src/basic/async.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright 2013 Lennart Poettering
   5
   6   systemd is free software; you can redistribute it and/or modify it
   7   under the terms of the GNU Lesser General Public License as published by
   8   the Free Software Foundation; either version 2.1 of the License, or
   9   (at your option) any later version.
  10
  11   systemd is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   Lesser General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  18 ***/
  19
  20 #include <errno.h>
  21 #include <pthread.h>
  22 #include <stddef.h>
  23 #include <unistd.h>
  24
  25 #include "async.h"
  26 #include "fd-util.h"
  27 #include "log.h"
  28 #include "macro.h"
  29 #include "util.h"
  30
  31 int asynchronous_job(void* (*func)(void *p), void *arg) {
  32         pthread_attr_t a;
  33         pthread_t t;
  34         int r;
  35
  36         /* It kinda sucks that we have to resort to threads to
  37          * implement an asynchronous sync(), but well, such is
  38          * life.
  39          *
  40          * Note that issuing this command right before exiting a
  41          * process will cause the process to wait for the sync() to
  42          * complete. This function hence is nicely asynchronous really
  43          * only in long running processes. */
  44
  45         r = pthread_attr_init(&a);
  46         if (r > 0)
  47                 return -r;
  48
  49         r = pthread_attr_setdetachstate(&a, PTHREAD_CREATE_DETACHED);
  50         if (r > 0)
  51                 goto finish;
  52
  53         r = pthread_create(&t, &a, func, arg);
  54
  55 finish:
  56         pthread_attr_destroy(&a);
  57         return -r;
  58 }
  59
  60 static void *sync_thread(void *p) {
  61         sync();
  62         return NULL;
  63 }
  64
  65 int asynchronous_sync(void) {
  66         log_debug("Spawning new thread for sync");
  67
  68         return asynchronous_job(sync_thread, NULL);
  69 }
  70
  71 static void *close_thread(void *p) {
  72         assert_se(close_nointr(PTR_TO_FD(p)) != -EBADF);
  73         return NULL;
  74 }
  75
  76 int asynchronous_close(int fd) {
  77         int r;
  78
  79         /* This is supposed to behave similar to safe_close(), but
  80          * actually invoke close() asynchronously, so that it will
  81          * never block. Ideally the kernel would have an API for this,
  82          * but it doesn't, so we work around it, and hide this as a
  83          * far away as we can. */
  84
  85         if (fd >= 0) {
  86                 PROTECT_ERRNO;
  87
  88                 r = asynchronous_job(close_thread, FD_TO_PTR(fd));
  89                 if (r < 0)
  90                          assert_se(close_nointr(fd) != -EBADF);
  91         }
  92
  93         return -1;
  94 }