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-rw-r--r--src/basic/async.c107
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;
+}