port)
                   (values response
                           body)))))))))))

(define (find-missing-substitutes-for-output store substitute-urls output)
  (if (valid-path? store output)
      '()
      (let ((narinfo
             (any (lambda (substitute-url)
                    (let ((result (lookup-narinfos substitute-url (list output))))
                      (if (null? result)
                          #f
                          (first result))))
                  substitute-urls)))
        (if narinfo
            (append-map
             (lambda (reference)
               (let ((referenced-output
                      (string-append (%store-prefix) "/" reference)))
                 (if (string=? referenced-output output)
                     '()
                     (find-missing-substitutes-for-output store
                                                          substitute-urls
                                                          referenced-output))))
             (narinfo-references narinfo))
            (list output)))))

;; Work around Guix holding on to broken connections to substitute servers
;; (because of mishandling gnutls errors).
(let ((mod (resolve-module '(guix scripts substitute))))
  (when (module-variable mod '%max-cached-connections)
    (module-set! mod '%max-cached-connections 0)))

(define (has-substiutes-no-cache? substitute-urls file)
  (define %narinfo-cache-directory
    (if (zero? (getuid))
        (or (and=> (getenv "XDG_CACHE_HOME")
                   (cut string-append <> "/guix/substitute"))
            (string-append %state-directory "/substitute/cache"))
        (string-append (cache-directory #:ensure? #f) "/substitute")))

  ;; Because there's no control over the caching of 404 lookups, and I'd
  ;; rather not reach inside and monkey patch the Guix code, just delete any
  ;; cache files
  (let ((hash-part (store-path-hash-part file))
        (directories
         (scandir %narinfo-cache-directory
                  (lambda (s) (= (string-length s) 52)))))

    (for-each (lambda (directory)
                (let ((cache-file
                       (string-append
                        %narinfo-cache-directory "/"
                        directory "/" hash-part)))
                  ;; Use monitor to avoid multiple threads trying to delete
                  ;; the same file at the same time
                  (monitor
                   (when (file-exists? cache-file)
                     (with-exception-handler
                         (lambda (exn)
                           (simple-format
                            (current-error-port)
                            "error: when deleting substitute cache file: ~A\n"
                            exn))
                       (lambda ()
                         (delete-file cache-file))
                       #:unwind? #t)))))
              (or directories '())))

  (let ((substitute-urls
         (append-map (lambda (substitute-url)
                       (let ((log-port (open-output-string)))
                         (with-throw-handler #t
                           (lambda ()
                             (if (null?
                                  ;; I doubt the caching is thread safe, so
                                  ;; only make one request at a time.
                                  (monitor
                                   (parameterize ((current-error-port log-port))
                                     (lookup-narinfos substitute-url
                                                      (list file)))))
                                 '()
                                 (list substitute-url)))
                           (lambda (key . args)
                             (simple-format
                              (current-error-port)
                              "exception in has-substiutes-no-cache? (~A) ~A: ~A\n"
                              substitute-url key args)
                             (display (string-append
                                       (get-output-string log-port)
                                       "\n")
                                      (current-error-port))
                             (close-output-port log-port)))))
                     substitute-urls)))
    substitute-urls))

(define* (substitute-derivation derivation-name
                                #:key substitute-urls)
  (let ((log-port (open-output-string)))
    (catch #t
      (lambda ()
        (if (defined? 'ensure-path
              (resolve-module '(guix store)))
            (with-store store
              (apply set-build-options
                     store
                     `(,@(if substitute-urls
                             `(#:substitute-urls ,substitute-urls)
                             '())
                       #:max-silent-time 60
                       #:timeout ,(* 10 60)))

              (parameterize ((current-build-output-port log-port))
                (ensure-path store derivation-name)))
            (with-store store
              (apply set-build-options
                     store
                     `(#:print-extended-build-trace? #t
                       #:multiplexed-build-output? #t
                       ,@(if substitute-urls
                             `(#:substitute-urls ,substitute-urls)
                             '())))

