+ int wakeup_fd = shm_get_wakeup_fd(handle, &buf->self._ref);
+
+ if (wakeup_fd >= 0) {
+ sigset_t sigpipe_set, pending_set, old_set;
+ int ret, sigpipe_was_pending = 0;
+
+ /*
+ * Wake-up the other end by
+ * writing a null byte in the
+ * pipe (non-blocking).
+ * Important note: Because
+ * writing into the pipe is
+ * non-blocking (and therefore
+ * we allow dropping wakeup
+ * data, as long as there is
+ * wakeup data present in the
+ * pipe buffer to wake up the
+ * consumer), the consumer
+ * should perform the following
+ * sequence for waiting:
+ * 1) empty the pipe (reads).
+ * 2) check if there is data in
+ * the buffer.
+ * 3) wait on the pipe (poll).
+ *
+ * Discard the SIGPIPE from write(), not
+ * disturbing any SIGPIPE that might be
+ * already pending. If a bogus SIGPIPE
+ * is sent to the entire process
+ * concurrently by a malicious user, it
+ * may be simply discarded.
+ */
+ ret = sigemptyset(&pending_set);
+ assert(!ret);
+ /*
+ * sigpending returns the mask
+ * of signals that are _both_
+ * blocked for the thread _and_
+ * pending for either the thread
+ * or the entire process.
+ */
+ ret = sigpending(&pending_set);
+ assert(!ret);
+ sigpipe_was_pending = sigismember(&pending_set, SIGPIPE);
+ /*
+ * If sigpipe was pending, it
+ * means it was already blocked,
+ * so no need to block it.
+ */
+ if (!sigpipe_was_pending) {
+ ret = sigemptyset(&sigpipe_set);
+ assert(!ret);
+ ret = sigaddset(&sigpipe_set, SIGPIPE);
+ assert(!ret);
+ ret = pthread_sigmask(SIG_BLOCK, &sigpipe_set, &old_set);
+ assert(!ret);
+ }
+ do {
+ ret = write(wakeup_fd, "", 1);
+ } while (ret == -1L && errno == EINTR);
+ if (ret == -1L && errno == EPIPE && !sigpipe_was_pending) {
+ struct timespec timeout = { 0, 0 };
+ do {
+ ret = sigtimedwait(&sigpipe_set, NULL,
+ &timeout);
+ } while (ret == -1L && errno == EINTR);
+ }
+ if (!sigpipe_was_pending) {
+ ret = pthread_sigmask(SIG_SETMASK, &old_set, NULL);
+ assert(!ret);
+ }
+ }