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;;;; base.scm -- core procedures
;;; Copyright © 2003 Dale Mellor <dale_mellor@users.sourceforge.net>
;;; Copyright © 2015, 2016 Mathieu Lirzin <mthl@gnu.org>
;;; Copyright © 2016 Ludovic Courtès <ludo@gnu.org>
;;;
;;; This file is part of GNU Mcron.
;;;
;;; GNU Mcron is free software: you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License as published by
;;; the Free Software Foundation, either version 3 of the License, or
;;; (at your option) any later version.
;;;
;;; GNU Mcron 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 General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Mcron. If not, see <http://www.gnu.org/licenses/>.
(define-module (mcron base)
#:use-module (ice-9 match)
#:use-module (mcron environment)
#:use-module (srfi srfi-9)
#:export (add-job
remove-user-jobs
get-schedule
run-job-loop
;; These three are deprecated and not documented.
use-system-job-list
use-user-job-list
clear-system-jobs)
#:re-export (clear-environment-mods
append-environment-mods))
(use-modules (srfi srfi-1) ;; For remove.
(srfi srfi-2)) ;; For and-let*.
;; The list of all jobs known to the system. Each element of the list is
;;
;; (make-job user next-time-function action environment displayable next-time)
;;
;; where action must be a procedure, and the environment is an alist of
;; modifications that need making to the UNIX environment before the action is
;; run. The next-time element is the only one that is modified during the
;; running of a cron process (i.e. all the others are set once and for all at
;; configuration time).
;;
;; The reason we maintain two lists is that jobs in /etc/crontab may be placed
;; in one, and all other jobs go in the other. This makes it possible to remove
;; all the jobs in the first list in one go, and separately we can remove all
;; jobs from the second list which belong to a particular user. This behaviour
;; is required for full vixie compatibility.
(define system-job-list '())
(define user-job-list '())
(define configuration-source 'user)
(define (use-system-job-list) (set! configuration-source 'system))
(define (use-user-job-list) (set! configuration-source 'user))
;; A cron job.
(define-record-type <job>
(make-job user time-proc action environment displayable next-time)
job?
(user job:user) ;object : passwd entry
(time-proc job:next-time-function) ;proc : with one 'time' parameter
(action job:action) ;thunk : user's code
(environment job:environment) ;alist : environment variables
(displayable job:displayable) ;string : visible in schedule
(next-time job:next-time ;number : time in UNIX format
job:next-time-set!))
;; Remove jobs from the user-job-list belonging to this user.
(define (remove-user-jobs user)
(if (or (string? user)
(integer? user))
(set! user (getpw user)))
(set! user-job-list
(remove (lambda (job) (eqv? (passwd:uid user)
(passwd:uid (job:user job))))
user-job-list)))
;; Remove all the jobs on the system job list.
(define (clear-system-jobs) (set! system-job-list '()))
;; Add a new job with the given specifications to the head of the appropriate
;; jobs list.
(define (add-job time-proc action displayable configuration-time
configuration-user)
(let ((entry (make-job configuration-user
time-proc
action
(get-current-environment-mods-copy)
displayable
(time-proc configuration-time))))
(if (eq? configuration-source 'user)
(set! user-job-list (cons entry user-job-list))
(set! system-job-list (cons entry system-job-list)))))
;; Procedure to locate the jobs in the global job-list with the lowest
;; (soonest) next-times. These are the jobs for which we must schedule the mcron
;; program (under any personality) to next wake up. The return value is a cons
;; cell consisting of the next time (maintained in the next-time variable) and a
;; list of the job entries that are to run at this time (maintained in the
;; next-jobs-list variable).
;;
;; The procedure works by first obtaining the time of the first job on the list,
;; and setting this job in the next-jobs-list. Then for each other entry on the
;; job-list, either the job runs earlier than any other that have been scanned,
;; in which case the next-time and next-jobs-list are re-initialized to
;; accomodate, or the job runs at the same time as the next job, in which case
;; the next-jobs-list is simply augmented with the new job, or else the job runs
;; later than others noted in which case we ignore it for now and continue to
;; recurse the list.