              (with-status-report
                  (lambda (event status new)
                    (print-build-event event status new)
                    (match event
                      (('substituter-succeeded substituted-drv)
                       (when (string=? derivation-name
                                       substituted-drv)
                         (close-connection store)))
                      (_ #t)))
                (build-things store (list derivation-name))))))
      (lambda (key . args)
        (let ((log-string
               (get-output-string log-port)))
          (close-output-port log-port)
          ;; This is a hack, to ignore errors relating to closing the store
          ;; connection.
          (if (with-store store
                (valid-path? store derivation-name))
              #t
              (begin
                (display log-string)
                (error (simple-format #f "could not substitute ~A\n"
                                      derivation-name)))))))))

(define* (narinfo-string store-path hash size references
                         compressed-files
                         #:key (nar-path "nar")
                         system derivation
                         public-key private-key)
  (define (signed-string s)
    (let* ((hash (bytevector->hash-data (sha256 (string->utf8 s))
                                        #:key-type (key-type public-key))))
      (signature-sexp hash private-key public-key)))

  (define base64-encode-string
    (compose base64-encode string->utf8))

  (define* (store-item->recutils compression file-size)
    (let ((url (encode-and-join-uri-path
                `(,@(split-and-decode-uri-path nar-path)
                  ,@(if compression
                        (list (symbol->string compression))
                        '())
                  ,(basename store-path)))))
      (format #f "URL: ~a~%Compression: ~a~%~@[FileSize: ~a~%~]"
              url
              (or compression "none")
              file-size)))

  (let* ((base-info  (format #f
                             "\
StorePath: ~a
~{~a~}\
NarHash: sha256:~a
NarSize: ~d
References: ~a~%"
                             store-path
                             (map (match-lambda
                                    ((compression compressed-size)
                                     (store-item->recutils compression
                                                           compressed-size)))
                                  compressed-files)
                             hash size
                             (string-join references " ")))
         ;; Do not render a "Deriver" or "System" line if we are rendering
         ;; info for a derivation.
         (info       (if derivation
                         (format #f "~aSystem: ~a~%Deriver: ~a~%"
                                 base-info
                                 system
                                 (basename derivation))
                         base-info))
         (signature  (base64-encode-string
                      (canonical-sexp->string (signed-string info)))))
  (format #f "~aSignature: 1;~a;~a~%" info (gethostname) signature)))

(define* (retry-on-error f #:key times delay ignore)
  (let loop ((attempt 1))
    (match (with-exception-handler
               (lambda (exn)
                 (when (cond
                        ((list? ignore)
                         (any (lambda (test)
                                (test exn))
                              ignore))
                        ((procedure? ignore)
                         (ignore exn))
                        (else #f))
                   (raise-exception exn))

                 (cons #f exn))
             (lambda ()
               (cons #t (f)))
             #:unwind? #t)
      ((#t . return-value)
       (when (> attempt 1)
         (simple-format
          (current-error-port)
          "retry success: ~A\n  on attempt ~A of ~A\n"
          f
          attempt
          times))
       return-value)
      ((#f . exn)
       (if (>= attempt times)
           (begin
             (simple-format
              (current-error-port)
              "error: ~A:\n  ~A,\n  giving up after ~A attempts\n"
              f
              exn
              times)
             (raise-exception exn))
           (begin
             (simple-format
              (current-error-port)
              "error: ~A:\n  ~A,\n  attempt ~A of ~A, retrying in ~A\n"
              f
              exn
              attempt
              times
              delay)
             (sleep delay)
             (loop (+ 1 attempt))))))))

(define* (s3-list-objects s3-bucket prefix
                          #:key
                          (command "aws")
                          (command-line-arguments '()))
  (let ((command
         `(,command
           "s3api"
           ,@command-line-arguments
           "list-objects"
           "--bucket" ,s3-bucket
           "--prefix" ,prefix)))
    (simple-format
     #t
     "running: ~A\n"
     (string-join command))
    (let ((pipe (apply open-pipe*
                       OPEN_READ
                       command)))

      (let ((output    (get-string-all pipe))
            (exit-code (status:exit-val
                        (close-pipe pipe))))
        (if (zero? exit-code)
            (if (string-null? output)
                '()
                (json-string->scm output))
            (raise-exception
             (make-exception-with-message
              output)))))))

