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

(define-module (guix-build-coordinator utils fibers)
  #:use-module (ice-9 match)
  #:use-module (ice-9 threads)
  #:use-module (fibers)
  #:use-module (fibers timers)
  #:use-module (fibers channels)
  #:use-module (fibers operations)
  #:use-module (fibers conditions)
  #:use-module ((guix build syscalls)
                #:select (set-thread-name))
  #:use-module (guix-build-coordinator utils)
  #:export (make-worker-thread-channel
            call-with-worker-thread
            worker-thread-timeout-error?

            call-with-sigint

            run-server/patched

            letpar&

            with-fibers-timeout))

(define %worker-thread-args
  (make-parameter #f))

(define* (make-worker-thread-channel initializer
                                     #:key (parallelism 1)
                                     (delay-logger (lambda _ #f))
                                     (duration-logger (const #f))
                                     destructor
                                     lifetime
                                     (log-exception? (const #t))
                                     (expire-on-exception? #f)
                                     (name "unnamed"))
  "Return a channel used to offload work to a dedicated thread.  ARGS are the
arguments of the worker thread procedure."

  (define (initializer/safe)
    (let ((args
           (with-exception-handler
               (lambda (exn)
                 (simple-format
                  (current-error-port)
                  "exception running initializer in worker thread (~A): ~A:\n  ~A\n"
                  name
                  initializer
                  exn)
                 #f)
             (lambda ()
               (with-throw-handler #t
                 initializer
                 (lambda args
                   (backtrace))))
             #:unwind? #t)))

      (if args
          args
          ;; never give up, just keep retrying
          (begin
            (sleep 5)
            (initializer/safe)))))

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

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

  (define (process channel args)
    (let loop ((current-lifetime lifetime))
      (let ((exception?
             (match (get-message channel)
               (((? channel? reply) sent-time (? procedure? proc))
                (let ((time-delay
                       (- (get-internal-real-time)
                          sent-time)))
                  (delay-logger (/ time-delay
                                   internal-time-units-per-second))

                  (let* ((start-time (get-internal-real-time))
                         (response
                          (with-exception-handler
                              (lambda (exn)
                                (list 'worker-thread-error
                                      (/ (- (get-internal-real-time)
                                            start-time)
                                         internal-time-units-per-second)
                                      exn))
                            (lambda ()
                              (with-throw-handler #t
                                (lambda ()
                                  (call-with-values
                                      (lambda ()
                                        (start-stack
                                         'worker-thread
                                         (apply proc args)))
                                    (lambda vals
                                      (cons (/ (- (get-internal-real-time)
                                                  start-time)
                                               internal-time-units-per-second)
                                            vals))))
                                (lambda args
                                  (when (match args
                                          (('%exception exn)
                                           (log-exception? exn))
                                          (_ #t))
                                    (simple-format
                                     (current-error-port)
                                     "worker-thread: exception: ~A\n" args)
                                    (backtrace)))))
                            #:unwind? #t)))
                    (put-message reply
                                 response)

                    (match response
                      (('worker-thread-error duration _)
                       (when duration-logger
                         (duration-logger duration proc))
                       #t)
                      ((duration . _)
                       (when duration-logger
                         (duration-logger duration proc))
                       #f))))))))
        (unless (and expire-on-exception?
                     exception?)
          (if (number? current-lifetime)
              (unless (< current-lifetime 0)
                (loop (if current-lifetime
                          (- current-lifetime 1)
                          #f)))
              (loop #f))))))

  (let ((channel (make-channel)))
    (for-each
     (lambda (thread-index)
       (call-with-new-thread
        (lambda ()
          (catch 'system-error
            (lambda ()
              (set-thread-name
               (string-append
                name " w t "
                (number->string thread-index))))
            (const #t))

          (let init ((args (initializer/safe)))
            (with-exception-handler
                (lambda (exn)
                  (simple-format
                   (current-error-port)
                   "worker-thread-channel: exception: ~A\n" exn))
              (lambda ()
                (parameterize ((%worker-thread-args args))
                  (process channel args)))
              #:unwind? #t)

            (when destructor
              (destructor/safe args))

            (init (initializer/safe))))))
     (iota parallelism))
    channel))

(define &worker-thread-timeout
  (make-exception-type '&worker-thread-timeout
                       &error
                       '()))

(define make-worker-thread-timeout-error
  (record-constructor &worker-thread-timeout))

(define worker-thread-timeout-error?
  (record-predicate &worker-thread-timeout))

(define* (call-with-worker-thread channel proc #:key duration-logger
                                  (timeout 30))
  "Send PROC to the worker thread through CHANNEL.  Return the result of PROC.
If already in the worker thread, call PROC immediately."
  (let ((args (%worker-thread-args)))
    (if args
        (call-with-delay-logging proc #:args args)
        (let* ((reply (make-channel))
               (operation-success?
                (perform-operation
                 (let ((put
                        (wrap-operation
                         (put-operation channel
                                        (list reply
                                              (get-internal-real-time)
                                              proc))
                         (const #t))))

                   (if timeout
                       (choice-operation
                        put
                        (wrap-operation (sleep-operation timeout)
                                        (const #f)))
                       put)))))

          (unless operation-success?
            (raise-exception
             (make-worker-thread-timeout-error)))

          (match (get-message reply)
            (('worker-thread-error duration exn)
             (when duration-logger
               (duration-logger duration))
             (raise-exception exn))
            ((duration . result)
             (when duration-logger
               (duration-logger duration))
             (apply values result)))))))

;; 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))))))

;; 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 (defer-to-fiber thunk)
  (let ((reply (make-channel)))
    (spawn-fiber
     (lambda ()
       (put-message
        reply
        (with-exception-handler
            (lambda (exn)
              (cons 'worker-fiber-error exn))
          (lambda ()
            (with-exception-handler
                (lambda (exn)
                  (simple-format
                   (current-error-port)
                   "worker fiber: exception: ~A\n"
                   exn)
                  (backtrace)
                  (raise-exception exn))
              (lambda ()
                (call-with-values
                    thunk
                  (lambda vals
                    vals)))))
          #:unwind? #t)))
     #:parallel? #t)
    reply))

(define (fetch-result-of-defered-thunks . reply-channels)
  (let ((responses (map get-message reply-channels)))
    (map
     (match-lambda
       (('worker-thread-error . 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-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* (with-fibers-timeout thunk #:key timeout on-timeout)
  (let ((channel (make-channel)))
    (spawn-fiber
     (lambda ()
       (with-exception-handler
           (lambda (exn)
             (perform-operation
              (choice-operation
               (put-operation channel (cons 'exception exn))
               (sleep-operation timeout))))
         (lambda ()
           (call-with-values thunk
             (lambda vals
               (perform-operation
                (choice-operation
                 (put-operation channel vals)
                 (sleep-operation timeout))))))
         #:unwind? #t)))

    (match (perform-operation
            (choice-operation
             (get-operation channel)
             (wrap-operation (sleep-operation timeout)
                             (const 'timeout))))
      ('timeout
       (on-timeout))
      (('exception . exn)
       (raise-exception exn))
      (vals
       (apply values vals)))))