(define (find-next-jobs)
(let ((job-list (append system-job-list user-job-list)))
(if (null? job-list)
'(#f . '())
(let ((next-time 2000000000)
(next-jobs-list '()))
(for-each
(lambda (job)
(let ((this-time (job:next-time job)))
(cond ((< this-time next-time)
(set! next-time this-time)
(set! next-jobs-list (list job)))
((eqv? this-time next-time)
(set! next-jobs-list (cons job next-jobs-list))))))
job-list)
(cons next-time next-jobs-list)))))
;; Create a string containing a textual list of the next count jobs to run.
;;
;; Enter a loop of displaying the next set of jobs to run, artificially
;; forwarding the time to the next time point (instead of waiting for it to
;; occur as we would do in a normal run of mcron), and recurse around the loop
;; count times.
;;
;; Note that this has the effect of mutating the job timings. Thus the program
;; must exit after calling this function; the internal data state will be left
;; unusable.
(define (get-schedule count)
(with-output-to-string
(lambda ()
(do ((count count (- count 1)))
((eqv? count 0))
(and-let*
((next-jobs (find-next-jobs))
(time (car next-jobs))
(date-string (strftime "%c %z\n" (localtime time))))
(for-each (lambda (job)
(display date-string)
(display (job:displayable job))
(newline)(newline)
(job:next-time-set! job ((job:next-time-function job)
(job:next-time job))))
(cdr next-jobs)))))))
;; For proper housekeeping, it is necessary to keep a record of the number of
;; child processes we fork off to run the jobs.
(define number-children 0)
;; For every job on the list, fork a process to run it (noting the fact by
;; increasing the number-children counter), and in the new process set up the
;; run-time environment exactly as it should be before running the job proper.
;;
;; In the parent, update the job entry by computing the next time the job needs
;; to run.
(define (run-jobs jobs-list)
(for-each
(lambda (job)
(if (eqv? (primitive-fork) 0)
(dynamic-wind
(const #t)
(lambda ()
(setgid (passwd:gid (job:user job)))
(setuid (passwd:uid (job:user job)))
(chdir (passwd:dir (job:user job)))
(modify-environment (job:environment job) (job:user job))
((job:action job)))
(lambda ()
(primitive-exit 0)))
(begin
(set! number-children (+ number-children 1))
(job:next-time-set! job ((job:next-time-function job)
(current-time))))))
jobs-list))
;; Give any zombie children a chance to die, and decrease the number known to
;; exist.
(define (child-cleanup)
(do () ((or (<= number-children 0)
(eqv? (car (waitpid WAIT_ANY WNOHANG)) 0)))
(set! number-children (- number-children 1))))
(define* (run-job-loop #:optional fd-list)
;; Loop over all job specifications, get a list of the next ones to run (may
;; be more than one). Set an alarm and go to sleep. When we wake, run the
;; jobs and reap any children (old jobs) that have completed. Repeat ad
;; infinitum.
;;
;; Note that, if we wake ahead of time, it can only mean that a signal has
;; been sent by a crontab job to tell us to re-read a crontab file. In this
;; case we break out of the loop here, and let the main procedure deal with
;; the situation (it will eventually re-call this function, thus maintaining
;; the loop).
(call-with-current-continuation
(lambda (break)
(let loop ()
(match (find-next-jobs)
((next-time . next-jobs-lst)
(let ((sleep-time (if next-time
(- next-time (current-time))
2000000000)))
(when (and
(> sleep-time 0)
(not (null? (catch 'system-error
(λ ()
(car (select fd-list '() '() sleep-time)))
(λ (key . args)
(let ((err (car (last args))))
(cond ((member err (list EINTR EAGAIN))
(child-cleanup)
'())
(else
(apply throw key args)))))))))
(break))
(run-jobs next-jobs-lst)
(child-cleanup)
(loop))))))))
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