latch: New module for a thread-safe, signal-safe, pollable doorbell.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Ed Maste <emaste@freebsd.org>

1 files changed, 83 insertions, 0 deletions

diff --git a/lib/latch.c b/lib/latch.c
new file mode 100644
index 00000000..9b130062
--- /dev/null
+++ b/lib/latch.c
@@ -0,0 +1,83 @@
+/*
+ * 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. */
+void
+(latch_wait)(const struct latch *latch, const char *where)
+{
+    (poll_fd_wait)(latch->fds[0], POLLIN, where);
+}