(define* (s3-cp s3-bucket source destination
                #:key
                (command "aws")
                (command-line-arguments '()))
  (let ((command
         `(,command
           "s3"
           ,@command-line-arguments
           "cp"
           ,source
           ,(simple-format #f "s3://~A/~A"
                           s3-bucket destination))))
    (simple-format
     #t
     "running: ~A\n"
     (string-join command))
    (let ((exit-code
           (status:exit-val
            (apply system* command))))
      (unless (zero? exit-code)
        (raise-exception
         (make-exception-with-message
          (simple-format
           #f
           "error: command failed (~A): ~A\n"
           exit-code
           command))))
      #t)))

(define (call-with-time-logging name thunk)
  (let ((start   (current-time time-utc)))
    (call-with-values
        thunk
      (lambda vals
        (let* ((end     (current-time time-utc))
               (elapsed (time-difference end start)))
          (display
           (format #f
                   "~a took ~f seconds~%"
                   name
                   (+ (time-second elapsed)
                      (/ (time-nanosecond elapsed) 1e9))))
          (apply values vals))))))

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

(define* (create-work-queue thread-count-parameter proc
                            #:key thread-start-delay)
  (let ((queue (make-q))
        (queue-mutex (make-mutex))
        (job-available (make-condition-variable))
        (running-job-args (make-hash-table)))

    (define get-thread-count
      (if (number? thread-count-parameter)
          (const thread-count-parameter)
          thread-count-parameter))

    (define (process-job . args)
      (with-mutex queue-mutex
        (enq! queue args)
        (start-new-threads-if-necessary (get-thread-count))
        (signal-condition-variable job-available)))

    (define (count-threads)
      (with-mutex queue-mutex
        (hash-count (const #t) running-job-args)))

    (define (count-jobs)
      (with-mutex queue-mutex
        (+ (q-length queue)
           (hash-count (lambda (index val)
                         (list? val))
                       running-job-args))))

    (define (list-jobs)
      (with-mutex queue-mutex
        (append (list-copy
                 (car queue))
                (hash-fold (lambda (key val result)
                             (or (and val
                                      (cons val result))
                                 result))
                           '()
                           running-job-args))))

    (define (thread-process-job thread-index)
      (and=>
       (with-exception-handler
           (lambda (exn)
             (simple-format (current-error-port)
                            "thread ~A: exception for deq!: ~A\n"
                            thread-index exn)
             (unlock-mutex queue-mutex)
             #f)
         (lambda ()
           (deq! queue))
         #:unwind? #t)
       (lambda (job-args)
         (hash-set! running-job-args
                    thread-index
                    job-args)
         (unlock-mutex queue-mutex)
         (with-exception-handler
             (lambda (exn)
               (simple-format (current-error-port)
                              "job raised exception: ~A\n"
                              job-args))
           (lambda ()
             (with-throw-handler #t
               (lambda ()
                 (apply proc job-args))
               (lambda (key . args)
                 (simple-format (current-error-port)
                                "exception when handling job: ~A ~A\n"
                                key args)
                 (backtrace))))
           #:unwind? #t)
         (with-mutex queue-mutex
           (hash-set! running-job-args
                      thread-index
                      #f)))))

    (define (start-thread thread-index)
      (define (too-many-threads?)
        (let ((running-jobs-count
               (hash-count (lambda (index val)
                             (list? val))
                           running-job-args))
              (idle-thread-count
               (hash-count (lambda (index val)
                             (eq? #f val))
                           running-job-args))
              (desired-thread-count (get-thread-count)))
          (or (>= running-jobs-count desired-thread-count)
              (> idle-thread-count 2))))

      (define (stop-thread)
        (hash-remove! running-job-args
                      thread-index)
        (unlock-mutex queue-mutex))

      (call-with-new-thread
       (lambda ()
         (let loop ()
           (lock-mutex queue-mutex)

           (if (too-many-threads?)
               (stop-thread)
               (if (q-empty? queue)
                   ;; #f from wait-condition-variable indicates a timeout
                   (if (wait-condition-variable
                        job-available
                        queue-mutex
                        (+ 9 (time-second (current-time))))
                       ;; Another thread could have taken the job in the
                       ;; mean time
                       (if (q-empty? queue)
                           (unlock-mutex queue-mutex)
                           ;; thread-process-job will unlock queue-mutex
                           (thread-process-job thread-index))
                       (unlock-mutex queue-mutex))
                   (thread-process-job thread-index)))
           (loop)))))

