--- /dev/null
+/*
+ * Copyright (c) 2013 Nicira, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <config.h>
+
+#include "latch.h"
+#include <errno.h>
+#include <poll.h>
+#include <unistd.h>
+#include "poll-loop.h"
+#include "socket-util.h"
+
+/* Initializes 'latch' as initially unset. */
+void
+latch_init(struct latch *latch)
+{
+ xpipe_nonblocking(latch->fds);
+}
+
+/* Destroys 'latch'. */
+void
+latch_destroy(struct latch *latch)
+{
+ close(latch->fds[0]);
+ close(latch->fds[1]);
+}
+
+/* Resets 'latch' to the unset state. Returns true if 'latch' was previously
+ * set, false otherwise. */
+bool
+latch_poll(struct latch *latch)
+{
+ char buffer[_POSIX_PIPE_BUF];
+
+ return read(latch->fds[0], buffer, sizeof buffer) > 0;
+}
+
+/* Sets 'latch'.
+ *
+ * Calls are not additive: a single latch_poll() clears out any number of
+ * latch_set(). */
+void
+latch_set(struct latch *latch)
+{
+ ignore(write(latch->fds[1], "", 1));
+}
+
+/* Returns true if 'latch' is set, false otherwise. Does not reset 'latch'
+ * to the unset state. */
+bool
+latch_is_set(const struct latch *latch)
+{
+ struct pollfd pfd;
+ int retval;
+
+ pfd.fd = latch->fds[0];
+ pfd.events = POLLIN;
+ do {
+ retval = poll(&pfd, 1, 0);
+ } while (retval < 0 && errno == EINTR);
+
+ return pfd.revents & POLLIN;
+}
+
+/* Causes the next poll_block() to wake up when 'latch' is set.
+ *
+ * ('where' is used in debug logging. Commonly one would use latch_wait() to
+ * automatically provide the caller's source file and line number for
+ * 'where'.) */
+void
+latch_wait_at(const struct latch *latch, const char *where)
+{
+ poll_fd_wait_at(latch->fds[0], 0, POLLIN, where);
+}