1 files changed, 107 insertions, 0 deletions
diff --git a/src/basic/async.c b/src/basic/async.c
new file mode 100644
index 0000000..c45ca01
--- /dev/null
+++ b/src/basic/async.c
@@ -0,0 +1,107 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include <errno.h>
+#include <pthread.h>
+#include <stddef.h>
+#include <unistd.h>
+
+#include "async.h"
+#include "fd-util.h"
+#include "log.h"
+#include "macro.h"
+#include "process-util.h"
+#include "signal-util.h"
+#include "util.h"
+
+int asynchronous_job(void* (*func)(void *p), void *arg) {
+        sigset_t ss, saved_ss;
+        pthread_attr_t a;
+        pthread_t t;
+        int r, k;
+
+        /* It kinda sucks that we have to resort to threads to implement an asynchronous close(), but well, such is
+         * life. */
+
+        r = pthread_attr_init(&a);
+        if (r > 0)
+                return -r;
+
+        r = pthread_attr_setdetachstate(&a, PTHREAD_CREATE_DETACHED);
+        if (r > 0) {
+                r = -r;
+                goto finish;
+        }
+
+        assert_se(sigfillset(&ss) >= 0);
+
+        /* Block all signals before forking off the thread, so that the new thread is started with all signals
+         * blocked. This way the existence of the new thread won't affect signal handling in other threads. */
+
+        r = pthread_sigmask(SIG_BLOCK, &ss, &saved_ss);
+        if (r > 0) {
+                r = -r;
+                goto finish;
+        }
+
+        r = pthread_create(&t, &a, func, arg);
+
+        k = pthread_sigmask(SIG_SETMASK, &saved_ss, NULL);
+
+        if (r > 0)
+                r = -r;
+        else if (k > 0)
+                r = -k;
+        else
+                r = 0;
+
+finish:
+        pthread_attr_destroy(&a);
+        return r;
+}
+
+int asynchronous_sync(pid_t *ret_pid) {
+        int r;
+
+        /* This forks off an invocation of fork() as a child process, in order to initiate synchronization to
+         * disk. Note that we implement this as helper process rather than thread as we don't want the sync() to hang our
+         * original process ever, and a thread would do that as the process can't exit with threads hanging in blocking
+         * syscalls. */
+
+        r = safe_fork("(sd-sync)", FORK_RESET_SIGNALS|FORK_CLOSE_ALL_FDS, ret_pid);
+        if (r < 0)
+                return r;
+        if (r == 0) {
+                /* Child process */
+                (void) sync();
+                _exit(EXIT_SUCCESS);
+        }
+
+        return 0;
+}
+
+static void *close_thread(void *p) {
+        (void) pthread_setname_np(pthread_self(), "close");
+
+        assert_se(close_nointr(PTR_TO_FD(p)) != -EBADF);
+        return NULL;
+}
+
+int asynchronous_close(int fd) {
+        int r;
+
+        /* This is supposed to behave similar to safe_close(), but
+         * actually invoke close() asynchronously, so that it will
+         * never block. Ideally the kernel would have an API for this,
+         * but it doesn't, so we work around it, and hide this as a
+         * far away as we can. */
+
+        if (fd >= 0) {
+                PROTECT_ERRNO;
+
+                r = asynchronous_job(close_thread, FD_TO_PTR(fd));
+                if (r < 0)
+                         assert_se(close_nointr(fd) != -EBADF);
+        }
+
+        return -1;
+}