src/basic/async.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include <errno.h>
   4 #include <pthread.h>
   5 #include <stddef.h>
   6 #include <unistd.h>
   7
   8 #include "async.h"
   9 #include "errno-util.h"
  10 #include "fd-util.h"
  11 #include "log.h"
  12 #include "macro.h"
  13 #include "process-util.h"
  14 #include "signal-util.h"
  15 #include "util.h"
  16
  17 int asynchronous_job(void* (*func)(void *p), void *arg) {
  18         sigset_t ss, saved_ss;
  19         pthread_attr_t a;
  20         pthread_t t;
  21         int r, k;
  22
  23         /* It kinda sucks that we have to resort to threads to implement an asynchronous close(), but well, such is
  24          * life. */
  25
  26         r = pthread_attr_init(&a);
  27         if (r > 0)
  28                 return -r;
  29
  30         r = pthread_attr_setdetachstate(&a, PTHREAD_CREATE_DETACHED);
  31         if (r > 0) {
  32                 r = -r;
  33                 goto finish;
  34         }
  35
  36         assert_se(sigfillset(&ss) >= 0);
  37
  38         /* Block all signals before forking off the thread, so that the new thread is started with all signals
  39          * blocked. This way the existence of the new thread won't affect signal handling in other threads. */
  40
  41         r = pthread_sigmask(SIG_BLOCK, &ss, &saved_ss);
  42         if (r > 0) {
  43                 r = -r;
  44                 goto finish;
  45         }
  46
  47         r = pthread_create(&t, &a, func, arg);
  48
  49         k = pthread_sigmask(SIG_SETMASK, &saved_ss, NULL);
  50
  51         if (r > 0)
  52                 r = -r;
  53         else if (k > 0)
  54                 r = -k;
  55         else
  56                 r = 0;
  57
  58 finish:
  59         pthread_attr_destroy(&a);
  60         return r;
  61 }
  62
  63 int asynchronous_sync(pid_t *ret_pid) {
  64         int r;
  65
  66         /* This forks off an invocation of fork() as a child process, in order to initiate synchronization to
  67          * disk. Note that we implement this as helper process rather than thread as we don't want the sync() to hang our
  68          * original process ever, and a thread would do that as the process can't exit with threads hanging in blocking
  69          * syscalls. */
  70
  71         r = safe_fork("(sd-sync)", FORK_RESET_SIGNALS|FORK_CLOSE_ALL_FDS, ret_pid);
  72         if (r < 0)
  73                 return r;
  74         if (r == 0) {
  75                 /* Child process */
  76                 (void) sync();
  77                 _exit(EXIT_SUCCESS);
  78         }
  79
  80         return 0;
  81 }
  82
  83 static void *close_thread(void *p) {
  84         (void) pthread_setname_np(pthread_self(), "close");
  85
  86         assert_se(close_nointr(PTR_TO_FD(p)) != -EBADF);
  87         return NULL;
  88 }
  89
  90 int asynchronous_close(int fd) {
  91         int r;
  92
  93         /* This is supposed to behave similar to safe_close(), but
  94          * actually invoke close() asynchronously, so that it will
  95          * never block. Ideally the kernel would have an API for this,
  96          * but it doesn't, so we work around it, and hide this as a
  97          * far away as we can. */
  98
  99         if (fd >= 0) {
 100                 PROTECT_ERRNO;
 101
 102                 r = asynchronous_job(close_thread, FD_TO_PTR(fd));
 103                 if (r < 0)
 104                          assert_se(close_nointr(fd) != -EBADF);
 105         }
 106
 107         return -1;
 108 }