src/basic/async.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include <errno.h>
   4 #include <pthread.h>
   5 #include <stddef.h>
   6 #include <unistd.h>
   7
   8 #include "async.h"
   9 #include "fd-util.h"
  10 #include "log.h"
  11 #include "macro.h"
  12 #include "process-util.h"
  13 #include "signal-util.h"
  14 #include "util.h"
  15
  16 int asynchronous_job(void* (*func)(void *p), void *arg) {
  17         sigset_t ss, saved_ss;
  18         pthread_attr_t a;
  19         pthread_t t;
  20         int r, k;
  21
  22         /* It kinda sucks that we have to resort to threads to implement an asynchronous close(), but well, such is
  23          * life. */
  24
  25         r = pthread_attr_init(&a);
  26         if (r > 0)
  27                 return -r;
  28
  29         r = pthread_attr_setdetachstate(&a, PTHREAD_CREATE_DETACHED);
  30         if (r > 0) {
  31                 r = -r;
  32                 goto finish;
  33         }
  34
  35         if (sigfillset(&ss) < 0) {
  36                 r = -errno;
  37                 goto finish;
  38         }
  39
  40         /* Block all signals before forking off the thread, so that the new thread is started with all signals
  41          * blocked. This way the existence of the new thread won't affect signal handling in other threads. */
  42
  43         r = pthread_sigmask(SIG_BLOCK, &ss, &saved_ss);
  44         if (r > 0) {
  45                 r = -r;
  46                 goto finish;
  47         }
  48
  49         r = pthread_create(&t, &a, func, arg);
  50
  51         k = pthread_sigmask(SIG_SETMASK, &saved_ss, NULL);
  52
  53         if (r > 0)
  54                 r = -r;
  55         else if (k > 0)
  56                 r = -k;
  57         else
  58                 r = 0;
  59
  60 finish:
  61         pthread_attr_destroy(&a);
  62         return r;
  63 }
  64
  65 int asynchronous_sync(pid_t *ret_pid) {
  66         int r;
  67
  68         /* This forks off an invocation of fork() as a child process, in order to initiate synchronization to
  69          * disk. Note that we implement this as helper process rather than thread as we don't want the sync() to hang our
  70          * original process ever, and a thread would do that as the process can't exit with threads hanging in blocking
  71          * syscalls. */
  72
  73         r = safe_fork("(sd-sync)", FORK_RESET_SIGNALS|FORK_CLOSE_ALL_FDS, ret_pid);
  74         if (r < 0)
  75                 return r;
  76         if (r == 0) {
  77                 /* Child process */
  78                 (void) sync();
  79                 _exit(EXIT_SUCCESS);
  80         }
  81
  82         return 0;
  83 }
  84
  85 static void *close_thread(void *p) {
  86         (void) pthread_setname_np(pthread_self(), "close");
  87
  88         assert_se(close_nointr(PTR_TO_FD(p)) != -EBADF);
  89         return NULL;
  90 }
  91
  92 int asynchronous_close(int fd) {
  93         int r;
  94
  95         /* This is supposed to behave similar to safe_close(), but
  96          * actually invoke close() asynchronously, so that it will
  97          * never block. Ideally the kernel would have an API for this,
  98          * but it doesn't, so we work around it, and hide this as a
  99          * far away as we can. */
 100
 101         if (fd >= 0) {
 102                 PROTECT_ERRNO;
 103
 104                 r = asynchronous_job(close_thread, FD_TO_PTR(fd));
 105                 if (r < 0)
 106                          assert_se(close_nointr(fd) != -EBADF);
 107         }
 108
 109         return -1;
 110 }