    (define start-new-threads-if-necessary
      (let ((previous-thread-started-at (make-time time-monotonic 0 0)))
        (lambda (desired-count)
            (let* ((thread-count
                    (hash-count (const #t) running-job-args))
                   (threads-to-start
                    (- desired-count thread-count)))
              (when (> threads-to-start 0)
                (for-each
                 (lambda (thread-index)
                   (when (eq? (hash-ref running-job-args
                                        thread-index
                                        'slot-free)
                              'slot-free)
                     (let* ((now     (current-time time-monotonic))
                            (elapsed (time-difference now
                                                      previous-thread-started-at)))
                       (when (or (eq? #f thread-start-delay)
                                 (time>=? elapsed thread-start-delay))
                         (set! previous-thread-started-at now)
                         (hash-set! running-job-args
                                    thread-index
                                    #f)
                         (start-thread thread-index)))))
                 (iota desired-count)))))))

    (if (procedure? thread-count-parameter)
        (call-with-new-thread
         (lambda ()
           (while #t
             (sleep 15)
             (with-mutex queue-mutex
               (let ((idle-threads (hash-count (lambda (index val)
                                                 (eq? #f val))
                                               running-job-args)))
                 (when (= 0 idle-threads)
                   (start-new-threads-if-necessary (get-thread-count))))))))
        (start-new-threads-if-necessary (get-thread-count)))

    (values process-job count-jobs count-threads list-jobs)))

(define %random-state
  (seed->random-state (+ (ash (cdr (gettimeofday)) 32) (getpid))))

;; copied from (guix scripts substitute)
(define-syntax-rule (with-timeout duration handler body ...)
  "Run BODY; when DURATION seconds have expired, call HANDLER, and run BODY
again."
  (begin
    (sigaction SIGALRM
      (lambda (signum)
        (sigaction SIGALRM SIG_DFL)
        handler))
    (alarm duration)
    (call-with-values
        (lambda ()
          (let try ()
            (catch 'system-error
              (lambda ()
                body ...)
              (lambda args
                ;; Before Guile v2.0.9-39-gfe51c7b, the SIGALRM triggers EINTR
                ;; because of the bug at
                ;; <http://lists.gnu.org/archive/html/guile-devel/2013-06/msg00050.html>.
                ;; When that happens, try again.  Note: SA_RESTART cannot be
                ;; used because of <http://bugs.gnu.org/14640>.
                (if (= EINTR (system-error-errno args))
                    (begin
                      ;; Wait a little to avoid bursts.
                      (usleep (random 3000000 %random-state))
                      (try))
                    (apply throw args))))))
      (lambda result
        (alarm 0)
        (sigaction SIGALRM SIG_DFL)
        (apply values result)))))

(define* (get-load-average #:key (period 5))
  (if (file-exists? "/proc/loadavg")
      (let ((line (call-with-input-file "/proc/loadavg" get-line)))
        (match (string-split line #\space)
          ((1min 5min 15min _ _)
           (string->number
            (cond
             ((= period 1) 1min)
             ((= period 5) 5min)
             ((= period 15) 15min))))))
      #f))

(define (running-on-the-hurd?)
  (let ((cached-system #f))
    (unless cached-system
      (set! cached-system (utsname:sysname (uname))))
    (string=? cached-system "GNU")))

(define (get-gc-metrics-updater registry)
  (define metrics
    `((gc-time-taken
       . ,(make-gauge-metric registry "guile_gc_time_taken"))
      (heap-size
       . ,(make-gauge-metric registry "guile_heap_size"))
      (heap-free-size
       . ,(make-gauge-metric registry "guile_heap_free_size"))
      (heap-total-allocated
       . ,(make-gauge-metric registry "guile_heap_total_allocated"))
      (heap-allocated-since-gc
       . ,(make-gauge-metric registry "guile_allocated_since_gc"))
      (protected-objects
       . ,(make-gauge-metric registry "guile_gc_protected_objects"))
      (gc-times
       . ,(make-gauge-metric registry "guile_gc_times"))))

  (lambda ()
    (let ((stats (gc-stats)))
      (for-each
       (match-lambda
         ((name . metric)
          (let ((value (assq-ref stats name)))
            (metric-set metric value))))
       metrics))))